Publications

@article{Lydiard2021,

title = {MRI-guided cardiac-induced target motion tracking for atrial fibrillation cardiac radioablation},

author = {Suzanne Lydiard and Beau Pontré and Nicholas Hindley and Boris S Lowe and Giuseppe Sasso and Paul Keall},

doi = {10.1016/j.radonc.2021.09.025},

issn = {0167-8140},

year  = {2021},

date = {2021-11-00},

journal = {Radiotherapy and Oncology},

volume = {164},

pages = {138--145},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Muurholm2021,

title = {Real-time dose-guidance in radiotherapy: Proof of principle},

author = {Casper Gammelmark Muurholm and Thomas Ravkilde and Simon Skouboe and Esben Worm and Rune Hansen and Morten Høyer and Paul J. Keall and Per R. Poulsen},

doi = {10.1016/j.radonc.2021.09.024},

issn = {0167-8140},

year  = {2021},

date = {2021-11-00},

journal = {Radiotherapy and Oncology},

volume = {164},

pages = {175--182},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hindley2021,

title = {Proof-of-concept for x-ray based real-time image guidance during cardiac radioablation},

author = {Nicholas Hindley and Suzanne Lydiard and Chun-Chien Shieh and Paul Keall},

doi = {10.1088/1361-6560/ac1834},

issn = {1361-6560},

year  = {2021},

date = {2021-09-07},

journal = {Phys. Med. Biol.},

volume = {66},

number = {17},

publisher = {IOP Publishing},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mylonas2021,

title = {A review of artificial intelligence applications for motion tracking in radiotherapy},

author = {Adam Mylonas and Jeremy Booth and Doan Trang Nguyen},

doi = {10.1111/1754-9485.13285},

issn = {1754-9485},

year  = {2021},

date = {2021-08-00},

journal = {J Med Imag Rad Onc},

volume = {65},

number = {5},

pages = {596--611},

publisher = {Wiley},

abstract = {AbstractDuring radiotherapy, the organs and tumour move as a result of the dynamic nature of the body; this is known as intrafraction motion. Intrafraction motion can result in tumour underdose and healthy tissue overdose, thereby reducing the effectiveness of the treatment while increasing toxicity to the patients. There is a growing appreciation of intrafraction target motion management by the radiation oncology community. Real‐time image‐guided radiation therapy (IGRT) can track the target and account for the motion, improving the radiation dose to the tumour and reducing the dose to healthy tissue. Recently, artificial intelligence (AI)‐based approaches have been applied to motion management and have shown great potential. In this review, four main categories of motion management using AI are summarised: marker‐based tracking, markerless tracking, full anatomy monitoring and motion prediction. Marker‐based and markerless tracking approaches focus on tracking the individual target throughout the treatment. Full anatomy algorithms monitor for intrafraction changes in the full anatomy within the field of view. Motion prediction algorithms can be used to account for the latencies due to the time for the system to localise, process and act.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{O'Brien2021,

title = {The first-in-human implementation of adaptive 4D cone beam CT for lung cancer radiotherapy: 4DCBCT in less time with less dose},

author = {Ricky T. O'Brien and Owen Dillon and Benjamin Lau and Armia George and Sandie Smith and Andrew Wallis and Jan-Jakob Sonke and Paul J. Keall and Shalini K. Vinod},

doi = {10.1016/j.radonc.2021.05.021},

issn = {0167-8140},

year  = {2021},

date = {2021-08-00},

journal = {Radiotherapy and Oncology},

volume = {161},

pages = {29--34},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hewson2021,

title = {First experimental evaluation of multi-target multileaf collimator tracking during volumetric modulated arc therapy for locally advanced prostate cancer},

author = {Emily A. Hewson and Andrew Dipuglia and John Kipritidis and Yuanyuan Ge and Ricky O'Brien and Stephanie Roderick and Linda Bell and Per R. Poulsen and Thomas Eade and Jeremy T. Booth and Paul J. Keall and Doan T. Nguyen},

doi = {10.1016/j.radonc.2021.05.001},

issn = {0167-8140},

year  = {2021},

date = {2021-07-00},

journal = {Radiotherapy and Oncology},

volume = {160},

pages = {212--220},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hardcastle2021,

title = {Quantification of the geometric uncertainty when using implanted markers as a surrogate for lung tumor motion},

author = {Nicholas Hardcastle and Adam Briggs and Vincent Caillet and Giorgios Angelis and Danielle Chrystall and Dasantha Jayamanne and Meegan Shepherd and Ben Harris and Carol Haddad and Thomas Eade and Paul Keall and Jeremy Booth},

doi = {10.1002/mp.14788},

issn = {2473-4209},

year  = {2021},

date = {2021-06-00},

journal = {Medical Physics},

volume = {48},

number = {6},

pages = {2724--2732},

publisher = {Wiley},

abstract = {BackgroundFiducial markers are used as surrogates for tumor location during radiation therapy treatment. Developments in lung fiducial marker and implantation technology have provided a means to insert markers endobronchially for tracking of lung tumors. This study quantifies the surrogacy uncertainty (SU) when using endobronchially implanted markers as a surrogate for lung tumor position.MethodsWe evaluated SU for 17 patients treated in a prospective electromagnetic‐guided MLC tracking trial. Tumor and markers were segmented on all phases of treatment planning 4DCTs and all frames of pretreatment kilovoltage fluoroscopy acquired from lateral and frontal views. The difference in tumor and marker position relative to end‐exhale position was calculated as the SU for both imaging methods and the distributions of uncertainties analyzed.ResultsThe mean (range) tumor motion amplitude in the 4DCT scan was 5.9 mm (1.7–11.7 mm) in the superior–inferior (SI) direction, 2.2 mm (0.9–5.5 mm) in the left–right (LR) direction, and 3.9 mm (1.2–12.9 mm) in the anterior–posterior (AP) direction. Population‐based analysis indicated symmetric SU centered close to 0 mm, with maximum 5th/95th percentile values over all axes of −2.0 mm/2.1 mm with 4DCT, and −2.3/1.3 mm for fluoroscopy. There was poor correlation between the SU measured with 4DCT and that measured with fluoroscopy on a per‐patient basis. We observed increasing SU with increasing surrogate motion. Based on fluoroscopy analysis, the mean (95% CI) SU was 5% (2%–8%) of the motion magnitude in the SI direction, 16% (6%–26%) of the motion magnitude in the LR direction, and 33% (23%–42%) of the motion magnitude in the AP direction. There was no dependence of SU on marker distance from the tumor.ConclusionWe have quantified SU due to use of implanted markers as surrogates for lung tumor motion. Population 95th percentile range are up to 2.3 mm, indicating the approximate contribution of SU to total geometric uncertainty. SU was relatively small compared with the SI motion, but substantial compared with LR and AP motion. Due to uncertainty in estimations of patient‐specific SU, it is recommended that population‐based margins are used to account for this component of the total geometric uncertainty.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Gardner2021,

title = {The adaptation and investigation of cone-beam CT reconstruction algorithms for horizontal rotation fixed-gantry scans of rabbits},

author = {Mark Gardner and Owen Dillon and Chun-Chien Shieh and Ricky O’Brien and Emily Debrot and Jeffrey Barber and Verity Ahern and Peter Bennett and Soo-Min Heng and Stéphanie Corde and Michael Jackson and Paul Keall},

doi = {10.1088/1361-6560/abf9dd},

issn = {1361-6560},

year  = {2021},

date = {2021-05-21},

journal = {Phys. Med. Biol.},

volume = {66},

number = {10},

publisher = {IOP Publishing},

abstract = {Abstract

               Fixed-gantry radiation therapy has been proposed as a low-cost alternative to the conventional rotating-gantry radiation therapy, that may help meet the rising global treatment demand. Fixed-gantry systems require gravitational motion compensated reconstruction algorithms to produce cone-beam CT (CBCT) images of sufficient quality for image guidance. The aim of this work was to adapt and investigate five CBCT reconstruction algorithms for fixed-gantry CBCT images. The five algorithms investigated were Feldkamp–Davis–Kress (FDK), prior image constrained compressed sensing (PICCS), gravitational motion compensated FDK (GMCFDK), motion compensated PICCS (MCPICCS) (a novel CBCT reconstruction algorithm) and simultaneous motion estimation and iterative reconstruction (SMEIR). Fixed-gantry and rotating-gantry CBCT scans were acquired of 3 rabbits, with the rotating-gantry scans used as a reference. Projections were sorted into rotation bins, based on the angle of rotation of the rabbit during image acquisition. The algorithms were compared using the structural similarity index measure root mean square error, and reconstruction time. Evaluation of the reconstructed volumes showed that, when compared with the reference rotating-gantry volume, the conventional FDK algorithm did not accurately reconstruct fixed-gantry CBCT scans. Whilst the PICCS reconstruction algorithm reduced some motion artefacts, the motion estimation reconstruction methods (GMCFDK, MCPICCS and SMEIR) were able to greatly reduce the effect of motion artefacts on the reconstructed volumes. This finding was verified quantitatively, with GMCFDK, MCPICCS and SMEIR reconstructions having RMSE 17%–19% lower and SSIM 1% higher than a conventional FDK. However, all motion compensated fixed-gantry CBCT reconstructions had a 56%–61% higher RMSE and 1.5% lower SSIM than FDK reconstructions of conventional rotating-gantry CBCT scans. The results show that motion compensation is required to reduce motion artefacts for fixed-gantry CBCT reconstructions. This paper further demonstrates the feasibility of fixed-gantry CBCT scans, and the ability of CBCT reconstruction algorithms to compensate for motion due to horizontal rotation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Keall2021,

title = {AAPM Task Group 264: The safe clinical implementation of MLC tracking in radiotherapy},

author = {Paul J. Keall and Amit Sawant and Ross I. Berbeco and Jeremy T. Booth and Byungchul Cho and Laura I. Cerviño and Eileen Cirino and Sonja Dieterich and Martin F. Fast and Peter B. Greer and Per Munck af Rosenschöld and Parag J. Parikh and Per Rugaard Poulsen and Lakshmi Santanam and George W. Sherouse and Jie Shi and Sotirios Stathakis},

doi = {10.1002/mp.14625},

issn = {2473-4209},

year  = {2021},

date = {2021-05-00},

journal = {Medical Physics},

volume = {48},

number = {5},

publisher = {Wiley},

abstract = {The era of real‐time radiotherapy is upon us. Robotic and gimbaled linac tracking are clinically established technologies with the clinical realization of couch tracking in development. Multileaf collimators (MLCs) are a standard equipment for most cancer radiotherapy systems, and therefore MLC tracking is a potentially widely available technology. MLC tracking has been the subject of theoretical and experimental research for decades and was first implemented for patient treatments in 2013. The AAPM Task Group 264 Safe Clinical Implementation of MLC Tracking in Radiotherapy Report was charged to proactively provide the broader radiation oncology community with (a) clinical implementation guidelines including hardware, software, and clinical indications for use, (b) commissioning and quality assurance recommendations based on early user experience, as well as guidelines on Failure Mode and Effects Analysis, and (c) a discussion of potential future developments. The deliverables from this report include: an explanation of MLC tracking and its historical development; terms and definitions relevant to MLC tracking; the clinical benefit of, clinical experience with and clinical implementation guidelines for MLC tracking; quality assurance guidelines, including example quality assurance worksheets; a clinical decision pathway, future outlook and overall recommendations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Reynolds2021,

title = {Adaptive CaRdiac cOne BEAm computed Tomography (ACROBEAT): Developing the next generation of cardiac cone beam CT imaging},

author = {Tess Reynolds and Owen Dillon and Joseph Prinable and Brendan Whelan and Paul J. Keall and Ricky T. O’Brien},

doi = {10.1002/mp.14811},

issn = {2473-4209},

year  = {2021},

date = {2021-05-00},

journal = {Medical Physics},

volume = {48},

number = {5},

pages = {2543--2552},

publisher = {Wiley},

abstract = {PurposeAn important factor when considering the use of interventional cone beam computed tomography (CBCT) imaging during cardiac procedures is the trade‐off between imaging dose and image quality. Accordingly, Adaptive CaRdiac cOne BEAm computed Tomography (ACROBEAT) presents an alternative acquisition method, adapting the gantry velocity and projection rate of CBCT imaging systems in accordance with a patient’s electrocardiogram (ECG) signal in real‐time. The aim of this study was to experimentally investigate that ACROBEAT acquisitions deliver improved image quality compared to conventional cardiac CBCT imaging protocols with fewer projections acquired.MethodsThe Siemens ARTIS pheno (Siemens Healthcare, GmbH, Germany), a robotic CBCT C‐arm system, was used to compare ACROBEAT with a commercially available conventional cardiac imaging protocol that utilizes multisweep retrospective ECG‐gated acquisition. For ACROBEAT, real‐time control of the gantry position was enabled through the Siemens Test Automation Control system. ACROBEAT and conventional image acquisitions of the CIRS Dynamic Cardiac Phantom were performed, using five patient‐measured ECG traces. The traces had average heart rates of 56, 64, 76, 86, and 100 bpm. The total number of acquired projections was compared between the ACROBEAT and conventional acquisition methods. The image quality was assessed via the contrast‐to‐noise ratio (CNR), structural similarity index (SSIM), and root‐mean square error (RMSE).ResultsCompared to the conventional protocol, ACROBEAT reduced the total number of projections acquired by 90%. The visual image quality provided by the ACROBEAT acquisitions, across all traces, matched or improved compared to conventional acquisition and was independent of the patient’s heart rate. Across all traces, ACROBEAT averaged 1.4 times increase in the CNR, a 23% increase in the SSIM and a 29% decrease in the RMSE compared to conventional and was independent of the patient’s heart rate.ConclusionAdaptive patient imaging is feasible on a clinical robotic CBCT system, delivering higher quality images while reducing the number of projections acquired by 90% compared to conventional cardiac imaging protocols.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Keall2021b,

title = {AAPM Task Group 264: The safe clinical implementation of MLC tracking in radiotherapy},

author = {Paul J. Keall and Amit Sawant and Ross I. Berbeco and Jeremy T. Booth and Byungchul Cho and Laura I. Cerviño and Eileen Cirino and Sonja Dieterich and Martin F. Fast and Peter B. Greer and Per Munck af Rosenschöld and Parag J. Parikh and Per Rugaard Poulsen and Lakshmi Santanam and George W. Sherouse and Jie Shi and Sotirios Stathakis},

doi = {10.1002/mp.14625},

issn = {2473-4209},

year  = {2021},

date = {2021-05-00},

journal = {Medical Physics},

volume = {48},

number = {5},

publisher = {Wiley},

abstract = {The era of real‐time radiotherapy is upon us. Robotic and gimbaled linac tracking are clinically established technologies with the clinical realization of couch tracking in development. Multileaf collimators (MLCs) are a standard equipment for most cancer radiotherapy systems, and therefore MLC tracking is a potentially widely available technology. MLC tracking has been the subject of theoretical and experimental research for decades and was first implemented for patient treatments in 2013. The AAPM Task Group 264 Safe Clinical Implementation of MLC Tracking in Radiotherapy Report was charged to proactively provide the broader radiation oncology community with (a) clinical implementation guidelines including hardware, software, and clinical indications for use, (b) commissioning and quality assurance recommendations based on early user experience, as well as guidelines on Failure Mode and Effects Analysis, and (c) a discussion of potential future developments. The deliverables from this report include: an explanation of MLC tracking and its historical development; terms and definitions relevant to MLC tracking; the clinical benefit of, clinical experience with and clinical implementation guidelines for MLC tracking; quality assurance guidelines, including example quality assurance worksheets; a clinical decision pathway, future outlook and overall recommendations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lau2021,

title = {Reducing 4DCBCT scan time and dose through motion compensated acquisition and reconstruction},

author = {Benjamin K F Lau and Tess Reynolds and Andrew Wallis and Sandie Smith and Armia George and Paul J Keall and Jan-Jakob Sonke and Shalini K Vinod and Owen Dillon and Ricky T O’Brien},

doi = {10.1088/1361-6560/abebfb},

issn = {1361-6560},

year  = {2021},

date = {2021-04-07},

journal = {Phys. Med. Biol.},

volume = {66},

number = {7},

publisher = {IOP Publishing},

abstract = {Abstract

               Conventional 4DCBCT captures 1320 projections across 4 min. Adaptive 4DCBCT has been developed to reduce imaging dose and scan time. This study investigated reconstruction algorithms that best complement adaptive 4DCBCT acquisition for reducing imaging dose and scan time whilst maintaining or improving image quality compared to conventional 4DCBCT acquisition using real patient data from the first 10 adaptive 4DCBCT patients. Adaptive 4DCBCT was implemented in the ADaptive CT Acquisition for Personalized Thoracic imaging clinical trial. Adaptive 4DCBCT modulates gantry rotation speed and kV acquisition rate in response to the patient’s real-time respiratory signal, ensuring even angular spacing between projections at each respiratory phase. We examined the first 10 lung cancer radiotherapy patients that received adaptive 4DCBCT. Fast, 200-projection scans over 60–80 s, and slower, 600-projection scans over ∼240 s, were obtained after routine patient treatment and compared against conventional 4DCBCT acquisition. Adaptive 4DCBCT acquisitions were reconstructed using Feldkamp−Davis−Kress (FDK), McKinnon–Bates (MKB), Motion Compensated FDK (MCFDK) and Motion Compensated MKB (MCMKB) algorithms. Reconstructions were assessed via, Structural SIMilarity (SSIM), Signal-to-Noise-Ratio (SNR), Contrast-to-Noise-Ratio (CNR), Tissue Interface Sharpness of Diaphragm (TIS-D) and Tumor (TIS-T). The 200- and 600-projection adaptive 4DCBCT acquisition corresponded to 85% and 55% reduction in imaging dose, shorter and similar scan times of approximately 90 s and 236 s respectively, compared to conventional 4DCBCT acquisition. 200- and 600-projection adaptive 4DCBCT reconstructions achieved more than 0.900 SSIM relative to conventional 4DCBCT acquisition. Compared to conventional 4DCBCT acquisition, 200-projection adaptive 4DCBCT reconstructions achieved higher SNR, CNR, TIS-T, TIS-D with motion compensated algorithms, MCFDK (208%, 159%, 174%, 247%) and MCMKB (214%, 173%, 266%, 245%) respectively. The 200-projection adaptive 4DCBCT MCFDK- and MCMKB-reconstruction results show image quality improvements are possible even with 85% fewer projections acquired. We established acquisition-reconstruction protocols that provide substantial reductions in imaging time and dose whilst improving image quality.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Liu2021,

title = {Pre-treatment and real-time image guidance for a fixed-beam radiotherapy system},

author = {Paul Z Y Liu and Mark Gardner and Soo Min Heng and Chun-Chen Shieh and Doan Trang Nguyen and Emily Debrot and Ricky O’Brien and Simon Downes and Michael Jackson and Paul J Keall},

doi = {10.1088/1361-6560/abdc12},

issn = {1361-6560},

year  = {2021},

date = {2021-03-21},

journal = {Phys. Med. Biol.},

volume = {66},

number = {6},

publisher = {IOP Publishing},

abstract = {Abstract

               

                  Purpose. A radiotherapy system with a fixed treatment beam and a rotating patient positioning system could be smaller, more robust and more cost effective compared to conventional rotating gantry systems. However, patient rotation could cause anatomical deformation and compromise treatment delivery. In this work, we demonstrate an image-guided treatment workflow with a fixed beam prototype system that accounts for deformation during rotation to maintain dosimetric accuracy. Methods. The prototype system consists of an Elekta Synergy linac with the therapy beam orientated downward and a custom-built patient rotation system (PRS). A phantom that deforms with rotation was constructed and rotated within the PRS to quantify the performance of two image guidance techniques: motion compensated cone-beam CT (CBCT) for pre-treatment volumetric imaging and kilovoltage infraction monitoring (KIM) for real-time image guidance. The phantom was irradiated with a 3D conformal beam to evaluate the dosimetric accuracy of the workflow. Results. The motion compensated CBCT was used to verify pre-treatment position and the average calculated position was within −0.3 ± 1.1 mm of the phantom’s ground truth position at 0°. KIM tracked the position of the target in real-time as the phantom was rotated and the average calculated position was within −0.2 ± 0.8 mm of the phantom’s ground truth position. A 3D conformal treatment delivered on the prototype system with image guidance had a 3%/2 mm gamma pass rate of 96.3% compared to 98.6% delivered using a conventional rotating gantry linac. Conclusions. In this work, we have shown that image guidance can be used with fixed-beam treatment systems to measure and account for changes in target position in order to maintain dosimetric coverage during horizontal rotation. This treatment modality could provide a viable treatment option when there insufficient space for a conventional linear accelerator or where the cost is prohibitive.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mejnertsen2021,

title = {Dose-based optimisation for multi-leaf collimator tracking during radiation therapy},

author = {Lars Mejnertsen and Emily Hewson and Doan Trang Nguyen and Jeremy Booth and Paul Keall},

doi = {10.1088/1361-6560/abe836},

issn = {1361-6560},

year  = {2021},

date = {2021-03-21},

journal = {Phys. Med. Biol.},

volume = {66},

number = {6},

publisher = {IOP Publishing},

abstract = {Abstract

               Motion in the patient anatomy causes a reduction in dose delivered to the target, while increasing dose to healthy tissue. Multi-leaf collimator (MLC) tracking has been clinically implemented to adapt dose delivery to account for intrafraction motion. Current methods shift the planned MLC aperture in the direction of motion, then optimise the new aperture based on the difference in fluence. The drawback of these methods is that 3D dose, a function of patient anatomy and MLC aperture sequence, is not properly accounted for. To overcome the drawback of current fluence-based methods, we have developed and investigated real-time adaptive MLC tracking based on dose optimisation. A novel MLC tracking algorithm, dose optimisation, has been developed which accounts for the moving patient anatomy by optimising the MLC based on the dose delivered during treatment, simulated using a simplified dose calculation algorithm. The MLC tracking with dose optimisation method was applied in silico to a prostate cancer VMAT treatment dataset with observed intrafraction motion. Its performance was compared to MLC tracking with fluence optimisation and, as a baseline, without MLC tracking. To quantitatively assess performance, we computed the dose error and 3D γ failure rate (2 mm/2%) for each fraction and method. Dose optimisation achieved a γ failure rate of (4.7 ± 1.2)% (mean and standard deviation) over all fractions, which was significantly lower than fluence optimisation (7.5 ± 2.9)% (Wilcoxon sign-rank test p < 0.01). Without MLC tracking, a γ failure rate of (15.3 ± 12.9)% was achieved. By considering the accumulation of dose in the moving anatomy during treatment, dose optimisation is able to optimise the aperture to actively target regions of underdose while avoiding overdose.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Reynolds2021b,

title = {Minimizing 4DCBCT imaging dose and scan time with Respiratory Motion Guided 4DCBCT: a pre-clinical investigation},

author = {Tess Reynolds and Praise Lim and Paul J Keall and Ricky O’Brien},

doi = {10.1088/2057-1976/abdc82},

issn = {2057-1976},

year  = {2021},

date = {2021-03-01},

journal = {Biomed. Phys. Eng. Express},

volume = {7},

number = {2},

publisher = {IOP Publishing},

abstract = {Abstract

               Current conventional 4D Cone Beam Computed Tomography (4DCBCT) imaging is hampered by inconsistent patient breathing that leads to long scan times, reduced image quality and high imaging dose. To address these limitations, Respiratory Motion Guided 4D cone beam computed tomography (RMG-4DCBCT) uses mathematical optimization to adapt the gantry rotation speed and projection acquisition rate in real-time in response to changes in the patient’s breathing rate. Here, RMG-4DCBCT is implemented on an Elekta Synergy linear accelerator to determine the minimum achievable imaging dose. 8 patient-measured breathing traces were programmed into a 1D motion stage supporting a 3D-printed anthropomorphic thorax phantom. The respiratory phase and current gantry position were calculated in real-time with the RMG-4DCBCT software, which in turn modulated the gantry rotation speed and suppressed projection acquisition. Specifically, the effect of acquiring 20, 25, 30, 35 and 40 projections/respiratory phase bin RMG scans on scan time and image quality was assessed. Reconstructed image quality was assessed via the contrast-to-noise ratio (CNR) and the Edge Response Width (ERW) metrics. The performance of the system in terms of gantry control accuracy was also assessed via an analysis of the angular separation between adjacent projections. The median CNR increased linearly from 5.90 (20 projections/bin) to 8.39 (40 projections/bin). The ERW did not significantly change from 1.08 mm (20 projections/bin) to 1.07 mm (40 projections/bin), indicating the sharpness is not dependent on the total number of projections acquired. Scan times increased with increasing total projections and slower breathing rates. Across all 40 RMG-4DCBCT scans performed, the average difference in the acquired and desired angular separation between projections was 0.64°. RMG-4DCBCT provides the opportunity to enable fast low-dose 4DCBCT (∼70 s, 200 projections), without compromising on current clinical image quality.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lydiard,PGDip2021,

title = {A Review of Cardiac Radioablation (CR) for Arrhythmias: Procedures, Technology, and Future Opportunities},

author = {Suzanne Lydiard, PGDip and Oliver Blanck and Geoffrey Hugo and Ricky O’Brien and Paul Keall},

doi = {10.1016/j.ijrobp.2020.10.036},

issn = {0360-3016},

year  = {2021},

date = {2021-03-00},

journal = {International Journal of Radiation Oncology*Biology*Physics},

volume = {109},

number = {3},

pages = {783--800},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lydiard2021b,

title = {Cardiac radioablation for atrial fibrillation: Target motion characterization and treatment delivery considerations},

author = {Suzanne Lydiard and Beau Pontré and Boris S. Lowe and Helen Ball and Giuseppe Sasso and Paul Keall},

doi = {10.1002/mp.14661},

issn = {2473-4209},

year  = {2021},

date = {2021-03-00},

journal = {Medical Physics},

volume = {48},

number = {3},

pages = {931--941},

publisher = {Wiley},

abstract = {PurposeThe safe delivery of cardiac radioablation (CR) for atrial fibrillation (AF) is challenged by multi‐direction target motion, cardiac rate variability, target proximity to critical structures, and the importance of complete target dose coverage for therapeutic benefit. Careful selection of appropriate treatment procedures is therefore essential. This work characterizes AF cardiac radioablation target motion and target proximity to surrounding structures in both healthy and AF participants to guide optimal treatment technique and technology choice.MethodsTen healthy participants and five participants with AF underwent MRI acquisition. Multi‐slice, cardiac‐gated, breath‐hold cines were acquired and interpolated to create three‐dimensional images for 18–30 cardiac phases. Treatment targets at the left and right pulmonary vein ostia (CTVLeft and CTVRight respectively) and adjacent cardiac structures were contoured and their displacements throughout the cardiac cycle were assessed. Target proximity to surrounding structures were measured. Free‐breathing real‐time two‐dimensional cine images were also acquired at 4 Hz frequency for between 1‐ and 2‐min duration. The motion of easily identifiable points within the target, diaphragm and sternum was measured to assess respiratory motion.ResultsTarget motion due to cardiac contraction was most prominent in the medial‐lateral direction and of 4–5 mm magnitude. CTVRight displacements were smaller in participants with AF than healthy participants in normal sinus rhythm. Nearby cardiac structures often moved with different magnitudes and motion trajectories. CTVLeft and/or CTVRight were in direct contact with the esophagus in 73% of participants. Target motion due to respiration was most prominent in the superior–inferior direction and of 13–14 mm magnitude in both healthy and AF participants.ConclusionAF CR target motion and relative displacement was characterized. The combination of target motion magnitude and relative displacement to critical structures highlights the importance of personalizing motion compensation techniques for effective AF CR treatments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zwan2021,

title = {Toward real‐time verification for MLC tracking treatments using time‐resolved EPID imaging},

author = {Benjamin J. Zwan and Vincent Caillet and Jeremy T. Booth and Emma Colvill and Todsaporn Fuangrod and Ricky O'Brien and Adam Briggs and Daryl J. O’Connor and Paul J. Keall and Peter B. Greer},

doi = {10.1002/mp.14675},

issn = {2473-4209},

year  = {2021},

date = {2021-03-00},

journal = {Medical Physics},

volume = {48},

number = {3},

pages = {953--964},

publisher = {Wiley},

abstract = {PurposeIn multileaf collimator (MLC) tracking, the MLC positions from the original treatment plan are continuously modified to account for intrafraction tumor motion. As the treatment is adapted in real time, there is additional risk of delivery errors which cannot be detected using traditional pretreatment dose verification. The purpose of this work is to develop a system for real‐time geometric verification of MLC tracking treatments using an electronic portal imaging device (EPID).MethodsMLC tracking was utilized during volumetric modulated arc therapy (VMAT). During these deliveries, treatment beam images were taken at 9.57 frames per second using an EPID and frame grabber computer. MLC positions were extracted from each image frame and used to assess delivery accuracy using three geometric measures: the location, size, and shape of the radiation field. The EPID‐measured field location was compared to the tumor motion measured by implanted electromagnetic markers. The size and shape of the beam were compared to the size and shape from the original treatment plan, respectively. This technique was validated by simulating errors in phantom test deliveries and by comparison between EPID measurements and treatment log files. The method was applied offline to images acquired during the LIGHT Stereotactic Ablative Body Radiotherapy (SABR) clinical trial, where MLC tracking was performed for 17 lung cancer patients. The EPID‐based verification results were subsequently compared to post‐treatment dose reconstruction.ResultsSimulated field location errors were detected during phantom validation tests with an uncertainty of 0.28 mm (parallel to MLC motion) and 0.38 mm (perpendicular), expressed as a root‐mean‐square error (RMSError). For simulated field size errors, the RMSError was 0.47 cm2 and field shape changes were detected for random errors with standard deviation ≥ 2.5 mm. For clinical lung SABR deliveries, field location errors of 1.6 mm (parallel MLC motion) and 4.9 mm (perpendicular) were measured (expressed as a full‐width‐half‐maximum). The mean and standard deviation of the errors in field size and shape were 0.0 ± 0.3 cm2 and 0.3 ± 0.1 (expressed as a translation‐invariant normalized RMS). No correlation was observed between geometric errors during each treatment fraction and dosimetric errors in the reconstructed dose to the target volume for this cohort of patients.ConclusionA system for real‐time delivery verification has been developed for MLC tracking using time‐resolved EPID imaging. The technique has been tested offline in phantom‐based deliveries and clinical patient deliveries and was used to independently verify the geometric accuracy of the MLC during MLC tracking radiotherapy.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lydiard2021c,

title = {Cardiac radioablation for atrial fibrillation: Target motion characterization and treatment delivery considerations},

author = {Suzanne Lydiard and Beau Pontré and Boris S. Lowe and Helen Ball and Giuseppe Sasso and Paul Keall},

doi = {10.1002/mp.14661},

issn = {2473-4209},

year  = {2021},

date = {2021-03-00},

journal = {Medical Physics},

volume = {48},

number = {3},

pages = {931--941},

publisher = {Wiley},

abstract = {PurposeThe safe delivery of cardiac radioablation (CR) for atrial fibrillation (AF) is challenged by multi‐direction target motion, cardiac rate variability, target proximity to critical structures, and the importance of complete target dose coverage for therapeutic benefit. Careful selection of appropriate treatment procedures is therefore essential. This work characterizes AF cardiac radioablation target motion and target proximity to surrounding structures in both healthy and AF participants to guide optimal treatment technique and technology choice.MethodsTen healthy participants and five participants with AF underwent MRI acquisition. Multi‐slice, cardiac‐gated, breath‐hold cines were acquired and interpolated to create three‐dimensional images for 18–30 cardiac phases. Treatment targets at the left and right pulmonary vein ostia (CTVLeft and CTVRight respectively) and adjacent cardiac structures were contoured and their displacements throughout the cardiac cycle were assessed. Target proximity to surrounding structures were measured. Free‐breathing real‐time two‐dimensional cine images were also acquired at 4 Hz frequency for between 1‐ and 2‐min duration. The motion of easily identifiable points within the target, diaphragm and sternum was measured to assess respiratory motion.ResultsTarget motion due to cardiac contraction was most prominent in the medial‐lateral direction and of 4–5 mm magnitude. CTVRight displacements were smaller in participants with AF than healthy participants in normal sinus rhythm. Nearby cardiac structures often moved with different magnitudes and motion trajectories. CTVLeft and/or CTVRight were in direct contact with the esophagus in 73% of participants. Target motion due to respiration was most prominent in the superior–inferior direction and of 13–14 mm magnitude in both healthy and AF participants.ConclusionAF CR target motion and relative displacement was characterized. The combination of target motion magnitude and relative displacement to critical structures highlights the importance of personalizing motion compensation techniques for effective AF CR treatments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lydiard2021d,

title = {Cardiac radioablation for atrial fibrillation: Target motion characterization and treatment delivery considerations},

author = {Suzanne Lydiard and Beau Pontré and Boris S. Lowe and Helen Ball and Giuseppe Sasso and Paul Keall},

doi = {10.1002/mp.14661},

issn = {2473-4209},

year  = {2021},

date = {2021-03-00},

journal = {Medical Physics},

volume = {48},

number = {3},

pages = {931--941},

publisher = {Wiley},

abstract = {PurposeThe safe delivery of cardiac radioablation (CR) for atrial fibrillation (AF) is challenged by multi‐direction target motion, cardiac rate variability, target proximity to critical structures, and the importance of complete target dose coverage for therapeutic benefit. Careful selection of appropriate treatment procedures is therefore essential. This work characterizes AF cardiac radioablation target motion and target proximity to surrounding structures in both healthy and AF participants to guide optimal treatment technique and technology choice.MethodsTen healthy participants and five participants with AF underwent MRI acquisition. Multi‐slice, cardiac‐gated, breath‐hold cines were acquired and interpolated to create three‐dimensional images for 18–30 cardiac phases. Treatment targets at the left and right pulmonary vein ostia (CTVLeft and CTVRight respectively) and adjacent cardiac structures were contoured and their displacements throughout the cardiac cycle were assessed. Target proximity to surrounding structures were measured. Free‐breathing real‐time two‐dimensional cine images were also acquired at 4 Hz frequency for between 1‐ and 2‐min duration. The motion of easily identifiable points within the target, diaphragm and sternum was measured to assess respiratory motion.ResultsTarget motion due to cardiac contraction was most prominent in the medial‐lateral direction and of 4–5 mm magnitude. CTVRight displacements were smaller in participants with AF than healthy participants in normal sinus rhythm. Nearby cardiac structures often moved with different magnitudes and motion trajectories. CTVLeft and/or CTVRight were in direct contact with the esophagus in 73% of participants. Target motion due to respiration was most prominent in the superior–inferior direction and of 13–14 mm magnitude in both healthy and AF participants.ConclusionAF CR target motion and relative displacement was characterized. The combination of target motion magnitude and relative displacement to critical structures highlights the importance of personalizing motion compensation techniques for effective AF CR treatments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zwan2021b,

title = {Toward real‐time verification for MLC tracking treatments using time‐resolved EPID imaging},

author = {Benjamin J. Zwan and Vincent Caillet and Jeremy T. Booth and Emma Colvill and Todsaporn Fuangrod and Ricky O'Brien and Adam Briggs and Daryl J. O’Connor and Paul J. Keall and Peter B. Greer},

doi = {10.1002/mp.14675},

issn = {2473-4209},

year  = {2021},

date = {2021-03-00},

journal = {Medical Physics},

volume = {48},

number = {3},

pages = {953--964},

publisher = {Wiley},

abstract = {PurposeIn multileaf collimator (MLC) tracking, the MLC positions from the original treatment plan are continuously modified to account for intrafraction tumor motion. As the treatment is adapted in real time, there is additional risk of delivery errors which cannot be detected using traditional pretreatment dose verification. The purpose of this work is to develop a system for real‐time geometric verification of MLC tracking treatments using an electronic portal imaging device (EPID).MethodsMLC tracking was utilized during volumetric modulated arc therapy (VMAT). During these deliveries, treatment beam images were taken at 9.57 frames per second using an EPID and frame grabber computer. MLC positions were extracted from each image frame and used to assess delivery accuracy using three geometric measures: the location, size, and shape of the radiation field. The EPID‐measured field location was compared to the tumor motion measured by implanted electromagnetic markers. The size and shape of the beam were compared to the size and shape from the original treatment plan, respectively. This technique was validated by simulating errors in phantom test deliveries and by comparison between EPID measurements and treatment log files. The method was applied offline to images acquired during the LIGHT Stereotactic Ablative Body Radiotherapy (SABR) clinical trial, where MLC tracking was performed for 17 lung cancer patients. The EPID‐based verification results were subsequently compared to post‐treatment dose reconstruction.ResultsSimulated field location errors were detected during phantom validation tests with an uncertainty of 0.28 mm (parallel to MLC motion) and 0.38 mm (perpendicular), expressed as a root‐mean‐square error (RMSError). For simulated field size errors, the RMSError was 0.47 cm2 and field shape changes were detected for random errors with standard deviation ≥ 2.5 mm. For clinical lung SABR deliveries, field location errors of 1.6 mm (parallel MLC motion) and 4.9 mm (perpendicular) were measured (expressed as a full‐width‐half‐maximum). The mean and standard deviation of the errors in field size and shape were 0.0 ± 0.3 cm2 and 0.3 ± 0.1 (expressed as a translation‐invariant normalized RMS). No correlation was observed between geometric errors during each treatment fraction and dosimetric errors in the reconstructed dose to the target volume for this cohort of patients.ConclusionA system for real‐time delivery verification has been developed for MLC tracking using time‐resolved EPID imaging. The technique has been tested offline in phantom‐based deliveries and clinical patient deliveries and was used to independently verify the geometric accuracy of the MLC during MLC tracking radiotherapy.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Whelan2021,

title = {Magnetic modeling of actively shielded rotating MRI magnets in the presence of environmental steel},

author = {Brendan Whelan and Martino Leghissa and Philipp Amrein and Maxim Zaitsev and Bernhard Heinrich and Rebecca Fahrig and Heiko Rohdjess},

doi = {10.1088/1361-6560/abd010},

issn = {1361-6560},

year  = {2021},

date = {2021-02-21},

journal = {Phys. Med. Biol.},

volume = {66},

number = {4},

publisher = {IOP Publishing},

abstract = {Abstract

               Rotating MRI systems could enable novel integrated medical devices such as MRI-Linacs, MRI-xray-angiography systems, and MRI-proton therapy systems. This work aimed to investigate the feasibility of rotating actively shielded superconducting MRI magnets in the presence of environmental steel—in particular, construction steel in the floor of the installation site. Two magnets were investigated: a 1.0 T split bore magnet, and a 1.5 T closed bore magnet. Each magnet was scaled to emulate field strengths of 0.5, 1.0, and 1.5 T. Finite Element Modeling was used to simulate these magnets in the presence of a 3 × 4 m steel plate located 1250 mm or 1400 mm below the isocenter. There are two possible rotation directions: around the longitudinal (z) axis or around the transverse (x) axis. Each model was solved for rotation angles between 0 and 360° in 30° intervals around each of these axes. For each simulation, a 300 mm DSV was extracted and decomposed into spherical harmonics. For the closed-bore magnet, total induced perturbation for the zero degree rotation angle was 223, 432, and 562 μT peak-to-peak (pk–pk) for the 0.5, 1.0, and 1.5 T models respectively (steel at 1250 mm). For the split-bore magnet, the same numbers were 1477, 16747, and 1766 μT. The substantially higher perturbation for the split-bore magnet can be traced to its larger fringe field. For rotation around the z-axis, total perturbation does not change as a function of angle but is exchanged between different harmonics. For rotation around the x-axis, total perturbation is different at each rotation angle. For the closed bore magnet, maximum perturbations occurred for a 90° rotation around the transverse axis. For the split-bore magnet, the opposite was observed, with the same 90° rotation yielding total perturbation lower than the conventional position. In all cases, at least 95% of the total perturbation was composed of 1st and 2nd order harmonics. The presence of environmental steel poses a major challenge to the realization of an actively shielded rotating superconducting MRI system, requiring some novel form of shimming. Possible shimming strategies are discussed at length.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Booth2021,

title = {MLC tracking for lung SABR is feasible, efficient and delivers high-precision target dose and lower normal tissue dose},

author = {Jeremy Booth and Vincent Caillet and Adam Briggs and Nicholas Hardcastle and Georgios Angelis and Dasantha Jayamanne and Meegan Shepherd and Alexander Podreka and Kathryn Szymura and Doan Trang Nguyen and Per Poulsen and Ricky O'Brien and Benjamin Harris and Carol Haddad and Thomas Eade and Paul Keall},

doi = {10.1016/j.radonc.2020.10.036},

issn = {0167-8140},

year  = {2021},

date = {2021-02-00},

journal = {Radiotherapy and Oncology},

volume = {155},

pages = {131--137},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Buckley2020b,

title = {Measurements of human tolerance to horizontal rotation within an MRI scanner: Towards gantry‐free radiation therapy},

author = {Jarryd G Buckley and Allan “Ben” Smith and Mark Sidhom and Robba Rai and Gary P Liney and Jason A Dowling and Peter E Metcalfe and Lois C Holloway and Paul J Keall},

doi = {10.1111/1754-9485.13130},

issn = {1754-9485},

year  = {2021},

date = {2021-02-00},

journal = {J Med Imag Rad Onc},

volume = {65},

number = {1},

pages = {112--119},

publisher = {Wiley},

abstract = {AbstractIntroductionRecent advances in image guidance and adaptive radiotherapy could enable gantry‐free radiotherapy using patient rotation. Gantry‐free radiotherapy could substantially reduce the cost of radiotherapy systems and facilities. MRI guidance complements a gantry‐free approach because of its ability to visualise soft tissue deformation during rotation. A potential barrier to gantry‐free radiotherapy is patient acceptability, especially when combined with MRI. This study investigates human experiences of horizontal rotation within an MRI scanner.MethodsTen healthy human participants and nine participants previously treated with radiotherapy were rotated within an MRI scanner. Participants' anxiety and motion sickness was assessed before being rotated in 45‐degree increments and paused, representing a multi‐field intensity‐modulated radiotherapy treatment. An MR image was acquired at each 45‐degree angle. Following imaging, anxiety and motion sickness were re‐assessed, followed by a comfort questionnaire and exit interview. The significance of the differences in anxiety and motion sickness pre‐ versus post‐imaging was assessed using Wilcoxon signed‐rank tests. Content analysis was performed on exit interview transcripts.ResultsEight of ten healthy and eight of nine patient participants completed the imaging session. Mean anxiety scores before and after imaging were 7.9/100 and 11.8/100, respectively (P = 0.26), and mean motion sickness scores were 5.3/100 and 13.7/100, respectively (P = 0.02). Most participants indicated likely acceptance of rotation if MRI were to be used in a hypothetical treatment. Physical discomfort was reported to be the biggest concern.ConclusionsHorizontal rotation within an MRI scanner was acceptable for most (17/19) participants.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Buckley2020d,

title = {Measurements of human tolerance to horizontal rotation within an MRI scanner: Towards gantry‐free radiation therapy},

author = {Jarryd G Buckley and Allan “Ben” Smith and Mark Sidhom and Robba Rai and Gary P Liney and Jason A Dowling and Peter E Metcalfe and Lois C Holloway and Paul J Keall},

doi = {10.1111/1754-9485.13130},

issn = {1754-9485},

year  = {2021},

date = {2021-02-00},

journal = {J Med Imag Rad Onc},

volume = {65},

number = {1},

pages = {112--119},

publisher = {Wiley},

abstract = {AbstractIntroductionRecent advances in image guidance and adaptive radiotherapy could enable gantry‐free radiotherapy using patient rotation. Gantry‐free radiotherapy could substantially reduce the cost of radiotherapy systems and facilities. MRI guidance complements a gantry‐free approach because of its ability to visualise soft tissue deformation during rotation. A potential barrier to gantry‐free radiotherapy is patient acceptability, especially when combined with MRI. This study investigates human experiences of horizontal rotation within an MRI scanner.MethodsTen healthy human participants and nine participants previously treated with radiotherapy were rotated within an MRI scanner. Participants' anxiety and motion sickness was assessed before being rotated in 45‐degree increments and paused, representing a multi‐field intensity‐modulated radiotherapy treatment. An MR image was acquired at each 45‐degree angle. Following imaging, anxiety and motion sickness were re‐assessed, followed by a comfort questionnaire and exit interview. The significance of the differences in anxiety and motion sickness pre‐ versus post‐imaging was assessed using Wilcoxon signed‐rank tests. Content analysis was performed on exit interview transcripts.ResultsEight of ten healthy and eight of nine patient participants completed the imaging session. Mean anxiety scores before and after imaging were 7.9/100 and 11.8/100, respectively (P = 0.26), and mean motion sickness scores were 5.3/100 and 13.7/100, respectively (P = 0.02). Most participants indicated likely acceptance of rotation if MRI were to be used in a hypothetical treatment. Physical discomfort was reported to be the biggest concern.ConclusionsHorizontal rotation within an MRI scanner was acceptable for most (17/19) participants.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Booth2021b,

title = {MLC tracking for lung SABR is feasible, efficient and delivers high-precision target dose and lower normal tissue dose},

author = {Jeremy Booth and Vincent Caillet and Adam Briggs and Nicholas Hardcastle and Georgios Angelis and Dasantha Jayamanne and Meegan Shepherd and Alexander Podreka and Kathryn Szymura and Doan Trang Nguyen and Per Poulsen and Ricky O'Brien and Benjamin Harris and Carol Haddad and Thomas Eade and Paul Keall},

doi = {10.1016/j.radonc.2020.10.036},

issn = {0167-8140},

year  = {2021},

date = {2021-02-00},

journal = {Radiotherapy and Oncology},

volume = {155},

pages = {131--137},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Scarpelli2021,

title = {Domain classification and analysis of national institutes of health‐funded medical physics research},

author = {Matthew Scarpelli and Brendan Whelan and Keyvan Farahani},

doi = {10.1002/mp.14469},

issn = {2473-4209},

year  = {2021},

date = {2021-02-00},

journal = {Medical Physics},

volume = {48},

number = {2},

pages = {605--614},

publisher = {Wiley},

abstract = {PurposeThe American Association of Physicists in Medicine (AAPM) previously developed a research database consisting of the National Institutes of Health (NIH) grants that were awarded to its members. The purpose of this report is to classify these NIH grants into various medical physics subdisciplines and analyze the scope of AAPM member research.MethodsFor this report, an algorithm classified grant topics into medical physics research subdisciplines (grants from 2002 to 2019 were analyzed). This algorithm utilized a search for common words and phrases within grant titles, keywords, abstracts, and activity codes to perform the classification. AAPM member grants were compared with non‐AAPM member grants in various relevant subcategories to assess what percentage of these grants was held by AAPM members.ResultsThe percentage of AAPM member grants that included words relating to both imaging and therapy (image‐guided therapy grants) increased from 13% (27/207) in 2002 to 27% (79/293) in 2019. The percentage of AAPM member grants utilizing words relating to artificial intelligence increased from 8% in 2002 to 20% in 2019. From 2002 to 2019, AAPM member grants referenced cancer more than all other diseases combined. The majority of AAPM member grants included words relating to clinical research (81% of grants in 2002 and 99% in 2019). When comparing AAPM member with non‐AAPM member grants it was found that in 2019 AAPM members held a substantial fraction of all NIH grants that referenced stereotactic radiation therapies (41%), radionuclide therapies (10%), brachytherapies (35%), intensity‐modulated radiation therapies (45%), and external beam particle therapies (55%). From 2002 to 2019, the percentage of AAPM membership holding NIH grants decreased for males (3.2% down to 2.3%) and increased for females (0.8% up to 1.3%)ConclusionsThe majority of grants awarded to AAPM members focus on clinical research, which underlies the translational aspect of medical physics and suggests medical physicists are uniquely positioned to help translate new technologies such as artificial intelligence into the clinic. Since 2002, NIH grants awarded to AAPM members have increasingly referenced some form of image‐guided therapy, suggesting opportunities for continued innovation of imaging technologies. A substantial fraction of all radiotherapy‐related research grants were awarded to AAPM members, emphasizing the important role physicists have in developing radiotherapy‐related treatments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Buckley2020,

title = {Pelvic organ motion and dosimetric implications during horizontal patient rotation for prostate radiation therapy},

author = {J. G. Buckley and J. A. Dowling and M. Sidhom and G. P. Liney and R. Rai and P. E. Metcalfe and L. C. Holloway and P. J. Keall},

doi = {10.1002/mp.14579},

issn = {2473-4209},

year  = {2021},

date = {2021-01-00},

journal = {Medical Physics},

volume = {48},

number = {1},

pages = {397--413},

publisher = {Wiley},

abstract = {PurposeGantry‐free radiation therapy systems utilizing patient rotation would be simpler and more cost effective than the conventional gantry‐based systems. Such a system could enable the expansion of radiation therapy to meet global demand and reduce capital costs. Recent advances in adaptive radiation therapy could potentially be applied to correct for gravitational deformation during horizontal patient rotation. This study aims to quantify the pelvic organ motion and the dosimetric implications of horizontal rotation for prostate intensity‐modulated radiation therapy (IMRT) treatments.MethodsEight human participants who previously received prostate radiation therapy were imaged in a clinical magnetic resonance imaging (MRI) scanner using a bespoke patient rotation system (PRS). The patients were imaged every 45 degrees during a full roll rotation (0–360 degrees). Whole pelvic bone, prostate, rectum, and bladder motion were compared to the supine position using dice similarity coefficient (DSC) and mean absolute surface distance (MASD). Prostate centroid motion was compared in the left–right (LR), superior–inferior (SI), and anterior–posterior (AP) direction prior to and following pelvic bone‐guided rigid registration. Seven‐field prostate IMRT treatment plans were generated for each patient rotation angles under three adaption scenarios: No plan adaption, rigid planning target volume (PTV)‐guided alignment to the prostate, and plan re‐optimization. Prostate, rectum, and bladder doses were compared for each adaption scenario.ResultsPelvic bone motion within the PRS of up to 53 mm relative to the supine position was observed for some participants. Internal organ motion was greatest at the 180‐degree PRS couch angle (prone), with prostate centroid motion range < 2 mm LR, 0 mm to 14 mm SI, and −11 mm to 4 mm AP. Rotation with no adaption of the treatment plan resulted in an underdose to the PTV –– in some instances up to 75% (D95%: 78 ± 0.3 Gy at supine to 20 ± 15.0 Gy at the 225‐degree PRS couch angle). Bladder dose was reduced during the rotation by up to 98% (V60 Gy: 15.0 ± 9.4% supine to 0.3 ± 0.5% at the 225‐degree PRS couch angle). In some instances, the rectum dose increased during rotation (V60Gy: 20.0 ± 4.5% supine to 25.0 ± 15.0% at the 135‐degree PRS couch angle). Rigid PTV‐guided alignment resulted in PTV coverage which, though statistically lower (P < 0.05 for all D95% values), was within 1 Gy of the supine plans. Plan re‐optimization resulted in a statistically equivalent PTV coverage compared to the supine plans (P > 0.05 for all D95% metrics and all within ±0.4 Gy). For both rigid PTV‐guided alignment and plan re‐optimization, rectum dose volume metrics were reduced compared to the supine position between the 90‐ and 225‐degree PRS couch angles (P < 0.05). Bladder dose volume metrics were not impacted by rotation.ConclusionPelvic bone and internal organ motion are present during patient rotation. Rigid PTV‐guided alignment to the prostate will be a requirement if prostate IMRT is to be safely delivered using patient rotation. Plan re‐optimization for each PRS couch angle to account for anatomical deformations further improves the PTV coverage.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hewson2020,

title = {Adapting to the motion of multiple independent targets using multileaf collimator tracking for locally advanced prostate cancer: Proof of principle simulation study},

author = {Emily A. Hewson and Yuanyuan Ge and Ricky O'Brien and Stephanie Roderick and Linda Bell and Per R. Poulsen and Thomas Eade and Jeremy T. Booth and Paul J. Keall and Doan T. Nguyen},

doi = {10.1002/mp.14572},

issn = {2473-4209},

year  = {2021},

date = {2021-01-00},

journal = {Medical Physics},

volume = {48},

number = {1},

pages = {114--124},

publisher = {Wiley},

abstract = {PurposeFor patients with locally advanced cancer, multiple targets are treated simultaneously with radiotherapy. Differential motion between targets can compromise the treatment accuracy, yet there are currently no methods able to adapt to independent target motion. This study developed a multileaf collimator (MLC) tracking algorithm for differential motion adaptation and evaluated it in simulated treatments of locally advanced prostate cancer.MethodsA multi‐target MLC tracking algorithm was developed that consisted of three steps: (a) dividing the MLC aperture into two possibly overlapping sections assigned to the prostate and lymph nodes, (b) calculating the ideally shaped MLC aperture as a union of the individually translated sections, and (c) fitting the MLC positions to the ideal aperture shape within the physical constraints of the MLC leaves. The multi‐target tracking method was evaluated and compared with two existing motion management methods: single‐target tracking and no tracking. Treatment simulations of six locally advanced prostate cancer patients with three prostate motion traces were performed for all three motion adaptation methods. The geometric error for each motion adaptation method was calculated using the area of overexposure and underexposure of each field. The dosimetric error was estimated by calculating the dose delivered to the prostate, lymph nodes, bladder, rectum, and small bowel using a motion‐encoded dose reconstruction method.ResultsMulti‐target MLC tracking showed an average improvement in geometric error of 84% compared to single‐target tracking, and 83% compared to no tracking. Multi‐target tracking maintained dose coverage to the prostate clinical target volume (CTV) D98% and planning target volume (PTV) D95% to within 4.8% and 3.9% of the planned values, compared to 1.4% and 0.7% with single‐target tracking, and 20.4% and 31.8% with no tracking. With multi‐target tracking, the node CTV D95%, PTV D90%, and gross tumor volume (GTV) D95% were within 0.3%, 0.6%, and 0.3% of the planned values, compared to 9.1%, 11.2%, and 21.1% for single‐target tracking, and 0.8%, 2.0%, and 3.2% with no tracking. The small bowel V57% was maintained within 0.2% to the plan using multi‐target tracking, compared to 8% and 3.5% for single‐target tracking and no tracking, respectively. Meanwhile, the bladder and rectum V50% increased by up to 13.6% and 5.2%, respectively, using multi‐target tracking, compared to 2.7% and 1.9% for single‐target tracking, and 11.2% and 11.5% for no tracking.ConclusionsA multi‐target tracking algorithm was developed and tracked the prostate and lymph nodes independently during simulated treatments. As the algorithm optimizes for target coverage, tracking both targets simultaneously may increase the dose delivered to the organs at risk.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Buckley2020c,

title = {Pelvic organ motion and dosimetric implications during horizontal patient rotation for prostate radiation therapy},

author = {J. G. Buckley and J. A. Dowling and M. Sidhom and G. P. Liney and R. Rai and P. E. Metcalfe and L. C. Holloway and P. J. Keall},

doi = {10.1002/mp.14579},

issn = {2473-4209},

year  = {2021},

date = {2021-01-00},

journal = {Medical Physics},

volume = {48},

number = {1},

pages = {397--413},

publisher = {Wiley},

abstract = {PurposeGantry‐free radiation therapy systems utilizing patient rotation would be simpler and more cost effective than the conventional gantry‐based systems. Such a system could enable the expansion of radiation therapy to meet global demand and reduce capital costs. Recent advances in adaptive radiation therapy could potentially be applied to correct for gravitational deformation during horizontal patient rotation. This study aims to quantify the pelvic organ motion and the dosimetric implications of horizontal rotation for prostate intensity‐modulated radiation therapy (IMRT) treatments.MethodsEight human participants who previously received prostate radiation therapy were imaged in a clinical magnetic resonance imaging (MRI) scanner using a bespoke patient rotation system (PRS). The patients were imaged every 45 degrees during a full roll rotation (0–360 degrees). Whole pelvic bone, prostate, rectum, and bladder motion were compared to the supine position using dice similarity coefficient (DSC) and mean absolute surface distance (MASD). Prostate centroid motion was compared in the left–right (LR), superior–inferior (SI), and anterior–posterior (AP) direction prior to and following pelvic bone‐guided rigid registration. Seven‐field prostate IMRT treatment plans were generated for each patient rotation angles under three adaption scenarios: No plan adaption, rigid planning target volume (PTV)‐guided alignment to the prostate, and plan re‐optimization. Prostate, rectum, and bladder doses were compared for each adaption scenario.ResultsPelvic bone motion within the PRS of up to 53 mm relative to the supine position was observed for some participants. Internal organ motion was greatest at the 180‐degree PRS couch angle (prone), with prostate centroid motion range < 2 mm LR, 0 mm to 14 mm SI, and −11 mm to 4 mm AP. Rotation with no adaption of the treatment plan resulted in an underdose to the PTV –– in some instances up to 75% (D95%: 78 ± 0.3 Gy at supine to 20 ± 15.0 Gy at the 225‐degree PRS couch angle). Bladder dose was reduced during the rotation by up to 98% (V60 Gy: 15.0 ± 9.4% supine to 0.3 ± 0.5% at the 225‐degree PRS couch angle). In some instances, the rectum dose increased during rotation (V60Gy: 20.0 ± 4.5% supine to 25.0 ± 15.0% at the 135‐degree PRS couch angle). Rigid PTV‐guided alignment resulted in PTV coverage which, though statistically lower (P < 0.05 for all D95% values), was within 1 Gy of the supine plans. Plan re‐optimization resulted in a statistically equivalent PTV coverage compared to the supine plans (P > 0.05 for all D95% metrics and all within ±0.4 Gy). For both rigid PTV‐guided alignment and plan re‐optimization, rectum dose volume metrics were reduced compared to the supine position between the 90‐ and 225‐degree PRS couch angles (P < 0.05). Bladder dose volume metrics were not impacted by rotation.ConclusionPelvic bone and internal organ motion are present during patient rotation. Rigid PTV‐guided alignment to the prostate will be a requirement if prostate IMRT is to be safely delivered using patient rotation. Plan re‐optimization for each PRS couch angle to account for anatomical deformations further improves the PTV coverage.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hewson2020b,

title = {Adapting to the motion of multiple independent targets using multileaf collimator tracking for locally advanced prostate cancer: Proof of principle simulation study},

author = {Emily A. Hewson and Yuanyuan Ge and Ricky O'Brien and Stephanie Roderick and Linda Bell and Per R. Poulsen and Thomas Eade and Jeremy T. Booth and Paul J. Keall and Doan T. Nguyen},

doi = {10.1002/mp.14572},

issn = {2473-4209},

year  = {2021},

date = {2021-01-00},

journal = {Medical Physics},

volume = {48},

number = {1},

pages = {114--124},

publisher = {Wiley},

abstract = {PurposeFor patients with locally advanced cancer, multiple targets are treated simultaneously with radiotherapy. Differential motion between targets can compromise the treatment accuracy, yet there are currently no methods able to adapt to independent target motion. This study developed a multileaf collimator (MLC) tracking algorithm for differential motion adaptation and evaluated it in simulated treatments of locally advanced prostate cancer.MethodsA multi‐target MLC tracking algorithm was developed that consisted of three steps: (a) dividing the MLC aperture into two possibly overlapping sections assigned to the prostate and lymph nodes, (b) calculating the ideally shaped MLC aperture as a union of the individually translated sections, and (c) fitting the MLC positions to the ideal aperture shape within the physical constraints of the MLC leaves. The multi‐target tracking method was evaluated and compared with two existing motion management methods: single‐target tracking and no tracking. Treatment simulations of six locally advanced prostate cancer patients with three prostate motion traces were performed for all three motion adaptation methods. The geometric error for each motion adaptation method was calculated using the area of overexposure and underexposure of each field. The dosimetric error was estimated by calculating the dose delivered to the prostate, lymph nodes, bladder, rectum, and small bowel using a motion‐encoded dose reconstruction method.ResultsMulti‐target MLC tracking showed an average improvement in geometric error of 84% compared to single‐target tracking, and 83% compared to no tracking. Multi‐target tracking maintained dose coverage to the prostate clinical target volume (CTV) D98% and planning target volume (PTV) D95% to within 4.8% and 3.9% of the planned values, compared to 1.4% and 0.7% with single‐target tracking, and 20.4% and 31.8% with no tracking. With multi‐target tracking, the node CTV D95%, PTV D90%, and gross tumor volume (GTV) D95% were within 0.3%, 0.6%, and 0.3% of the planned values, compared to 9.1%, 11.2%, and 21.1% for single‐target tracking, and 0.8%, 2.0%, and 3.2% with no tracking. The small bowel V57% was maintained within 0.2% to the plan using multi‐target tracking, compared to 8% and 3.5% for single‐target tracking and no tracking, respectively. Meanwhile, the bladder and rectum V50% increased by up to 13.6% and 5.2%, respectively, using multi‐target tracking, compared to 2.7% and 1.9% for single‐target tracking, and 11.2% and 11.5% for no tracking.ConclusionsA multi‐target tracking algorithm was developed and tracked the prostate and lymph nodes independently during simulated treatments. As the algorithm optimizes for target coverage, tracking both targets simultaneously may increase the dose delivered to the organs at risk.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Caillet2020,

title = {Geometric uncertainty analysis of MLC tracking for lung SABR},

author = {Vincent Caillet and Benjamin Zwan and Adam Briggs and Nicholas Hardcastle and Kathryn Szymura and Alexander Prodreka and Ricky O’Brien and Ben E Harris and Peter Greer and Carol Haddad and Dasantha Jayamanne and Thomas Eade and Jeremy Booth and Paul Keall},

doi = {10.1088/1361-6560/abb0c6},

issn = {1361-6560},

year  = {2020},

date = {2020-12-07},

journal = {Phys. Med. Biol.},

volume = {65},

number = {23},

publisher = {IOP Publishing},

abstract = {Abstract

               

                  Purpose. The purpose of this work was to report on the geometric uncertainty for patients treated with multi-leaf collimator (MLC) tracking for lung SABR to verify the accuracy of the system. Methods. Seventeen patients were treated as part of the MLC tracking for lung SABR clinical trial using electromagnetic beacons implanted around the tumor acting as a surrogate for target motion. Sources of uncertainties evaluated in the study included the surrogate-target positional uncertainty, the beam-surrogate tracking uncertainty, the surrogate localization uncertainty, and the target delineation uncertainty. Probability density functions (PDFs) for each source of uncertainty were constructed for the cohort and each patient. The total PDFs was computed using a convolution approach. The 95% confidence interval (CI) was used to quantify these uncertainties. Results. For the cohort, the surrogate-target positional uncertainty 95% CIs were ±2.5 mm (−2.0/3.0 mm) in left-right (LR), ±3.0 mm (−1.6/4.5 mm) in superior–inferior (SI) and ±2.0 mm (−1.8/2.1 mm) in anterior–posterior (AP). The beam-surrogate tracking uncertainty 95% CIs were ±2.1 mm (−2.1/2.1 mm) in LR, ±2.8 mm (−2.8/2.7 mm) in SI and ±2.1 mm (−2.1/2.0 mm) in AP directions. The surrogate localization uncertainty minimally impacted the total PDF with a width of ±0.6 mm. The target delineation uncertainty distribution 95% CIs were ±5.4 mm. For the total PDF, the 95% CIs were ±5.9 mm (−5.8/6.0 mm) in LR, ±6.7 mm (−5.8/7.5 mm) in SI and ±6.0 mm (−5.5/6.5 mm) in AP. Conclusion. This work reports the geometric uncertainty of MLC tracking for lung SABR by accounting for the main sources of uncertainties that occurred during treatment. The overall geometric uncertainty is within ±6.0 mm in LR and AP directions and ±6.7 mm in SI. The dominant uncertainty was the target delineation uncertainty. This geometric analysis helps put into context the range of uncertainties that may be expected during MLC tracking for lung SABR (ClinicalTrials.gov registration number: NCT02514512).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kurz2020,

title = {Medical physics challenges in clinical MR-guided radiotherapy},

author = {Christopher Kurz and Giulia Buizza and Guillaume Landry and Florian Kamp and Moritz Rabe and Chiara Paganelli and Guido Baroni and Michael Reiner and Paul J. Keall and Cornelis A. T. van den Berg and Marco Riboldi},

doi = {10.1186/s13014-020-01524-4},

issn = {1748-717X},

year  = {2020},

date = {2020-12-00},

journal = {Radiat Oncol},

volume = {15},

number = {1},

publisher = {Springer Science and Business Media LLC},

abstract = {AbstractThe integration of magnetic resonance imaging (MRI) for guidance in external beam radiotherapy has faced significant research and development efforts in recent years. The current availability of linear accelerators with an embedded MRI unit, providing volumetric imaging at excellent soft tissue contrast, is expected to provide novel possibilities in the implementation of image-guided adaptive radiotherapy (IGART) protocols. This study reviews open medical physics issues in MR-guided radiotherapy (MRgRT) implementation, with a focus on current approaches and on the potential for innovation in IGART.Daily imaging in MRgRT provides the ability to visualize the static anatomy, to capture internal tumor motion and to extract quantitative image features for treatment verification and monitoring. Those capabilities enable the use of treatment adaptation, with potential benefits in terms of personalized medicine. The use of online MRI requires dedicated efforts to perform accurate dose measurements and calculations, due to the presence of magnetic fields. Likewise, MRgRT requires dedicated quality assurance (QA) protocols for safe clinical implementation.Reaction to anatomical changes in MRgRT, as visualized on daily images, demands for treatment adaptation concepts, with stringent requirements in terms of fast and accurate validation before the treatment fraction can be delivered. This entails specific challenges in terms of treatment workflow optimization, QA, and verification of the expected delivered dose while the patient is in treatment position. Those challenges require specialized medical physics developments towards the aim of fully exploiting MRI capabilities. Conversely, the use of MRgRT allows for higher confidence in tumor targeting and organs-at-risk (OAR) sparing.The systematic use of MRgRT brings the possibility of leveraging IGART methods for the optimization of tumor targeting and quantitative treatment verification. Although several challenges exist, the intrinsic benefits of MRgRT will provide a deeper understanding of dose delivery effects on an individual basis, with the potential for further treatment personalization.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Liu2020,

title = {First experimental investigation of simultaneously tracking two independently moving targets on an MRI‐linac using real‐time MRI and MLC tracking},

author = {Paul Z. Y. Liu and Bing Dong and Doan Trang Nguyen and Yuanyuan Ge and Emily A. Hewson and David E. J. Waddington and Ricky O'Brien and Gary P. Liney and Paul J. Keall},

doi = {10.1002/mp.14536},

issn = {2473-4209},

year  = {2020},

date = {2020-12-00},

journal = {Medical Physics},

volume = {47},

number = {12},

pages = {6440--6449},

publisher = {Wiley},

abstract = {PurposeHigh quality radiotherapy is challenging in cases where multiple targets with independent motion are simultaneously treated. A real‐time tumor tracking system that can simultaneously account for the motion of two targets was developed and characterized.MethodsThe multitarget tracking system was implemented on a magnetic resonance imaging (MRI)‐linac and utilized multi‐leaf collimator (MLC) tracking to adapt the radiation beam to phantom targets reproducing motion with prostate and lung motion traces. Multitarget tracking consisted of three stages: (a) pretreatment aperture segmentation where the treatment aperture was divided into segments corresponding to each target, (b) MR imaging where the positions of the two targets were localized, and (c) MLC tracking where an updated treatment aperture was calculated. Electronic portal images (EPID) acquired during irradiation were analyzed to characterize geometric uncertainty and tracking latency.ResultsMultitarget MLC tracking effectively accounted for the motion of both targets during treatment. The root‐mean‐square error between the centers of the targets and the centers of the corresponding MLC leaves were reduced from 5.5 mm without tracking to 2.7 mm with tracking for lung motion traces and reduced from 4.2 to 1.4 mm for prostate motion traces. The end‐to‐end latency of tracking was measured to be 328 ± 44 ms.ConclusionsWe have demonstrated the first experimental implementation of MLC tracking for multiple targets having independent motion. This technology takes advantage of the imaging capabilities of MRI‐linacs and would allow treatment margins to be reduced in cases where multiple targets are simultaneously treated.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Shi2020,

title = {Experimental evaluation of the dosimetric impact of intrafraction prostate rotation using film measurement with a 6DoF robotic arm},

author = {Kehuan Shi and Andrew Dipuglia and Jeremy Booth and Saree Alnaghy and Andre Kyme and Paul Keall and Doan Trang Nguyen},

doi = {10.1002/mp.14502},

issn = {2473-4209},

year  = {2020},

date = {2020-12-00},

journal = {Medical Physics},

volume = {47},

number = {12},

pages = {6068--6076},

publisher = {Wiley},

abstract = {PurposeTumor motion during radiotherapy can cause a reduction in target dose coverage and an increase in healthy tissue exposure. Tumor motion is not strictly translational and often exhibits complex six degree‐of‐freedom (6DoF) translational and rotational motion. Although the dosimetric impact of prostate tumor translational motion is well investigated, the dosimetric impact of 6DoF motion has only been studied with simulations or dose reconstruction. This study aims to experimentally quantify the dose error caused by 6DoF motion. The experiment was designed to test the hypothesis that 6DoF motion would cause larger dose errors than translational motion alone through gamma analyses of two‐dimensional film measurements.MethodsFour patient‐measured intrafraction prostate motion traces and four VMAT 7.25 Gy/Fx SBRT treatment plans were selected for the experiment. The traces represented typical motion patterns, including small‐angle rotations (<4°), transient movement, persistent excursion, and erratic rotations (>6°). Gafchromic film was placed inside a custom‐designed phantom, held by a high‐precision 6DoF robotic arm for dose measurements in the coronal plane during treatment delivery. For each combination of the motion trace and treatment plan, two film measurements were made, one with 6DoF motion and the other with the three‐dimensional (3D) translation components of the same trace. A gamma pass rate criteria of 2% relative dose/2 mm distance‐to‐agreement was used in this study and evaluated for each measurement with respect to the static reference film. Two test thresholds, 90% and 50% of the reference dose, were applied to investigate the difference in dose coverage for the PTV region and surrounding areas, respectively. The hypothesis was tested using a Wilcoxon signed‐rank test.ResultsFor each of the 16 plan and motion trace pairs, a reduction in the gamma pass rate was observed for 6DoF motion compared with 3D translational motion. With 90% gamma‐test threshold, the reduction was 5.8% ± 7.1% (P < 0.01). With 50% gamma‐test threshold, the reduction was 4.1% ± 4.8% (P < 0.01).ConclusionFor the first time, the dosimetric impact of intrafraction prostate rotation during SBRT treatment was measured experimentally. The experimental results support the hypothesis that 6DoF tumor motion causes higher dose error than translation motion alone.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{DeDeene2020,

title = {Towards real-time 4D radiation dosimetry on an MRI-Linac},

author = {Y De Deene and M Wheatley and B Dong and N Roberts and U Jelen and D Waddington and G Liney},

doi = {10.1088/1361-6560/abb9f7},

issn = {1361-6560},

year  = {2020},

date = {2020-11-21},

journal = {Phys. Med. Biol.},

volume = {65},

number = {22},

publisher = {IOP Publishing},

abstract = {Abstract

               4D radiation dosimetry using a highly radiation-sensitive polymer gel dosimeter with real-time quantitative magnetic resonance imaging (MRI) readout is presented as a technique to acquire the accumulated radiation dose distribution during image-guided radiotherapy on an MRI-Linac. Optimized T

                  2-weighted Turbo-Spin-Echo (TSE) scans are converted into quantitative ΔR

                  2 maps and subsequently to radiation dose maps.

               The concept of temporal uncertainty is introduced as a metric of effective temporal resolution. A mathematical framework is presented to optimize the echo time of the TSE sequence in terms of dose resolution, and the trade-off between temporal resolution and dose resolution is discussed. The current temporal uncertainty achieved with the MAGAT gel dosimeter on a 1 T MRI-Linac is 3.8 s which is an order of magnitude better than what has been achieved until now.

               The potential of real-time 4D radiation dosimetry in a theragnostic MRI-Linac is demonstrated for two scenarios: an irradiation with three coplanar beams on a head phantom and a dynamic arc treatment on a cylindrical gel phantom using a rotating couch. The dose maps acquired on the MRI-Linac are compared with a treatment plan and with dose maps acquired on a clinical 3 T MRI scanner. 3D gamma map evaluations for the different modalities are provided. While the presented method demonstrates the potential of gel dosimetry for tracking the dose delivery during radiotherapy in 4D, a shortcoming of the MAGAT gel dosimeter is a retarded dose response.

               The effect of non-ideal radiofrequency pulses resulting from limitations in the specific absorption rate or B1-field inhomogeneity on the TSE acquired ΔR

                  2 values is analysed experimentally and by use of computational modelling with a Bloch simulator.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Reynolds2020,

title = {Toward improved 3D carotid artery imaging with Adaptive CaRdiac cOne BEAm computed Tomography (ACROBEAT)},

author = {Tess Reynolds and Owen Dillon and Joseph Prinable and Brendan Whelan and Paul J. Keall and Ricky T. O’Brien},

doi = {10.1002/mp.14462},

issn = {2473-4209},

year  = {2020},

date = {2020-11-00},

journal = {Medical Physics},

volume = {47},

number = {11},

pages = {5749--5760},

publisher = {Wiley},

abstract = {PurposeInterventional treatments of aneurysms in the carotid artery are increasingly being supplemented with three‐dimensional (3D) x‐ray imaging. The 3D imaging provides additional information on device sizing and stent malapposition during the procedure. Standard 3D x‐ray image acquisition is a one‐size fits all model, exposing patients to additional radiation and results in images that may have cardiac‐induced motion blur around the artery. Here, we investigate the potential of a novel dynamic imaging technique Adaptive CaRdiac cOne BEAm computed Tomography (ACROBEAT) to personalize image acquisition by adapting the gantry velocity and projection rate in real‐time to changes in the patient’s electrocardiogram (ECG) trace.MethodsWe compared the total number of projections acquired, estimated carotid artery widths and image quality between ACROBEAT and conventional (single rotation fixed gantry velocity and acquisition rate, no ECG‐gating) scans in a simulation study and a proof‐of‐concept physical phantom experimental study. The simulation study dataset consisted of an XCAT digital software phantom programmed with five patient‐measured ECG traces and artery motion curves. The ECG traces had average heart rates of 56, 64, 76, 86, and 100 bpm. To validate the concept experimentally, we designed and manufactured the physical phantom from an 8‐mm diameter silicon rubber tubing cast into Phytagel. An artery motion curve and the ECG trace with an average heart rate of 56 bpm was passed through the phantom. To implement ACROBEAT on the Siemens ARTIS pheno angiography system for the proof‐of‐concept experimental study, the Siemens Test Automation Control System was used. The total number of projections acquired and estimated carotid artery widths were compared between the ACROBEAT and conventional scans. As the ground truth was available for the simulation studies, the image quality metrics of Root Mean Square Error (RMSE) and Structural Similarity Index (SSIM) were also utilized to assess image quality.ResultsIn the simulation study, on average, ACROBEAT reduced the number of projections acquired by 63%, reduced carotid width estimation error by 65%, reduced RMSE by 11% and improved SSIM by 27% compared to conventional scans. In the proof‐of‐concept experimental study, ACROBEAT enabled a 60% reduction in the number of projections acquired and reduced carotid width estimation error by 69% compared to a conventional scan.ConclusionA simulation and proof‐of‐concept experimental study was completed applying a novel dynamic imaging protocol, ACROBEAT, to imaging the carotid artery. The ACROBEAT results showed significantly improved image quality with fewer projections, offering potential applications to intracranial interventional procedures negatively affected by cardiac motion.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hewson2020c,

title = {Is multileaf collimator tracking or gating a better intrafraction motion adaptation strategy? An analysis of the TROG 15.01 stereotactic prostate ablative radiotherapy with KIM (SPARK) trial},

author = {Emily A Hewson and Doan T Nguyen and Ricky O'Brien and Per R Poulsen and Jeremy T Booth and Peter Greer and Thomas Eade and Andrew Kneebone and George Hruby and Trevor Moodie and Amy J Hayden and Sandra L Turner and Nicholas Hardcastle and Shankar Siva and Keen Hun Tai and Jarad Martin and Paul J Keall},

doi = {10.1016/j.radonc.2020.08.010},

issn = {0167-8140},

year  = {2020},

date = {2020-10-00},

journal = {Radiotherapy and Oncology},

volume = {151},

pages = {234--241},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kueng2020,

title = {Towards MR-guided electron therapy: Measurement and simulation of clinical electron beams in magnetic fields},

author = {R. Kueng and B.M. Oborn and N.F. Roberts and T. Causer and M.F.M. Stampanoni and P. Manser and P.J. Keall and M.K. Fix},

doi = {10.1016/j.ejmp.2020.09.001},

issn = {1120-1797},

year  = {2020},

date = {2020-10-00},

journal = {Physica Medica},

volume = {78},

pages = {83--92},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dillon2020,

title = {Evaluating reconstruction algorithms for respiratory motion guided acquisition},

author = {Owen Dillon and Paul J Keall and Chun-Chien Shieh and Ricky T O’Brien},

doi = {10.1088/1361-6560/ab98d3},

issn = {1361-6560},

year  = {2020},

date = {2020-09-07},

journal = {Phys. Med. Biol.},

volume = {65},

number = {17},

publisher = {IOP Publishing},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Waddington2020,

title = {High-sensitivity in vivo contrast for ultra-low field magnetic resonance imaging using superparamagnetic iron oxide nanoparticles},

author = {David E. J. Waddington and Thomas Boele and Richard Maschmeyer and Zdenka Kuncic and Matthew S. Rosen},

doi = {10.1126/sciadv.abb0998},

issn = {2375-2548},

year  = {2020},

date = {2020-07-17},

journal = {Sci. Adv.},

volume = {6},

number = {29},

publisher = {American Association for the Advancement of Science (AAAS)},

abstract = {Superparamagnetic nanoparticles will boost image contrast on portable MRI scanners operating at low magnetic fields.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Keall2020,

title = {Real-Time Image Guided Ablative Prostate Cancer Radiation Therapy: Results From the TROG 15.01 SPARK Trial},

author = {Paul Keall and Doan Trang Nguyen and Ricky O'Brien and Emily Hewson and Helen Ball and Per Poulsen and Jeremy Booth and Peter Greer and Perry Hunter and Lee Wilton and Regina Bromley and John Kipritidis and Thomas Eade and Andrew Kneebone and George Hruby and Trevor Moodie and Amy Hayden and Sandra Turner and Sankar Arumugam and Mark Sidhom and Nicholas Hardcastle and Shankar Siva and Keen-Hun Tai and Val Gebski and Jarad Martin},

doi = {10.1016/j.ijrobp.2020.03.014},

issn = {0360-3016},

year  = {2020},

date = {2020-07-00},

journal = {International Journal of Radiation Oncology*Biology*Physics},

volume = {107},

number = {3},

pages = {530--538},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Dunbar2020,

title = {Optimising lung imaging for cancer radiation therapy},

author = {Michelle Dunbar and Ricky O’Brien and Gary Froyland},

doi = {10.1016/j.ejor.2019.10.020},

issn = {0377-2217},

year  = {2020},

date = {2020-05-00},

journal = {European Journal of Operational Research},

volume = {282},

number = {3},

pages = {1038--1052},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Morton2020,

title = {Reducing 4D CT imaging artifacts at the source: first experimental results from the respiratory adaptive computed tomography (REACT) system},

author = {Natasha Morton and Jonathan Sykes and Jeffrey Barber and Christian Hofmann and Paul Keall and Ricky O’Brien},

doi = {10.1088/1361-6560/ab7abe},

issn = {1361-6560},

year  = {2020},

date = {2020-04-01},

journal = {Phys. Med. Biol.},

volume = {65},

number = {7},

publisher = {IOP Publishing},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Boele2020,

title = {Tailored nanodiamonds for hyperpolarized 

C13

 MRI},

author = {T. Boele and D. E. J. Waddington and T. Gaebel and E. Rej and A. Hasija and L. J. Brown and D. R. McCamey and D. J. Reilly},

doi = {10.1103/physrevb.101.155416},

issn = {2469-9969},

year  = {2020},

date = {2020-04-00},

journal = {Phys. Rev. B},

volume = {101},

number = {15},

publisher = {American Physical Society (APS)},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Poulsen2020,

title = {Simulated multileaf collimator tracking for stereotactic liver radiotherapy guided by kilovoltage intrafraction monitoring: Dosimetric gain and target overdose trends},

author = {Per R. Poulsen and Ghulam Murtaza and Esben S. Worm and Thomas Ravkilde and Ricky O'Brien and Cai Grau and Morten Høyer and Paul Keall},

doi = {10.1016/j.radonc.2019.11.008},

issn = {0167-8140},

year  = {2020},

date = {2020-03-00},

journal = {Radiotherapy and Oncology},

volume = {144},

pages = {93--100},

publisher = {Elsevier BV},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jelen2020,

title = {Dosimetric Optimization and Commissioning of a High Field Inline MRI-Linac},

author = {Urszula Jelen and Bin Dong and Jarrad Begg and Natalia Roberts and Brendan Whelan and Paul Keall and Gary Liney},

doi = {10.3389/fonc.2020.00136},

issn = {2234-943X},

year  = {2020},

date = {2020-02-14},

journal = {Front. Oncol.},

volume = {10},

publisher = {Frontiers Media SA},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mueller2020,

title = {The first prospective implementation of markerless lung target tracking in an experimental quality assurance procedure on a standard linear accelerator},

author = {Marco Mueller and Reza Zolfaghari and Adam Briggs and Hugo Furtado and Jeremy Booth and Paul Keall and Doan Nguyen and Ricky O’Brien and Chun-Chien Shieh},

doi = {10.1088/1361-6560/ab5d8b},

issn = {1361-6560},

year  = {2020},

date = {2020-01-01},

journal = {Phys. Med. Biol.},

volume = {65},

number = {2},

publisher = {IOP Publishing},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hindley2019,

title = {Real‐time direct diaphragm tracking using kV imaging on a standard linear accelerator},

author = {Nicholas Hindley and Paul Keall and Jeremy Booth and Chun‐Chien Shieh},

doi = {10.1002/mp.13738},

issn = {2473-4209},

year  = {2019},

date = {2019-10-00},

journal = {Medical Physics},

volume = {46},

number = {10},

pages = {4481--4489},

publisher = {Wiley},

abstract = {PurposeAs the predominant driver of respiratory motion, the diaphragm represents a key surrogate for motion management during the irradiation of thoracic cancers. Existing approaches to diaphragm tracking often produce phase‐based estimates, suffer from lateral side failures or are not executable in real‐time. In this paper, we present an algorithm that continuously produces real‐time estimates of three‐dimensional (3D) diaphragm position using kV images acquired on a standard linear accelerator.MethodsPatient‐specific 3D diaphragm models were generated via automatic segmentation on end‐exhale four‐dimensional‐computed tomography (4D‐CT) images. The estimated trajectory of diaphragmatic motion, referred to as the principal motion vector, was obtained by registering end‐exhale to end‐inhale 4D‐CT images. Two‐dimensional (2D) diaphragm masks were generated by forward‐projecting 3D models over the complement of angles spanned during kV image acquisition. For each kV image, diaphragm position was determined by shifting angle‐matched 2D masks along the principal motion vector and selecting the position of highest contrast on a vertical difference image. Retrospective analysis was performed using 22 cone beam CT (CBCT) image sequences for six lung cancer patients across two datasets. Given the current lack of objective ground truth for diaphragm position, our algorithm was evaluated by examining its ability to track implanted markers. Simple linear regression was used to construct 3D marker motion models and estimation errors were computed as the difference between estimated and ground truth marker positions. Additionally, Pearson correlation coefficients were used to characterize diaphragm‐marker correlation.ResultsThe mean ± standard deviation of the estimation errors across all image sequences was −0.1 ± 0.7 mm, −0.1 ± 1.8 mm and 0.2 ± 1.4 mm in the LR, SI, and AP directions respectively. The 95th percentile of the absolute errors ranged over 0.5–3.1 mm, 1.6–6.7 mm, and 1.2–4.0 mm in the LR, SI, and AP directions, respectively. The mean ± standard deviation of diaphragm‐marker correlations over all image sequences was −0.07 ± 0.57, 0.67 ± 0.49, and 0.29 ± 0.52 in the LR, SI, and AP directions, respectively. Diaphragm‐marker correlation was observed to be highly dependent on marker position. Mean correlation along the SI axis ranged over 0.91–0.93 for markers situated in the lower lobes of the lung, while correlations ranging over −0.51–0.79 were observed for markers situated in the upper and middle lobes.ConclusionThis work advances a new approach to real‐time direct diaphragm tracking in realistic treatment scenarios. By achieving continuous estimates of diaphragmatic motion, the proposed method has applications for both markerless tumor tracking and respiratory binning in 4D‐CBCT.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maxim2019,

title = {FLASH radiotherapy: Newsflash or flash in the pan?},

author = {Peter G. Maxim and Paul Keall and Jing Cai},

doi = {10.1002/mp.13685},

issn = {2473-4209},

year  = {2019},

date = {2019-10-00},

journal = {Medical Physics},

volume = {46},

number = {10},

pages = {4287--4290},

publisher = {Wiley},

keywords = {},

pubstate = {published},

tppubtype = {article}

}