The Australian MRI-Linac Program
The Australian MRI-linac program is a 16 million dollar project to build a Magnetic Resonance Imaging (MRI) device combined with a Linear Accelerator, which is used to treat cancer using radiotherapy. The goal of the project is to develop next generation cancer therapy equipment, in which changing patient anatomy and physiology can be seen during treatment. This will dramatically improve the accuracy of radiotherapy, directly improving outcomes for cancer patients. The program is driven by the research collaboration of the ACRF Image X Institute, the Ingham Institute for Applied Medical Research in Western Sydney, and the Centre for Medical Diagnostic Technologies at the University of Queensland. The Australian MRI-linac program is led by Professor Paul Keall.
(Video courtesy of the Ingham Institute)
Benefits and challenges
An MRI/linear accelerator has a number of benefits compared to existing image guidance technology.
- Excellent soft tissue contrast
- No imaging dose
- 3D Volumetric data
- No fiducial markers
However, combining an MRI with a Linear accelerator is a momentous engineering challenge. MRI utilises strong magnetic fields to form images; these fields will influence many aspects of normal Linac operation. In turn, the presence of the linear accelerator interferes with the MRI image acquisition process.
Through the Australian MRI-Linac Program, we plan to overcome these challenges and develop a new cancer radiotherapy system that can image tumours as they move within the body, and target the radiation beam to follow this motion. Ultimately, we expect that the MRI-Linac will improve tumour control and cancer survival, whilst reducing the side effects from radiation therapy, leading to an improved quality of life for cancer patients.
Even beyond the realms of cancer treatment, the MRI-Linac could hold high therapeutic potential – we are also investigating the potential use of MRI-guided radiotherapy to treat heart rhythm disorders.
One of the main problems in conventional radiotherapy is that tumours and their surrounding organs move around during and between treatments due to breathing, digestion and other physiological processes. This can result in the tumour receiving less radiation than was intended, or the healthy tissue receiving more. This in turn can decrease the efficacy of radiotherapy, whilst increasing the detrimental side effects.
In order to rectify this effect, image guidance in radiotherapy is becoming increasingly common. Image guidance refers to imaging the patient between or during treatments in order to obtain information about any anatomical changes. There has been a steadily increasing uptake of image guidance techniques in the clinic demonstrating the efficacy of such techniques. However, current techniques suffer from a number of shortcomings, such as:
- Poor soft tissue contrast – this can make it difficult to visualise the tumour from its surroundings
- Secondary imaging dose – Imaging dose can result in non negligible increase in secondary cancer riskIn turn, this limits how often some techniques can be utilised.
- Reliance on fiducial markers – Some techniques require the surgical insertion of a number of small metallic markers
- Assumption of correlation between surface anatomy and internal anatomy – Some techniques use information about movement of the patient surface to infer information about the internal anatomy. This assumes a correlation which may or may not exist.
(Image courtesy of the Ingham Institute)
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- Paganelli C, Portoso S, Garau N, Meschini G, Via R, Buizza G, Keall P, Riboldi M, Baroni G. Time-resolved volumetric MRI in MRI-guided radiotherapy: an in silico comparative analysis. Phys Med Biol. 2019 Sep 19;64(18):185013. doi: 10.1088/1361-6560/ab33e5. [More Information]
- Print ISBN 978-3-030-14441-8. Online ISBN 978-3-030-14442-5 [More Information]
MRI Linac Systems. In: Liney G., van der Heide U. (eds) MRI for Radiotherapy. Springer, Cham. https://doi.org/10.1007/978-3-030-14442-5_10.
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- Lee D, Kim S, Palta J, Lewis B, Keall P, Kim T. A retrospective 4D-MRI based on 2D diaphragm profiles for lung cancer patients. J Med Imaging Radiat Oncol. 2019 Jun;63(3):360-369. doi: 10.1111/1754-9485.12877. Epub 2019 Apr 1. [More Information]
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- Paganelli C, Kipritidis J, Lee D, Baroni G, Keall P, Riboldi M. Image-based retrospective 4D MRI in external beam radiotherapy: A comparative study with a digital phantom. Phys Med Biol. 2018 Jul 27;63(15):155012. doi: 10.1088/1361-6560/aaceca [More Information]
- Liney GP, Dong B, Weber E, Rai R, Destruel A, Garcia-Alvarez R, Manton DJ, Jelen U, Zhang K, Barton M, Keall P, Crozier S. Imaging performance of a dedicated radiation transparent RF coil on a 1.0 Tesla inline MRI-linac. Phys Med Biol. 2018 Jun 25;63(13):135005. doi: 10.1088/1361-6560/aac813.[More Information]
- Paganelli C, Lee D, Kipritidis J, Whelan B, Greer PB, Baroni G, Riboldi M,
Keall P. Feasibility study on 3D image reconstruction from 2D orthogonal cine-MRI for MRI-guided radiotherapy. J Med Imaging Radiat Oncol. 2018 Jun;62(3):389-400. doi:10.1111/1754-9485.12713. [More Information]
- Liney GP, Dong B, Weber E, Rai R, Destruel A, Garcia-Alvarez R, Manton D, Jelen U, Zhang K, Barton M, Keall PJ, Crozier S. Imaging performance of a dedicated radiation transparent RF coil on a 1.0 Tesla inline MRI-linac. Phys Med Biol. 2018 May 25. doi:10.1088/1361-6560/aac813. [More Information]
- Paganelli C, Kipritidis J, Lee D, Baroni G, Keall P, Riboldi M. Image-based retrospective 4D MRI in external beam radiotherapy: A comparative study with a digital phantom. Med Phys. 2018 May 14. doi:10.1002/mp.12965. [More Information]
- Whelan, B., Kolling, S., Oborn, B., Keall, P. (2018) Passive magnetic shielding in MRI-Linac systems. Physics in Medicine & Biology, 63(7), 075-008. [More Information]
- Oborn BM, Dowdell S, Metcalfe PE, Crozier S, Mohan R, Keall PJ. Future of medical physics: Real-time MRI-guided proton therapy.Med Phys. 2017 Aug;44(8):e77-e90. doi: 10.1002/mp.12371[More Information]
- Whelan, B., Liney, G., Dowling, J., Rai, R., Holloway, L., McGarvie, L., Feain, I., Barton, M., Berry, M., Wilkins, R., Keall, P. (2017). An MRI-compatible patient rotation system – design, construction, and first organ deformation results. Medical Physics, 44(2), 581-588. [More Information]
- Rai, R., Kumar, S., Batumalai, V., Elwadia, D., Ohanessian, L., Juresic, E., Cassapi, L., Vinod, S., Holloway, L., Keall, P., et al (2017). The integration of MRI in radiation therapy: collaboration of radiographers and radiation therapists. Journal of Medical Radiation Sciences, 64(1), 61-68. [More Information]
- Whelan, B., Gierman, S., Holloway, L., Schmerge, J., Keall, P., Fahrig, R. (2016). A novel electron accelerator for MRI-Linac radiotherapy. Medical Physics, 43(3), 1285-1294. [More Information]
- Seregni, M., Paganelli, C., Lee, D., Greer, P., Baroni, G., Keall, P., Riboldi, M. (2016). Motion prediction in MRI-guided radiotherapy based on interleaved orthogonal cine-MRI. Physics in Medicine and Biology, 61(2), 872-887. [More Information]
- Whelan, B., Holloway, L., Constantin, D., Oborn, B., Bazalova-Carter, M., Fahrig, R., Keall, P. (2016). Performance of a clinical gridded electron gun in magnetic fields: Implications for MRI-linac therapy. Medical Physics, 43(11), 5903-5914. [More Information]
- Ipsen, S., Blanck, O., Lowther, N., Liney, G., Rai, R., Bode, F., Dunst, J., Schweikard, A., Keall, P. (2016). Towards real-time MRI-guided 3D localization of deforming targets for non-invasive cardiac radiosurgery. Physics in Medicine and Biology, 61(22), 7848-7863. [More Information]
- Oborn, B., Dowdell, S., Metcalfe, P., Crozier, S., Mohan, R., Keall, P. (2015). Proton beam deflection in MRI fields: Implications for MRI-guided proton therapy. Medical Physics, 42(5), 2113-2124. [More Information]
- Paganelli, C., Lee, D., Greer, P., Baroni, G., Riboldi, M., Keall, P. (2015). Quantification of lung tumor rotation with automated landmark extraction using orthogonal cine MRI images. Physics in Medicine and Biology, 60(18), 7165-7178. [More Information]
- Oborn, B., Ge, Y., Hardcastle, N., Metcalfe, P., Keall, P. (2015). WE-G-BRD-05: Inline Magnetic Fields Enhance Tumor Dose for Small Lung Cancers. Medical Physics, 42(6), 3689. [More Information]
- Constantin, D., Holloway, L., Keall, P., Fahrig, R. (2014). A novel electron gun for inline MRI-linac configurations. Medical Physics, 41(2), 1-10. [More Information]
- Lee, D., Pollock, S., Whelan, B., Keall, P., Kim, T. (2014). Dynamic keyhole: A novel method to improve MR images in the presence of respiratory motion for real-time MRI. Medical Physics, 41(7), 1-8. [More Information]
- Oborn, B., Kolling, S., Metcalfe, P., Crozier, S., Litzenberg, D., Keall, P. (2014). Electron contamination modeling and reduction in a 1 T open bore inline MRI-linac system. Medical Physics, 41(5), 051708-1-051708-15. [More Information]
- Sawant, A., Keall, P., Butts Pauly, K., Alley, M., Vasanawala, S., Loo, B., Hinkle, J., Joshi, S. (2014). Investigating the feasibility of rapid MRI for image-guided motion management in lung cancer radiotherapy. BioMed Research International, 2014, 1-7. [More Information]
- Ipsen, S., Blanck, O., Oborn, B., Bode, F., Liney, G., Hunold, P., Rades, D., Schweikard, A., Keall, P. (2014). Radiotherapy beyond cancer: Target localization in real-time MRI and treatment planning for cardiac radiosurgery. Medical Physics, 41(12), 1-8. [More Information]
- Keall, P., Barton, M., Crozier, S. (2014). The Australian Magnetic Resonance Imaging-Linac Program. Seminars in Radiation Oncology, 24(3), 203-206. [More Information]
- Kolling, S., Oborn, B., Keall, P. (2013). Impact of the MLC on the MRI field distortion of a prototype MRI-linac. Medical Physics, 40(12), 121705-1-121705-10. [More Information]
- Constantin, D., Fahrig, R., Keall, P. (2011). A study of the effect of in-line and perpendicular magnetic fields on beam characteristics of electron guns in medical linear accelerators. Medical Physics, 38(7), 4174-4185. [More Information]