Magnetic resonance imaging (MRI) guided radiotherapy for prostate cancer

Abstract

Radiotherapy to the prostate involves increasingly sophisticated delivery techniques and changing fractionation schedules. Magnetic resonance imaging (MRI) guided radiotherapy allows daily adaptive replanning and can improve accuracy. Integrating an MRI scanner and linear accelerator (linac) for the MRLinac harnesses the advantages of MRI for intrafractional imaging with the potential for tumour tracking, gated treatment and adaptive radiotherapy. I initially focus on pre-clinical research to model the benefits of the addition of MRI in radiotherapy planning and treatment. I firstly examine prostate motion, as assessed by automatic tracking of fiducials, confirming previously published data on the intrafraction motion of the prostate and setting the scene for the need for adaptive radiotherapy. Further work concentrates on the stages of adaptive treatment and the challenges involved. With more data emerging on the safety and benefits of extreme hypofractionated prostate schedules, I test the feasibility of planning prostate SBRT for the MR-Linac. I assess the factors for online and real-time imaging including the optimisation of MRI sequences and autosegmentation. My final two chapters focus on the clinical MR-Linac workflow. I describe the first-in-man study 'Prostate Radiotherapy Integrated with Simulataneous MRI' (PRISM) trial, treating patients requiring radical prostate radiotherapy on the MR-Linac. There is a complex workflow involved in delivering online adaptive imaging based on the daily anatomy, which has been feasible and in the limited number of patients discussed, not associated with increased toxicity compared to standard treatment. Finally, looking ahead to the changes required to make the workflow more efficient whilst maintaining accuracy, I present data on the accuracy of treatment radiographer and automated propagated contours. This thesis takes each of these steps in turn to assess the feasibility of this novel treatment delivery, which has the potential to optimise fractionation schedules and improve target dose whilst reducing toxicity from treatment.