TOWARDS MRI-GUIDED GANTRY-FREE RADIATION THERAPY: QUANTIFYING DEFORMATION AND PATIENT TOLERANCE

Delivery of external beam radiation therapy usually requires relative rotation between the radiation source and the patient. Typically this is achieved by rotating the radiation around the patient using a gantry. An alternative approach is to instead rotate a patient relative to a stationary radiation source i.e. gantry-free radiotherapy. Removing the requirement of a rotating gantry would reduce the costs and space requirements for proton and heavy ion facilities, enable cheaper x-ray systems, facilitate synchrotron-based x-ray treatments and offer a much more practical approach for integrating MRI with proton treatments in the future. In this thesis, four studies were performed to address key barriers to gantry-free RT. Anatomical changes caused by rotation need to be considered for gantry-free treat- ments. In chapter 3, global pelvic rigid and non-rigid deformation was quantified for a cohort of 8 healthy participants rotated 360 degrees in 45-degree increments within a radiotherapy dedicated MRI scanner. Rigid translations of the participants between 5.8 – 30.0 mm were observed, which were most substantial in the left-right direction. Maximum displacement occurred at the 90 and 270 degree couch angles. Non-rigid deformation was greatest around the external body surface, up to 28.0 mm in mag- nitude for some participants. Internal prostate, rectum and bladder motion was then compared to the supine position for a cohort of 9 prostate cancer patients in chapter 4. Organ motion was largest at the 180-degree (prone) couch position. Prostate motion was < 2 mm in the left-right direction, 0 – 14 mm in the superior-inferior direction and -11 – 4 mm in the anterior-posterior direction.