Stereotactic MR-guided Adaptive Radiation Therapy for Localized Prostate Cancer

Rationale: This prospective study investigates the outcomes of daily online stereotactic MR-guided adaptive radiation therapy (SMART) in patients with localized prostate cancer (cT1c-T3bN0M0). Visualization of the prostate, rectum and bladder prior to and during radiation delivery can be used to deliver "gated" treatment (beam-on only when the prostate is in the predetermined position) using small uncertainty margins. The novel MRIdian treatment delivery system (ViewRay, USA), which will be used for this study, allows for the immediate generation of an optimal radiotherapy plan based on the current anatomy of the prostate and surrounding normal organs prior to each fraction. These major advances will (i.e. dosimetrically) allow for an optimisation of normal tissue radiation doses, which should theoretically decrease toxicity to surrounding organs such as the rectum or bladder. Another advantage of this approach is that online MR-based prostate imaging does not rely on implanted gold markers, avoiding an invasive procedure to insert such markers. If proven feasible, this approach could set a new standard of care for patients with localized prostate cancer. The main goal of this phase II study of SMART for prostate cancer is to evaluate the early and early-delayed toxicity, i.e. within the first year after treatment. An established 5-fraction hypofractionated radiation scheme will be used in this trial. Main outcome parameters will include gastro-intestinal, genitourinary and sexual symptoms, which will be monitored at fixed time points using CTCAE criteria. In addition, patient-reported outcomes will be evaluated using EORTC-QOL questionnaires. Objective: To investigate the early and early-delayed toxicity profile of SMART in patients with localized prostate cancer. Study design:phase II observational study Study population: 100 consecutive patients with localized prostate cancer (cT1c-T3bN0M0). Study intervention: Study patients will be treated with an online M