Part I | Chapter 6 110 Abstract Background Magnetic resonance imaging (MRI)-guided radiotherapy is a new technique for treatment of localised prostate cancer. We report the 12-month outcomes for the first prostate cancer patients treated within an international consortium (MOMENTUM study) on a 1.5 T MR-Linac system with ultra-hypofractionated radiotherapy. Materials and methods Patients treated with 5 x 7.25 Gy were identified. Prostate-specific antigen (PSA) level, physicianreported toxicity (Common Terminology Criteria for Adverse Events [CTCAE]), and patient-reported outcomes (PRO) (QLQ-PR25 and QLQ-C30 questionnaires) were recorded at baseline and at 3, 6, and 12 months of follow-up (FU). Pairwise comparative statistics were conducted to compare outcomes between baseline and FU. Results Four-hundred-and-twenty-five patients with localised prostate cancer (11.4% low-, 82.0% intermediate-, and 6.6% high-risk) were included, and 365, 313, and 186 patients reached 3, 6, and 12 months FU, respectively. Median PSA level declined significantly to 1.2 ng/mL and 0.1 ng/mL at 12 months FU for the non-ADT and ADT group, respectively. The peak of genitourinary and gastrointestinal CTCAE toxicity was reported at 3 months FU, with 18.7% and 1.7% grade ³ 2, respectively. The QLQ-PR25 questionnaire outcomes showed significant deterioration in urinary domain score at all FU moments. For the non-ADT group, physician- and patient-reported erectile function worsened significantly between baseline and 12 months FU. Conclusion Ultra-hypofractionated MRI-guided radiotherapy for localised prostate cancer using a 1.5 T MR-Linac is effective and safe. The peak of CTCAE genitourinary and gastrointestinal toxicity was reported at 3 months FU. Furthermore, a significant increase in CTCAE erectile dysfunction was reported at 12 months FU. These data are useful for educating patients on expected outcomes and informing study design of future comparative-effectiveness studies.
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