A Randomized Trial on Accelerated Versus Standard Small-margin Radiation Schedule in Patients With Prostate Cancer Treated With Combined Brachytherapy and External Beam Radiation Therapy: Toxicity Outcomes and Patterns of Prostate Movement.

Purpose: Hypofractionated radiation therapy requires high accuracy in dose delivery to enable reduced treatment margins and minimize the dose to organs-at-risk. The purpose of this study was to evaluate whether accelerated (delivered 5 times per week) hypofractionated external beam radiation therapy (EBRT) can be performed without increased acute toxicity using a real-time tracking system. We also aimed to investigate patterns of intrafractional prostate movements. Methods and Materials: Patients with prostate cancer planned for combined high dose rate brachytherapy (14.5 Gy × 1) and EBRT (3 Gy × 14) were included in this randomized trial to receive the EBRT part of the treatment either 3 or 5 times per week. EBRT was delivered using small margins (3 mm) using the Raypilot system for real-time tracking of intrafractional prostate movements. Movements were continuously monitored in 3 dimensions. Primary endpoint was toxicity that was assessed using patient-reported outcome measures through european organisation for research and treatment of cancer (EORTC) quality of life questionnaires QLQ-C30 and QLQ-PR25. Results: During June 2018 to January 2020, 34 patients (median age 70 years) were included in the study of which 17 were randomized to each group. No statistically significant differences in toxicity were found between the study groups. Target displacement was <2 mm during 97.0% of the time and <3 mm during 99.9% of the active treatment time. Conclusions: We found no evidence of increased acute toxicity in patients who received accelerated treatment schedule. Provided that the target is properly delineated, a 3 mm margin seems to be feasible and safe when using a real-time tracking system.