Prostate bed irradiation with alternative radio-oncological approaches (PAROS) - a prospective, multicenter and randomized phase III trial.

Background: For patients with treatment-naïve carcinoma of the prostate, hypofractionated irradiation becomes more and more popular. Due to the low α/β value of prostate cancer, increased single dose leading to a shortened treatment period seems to be safe and feasible. However, reliable data is lacking for post-prostatectomy patients so far. Further, the role of proton therapy is still under debate. Two prospective phase II trials with both, hypofractionated photon and proton therapy, provided promising results.

Methods/ Design: The PAROS trial is a prospective, multicenter and randomized phase III trial for men with localized prostate carcinoma after surgery. Post-prostatectomy patients will be randomized to either normofractionated radiotherapy (nRT) with photons (70.0/ 2.0 Gy), or hypofractionated radiotherapy (hRT) with photons (57.0/ 3.0 Gy) or hRT with protons (57.0/ 3.0 Gy relative biological effectiveness [RBE]). Block randomization is stratified by Gleason Score (≤ 7 vs. > 7) and treatment indication (adjuvant vs. salvage). The trial is planned to enroll 897 patients. The primary objective is to show an improvement in the bowel-score according to EORTC QLQ-PR25 after proton therapy compared to photon irradiation (week 12 vs. baseline). Secondary aims are non-inferiority of hRT compared to nRT with regard to biochemical progression-free survival (bPFS), overall survival (OS), quality of life and toxicity.

Discussion: The present study aims to evaluate the role of hypofractionated radiotherapy to the prostate bed with photons and protons leading to significant impact on future management of operated men with prostate cancer.

Trial Registration: Deutsches Register klinischer Studien: DRKS00015231 ; registered 27 September 2018.