Moderate hypofractionated boost to the prostate with pelvic radiotherapy in high-risk prostate cancer (MOB-RT) - a phase 2 study: acute safety and quality of life outcomes.

Abstract

To evaluate the safety of moderately hypofractionated radiotherapy to the prostate and pelvic elective nodal irradiation (ENI) with intraprostatic and nodal boost in patients with high-risk prostate cancer. In this prospective phase 2 single-arm study, patients with high-risk or node-positive prostate cancer received external beam radiotherapy to the prostate and ENI with moderate hypofractionation (60 Gy in 20 fractions to the prostate; 48 Gy ENI) with ADT. Simultaneous integrated boosts were allowed to 68 Gy to intraprostatic gross disease (MRI-defined) and 55 Gy to radiographically-involved nodes. The primary endpoint was acute gastrointestinal (GI) side effects (CTCAE v5.0) at 3 months following radiotherapy, with an a priori hypothesis that acute grade ≥ 2 GI side effects would not exceed 35%. Secondary endpoints included acute genitourinary (GU) side effects and quality of life (QoL) (EPIC-26 and IPSS). 100 patients were enrolled; 97 completed treatment. Median age was 73, 49% had grade group 4-5 disease, median PSA was 22.2 ng/mL, 21% were cN1. 23 (24%) and 18 (19%) of patients received intraprostatic and nodal boosts, respectively. The rate of acute grade ≥ 2 GI side effects was 15.5% (one-sided 95% upper confidence bound22.8%). On univariable analysis, higher rectal and bowel D1cc and intraprostatic boost were significantly associated with increased acute GI side effects. The rate of grade ≥ 2 acute GU side effects was 26.8% (95% CI 18.3-36.8%). There was no statistically significant detriment to mean GI or GU QoL at 3 months post-treatment. Moderately hypofractionated radiotherapy to the prostate and ENI with boosts to gross disease was associated with lower-than-expected side effects and no statistically significant detriment to patient-reported mean GI or GU QoL at 3 months post-treatment.