Phase 2 study of moderately hypofractionated prostate boost with pelvic RT for high-risk prostate cancer: acute safety and QOL outcomes

The multicenter phase 2 MOB-RT trial in Canada evaluated the safety of moderately hypofractionated radiotherapy (RT) to the prostated and pelvic elective nodal irradiation (ENI) with intraprostatic and nodal boost in patients with high-risk prostate cancer. Patients received EBRT to the prostate (60 Gy in 20 fractions) and ENI (48 Gy) with androgen deprivation therapy. 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 at 3 months following RT, 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). Among 100 patients enrolled (median age 73 years; 49% grade group 4-5 disease;median PSA 22.2 ng/ml; 21% cN1), 97 completed treatment. Twenty-three and 18 patients received intraprostatic and nodal boosts, respectively. The rate of acute grade ≥ 2 GI side effects was 15.5% (95% upper confidence bound 22.8%). 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. The authors conclude that moderately hypofractionated RT to the prostate and ENI with boosts to gross disease was associated with lower-than-expected side effects and no detriment to GI or GU QOL at 3 months.