COMPPARE Proton Therapy vs IMRT (photon) Shows No 2-Year Bowel QOL Advantage in Localized Prostate Cancer

COMPPARE (NCT03561220) is a large prospective, non-randomized comparative effectiveness study testing proton therapy (PT; particle RT with Bragg-peak dose deposition) versus photon IMRT in treatment-naïve localized prostate cancer (excluding very high-risk), allowing conventional and moderately hypofractionated schedules and discretionary ADT/rectal spacers across 51 sites (analyzed PT n=1,404; IMRT n=939; median follow-up 4.0 years). The 2-year primary endpoint showed no difference in EPIC bowel urgency (p=0.324) or bowel frequency (p=0.514) trajectories with inverse probability of treatment weighting; clinician-reported 2-year CTCAE v5 grade ≥2 GI toxicity was similarly low (5.2% PT vs 5.6% IMRT; HR 0.91, 95% CI 0.65–1.28; p=0.6). Exploratory 3-year freedom from biochemical progression was essentially identical (98.0% PT vs 97.9% IMRT; HR 0.95, 95% CI 0.52–1.71; p=0.90), landing squarely in the high tumor-control range expected with contemporary definitive external-beam RT for favorable/intermediate-risk populations.