The Headline: In the largest prospective comparison to date, proton therapy failed to demonstrate superior outcomes with prostate radiation.
The Study: Proton proponents have long pointed to dosimetric advantages as a pathway to fewer GI side effects, but early results from the prospective COMPPARE study suggest those benefits may not translate into measurable patient outcomes. This pragmatic, non-randomized comparison enrolled over 2,500 men with localized prostate cancer treated at 51 centers, including 1,404 receiving proton therapy and 939 receiving IMRT. After inverse probability weighting and a median follow-up of 4 years, the primary endpoint of patient-reported bowel urgency and frequency demonstrated no clear difference at any measured timepoint in the first 2 years. Likewise, rates of grade 2+ GI events were nearly identical (5.2% with protons vs 5.6% with IMRT. Disease control was also superimposable, with 3-year freedom from biochemical progression of 98.0% versus 97.9%. Notably, the study allowed contemporary treatment approaches including moderate hypofractionation, rectal spacers, and physician-directed ADT use, meaning this should be broadly applicable to current practice.
TBL: This larger real-world cohort mirrored outcomes from the randomized PARTIQoL trial where an incremental benefit with proton therapy has not proved demonstrable given excellent outcomes reported with modern IMRT for prostate radiation. | Mendenhall, ASCO 2026
The Study: Proton proponents have long pointed to dosimetric advantages as a pathway to fewer GI side effects, but early results from the prospective COMPPARE study suggest those benefits may not translate into measurable patient outcomes. This pragmatic, non-randomized comparison enrolled over 2,500 men with localized prostate cancer treated at 51 centers, including 1,404 receiving proton therapy and 939 receiving IMRT. After inverse probability weighting and a median follow-up of 4 years, the primary endpoint of patient-reported bowel urgency and frequency demonstrated no clear difference at any measured timepoint in the first 2 years. Likewise, rates of grade 2+ GI events were nearly identical (5.2% with protons vs 5.6% with IMRT. Disease control was also superimposable, with 3-year freedom from biochemical progression of 98.0% versus 97.9%. Notably, the study allowed contemporary treatment approaches including moderate hypofractionation, rectal spacers, and physician-directed ADT use, meaning this should be broadly applicable to current practice.
TBL: This larger real-world cohort mirrored outcomes from the randomized PARTIQoL trial where an incremental benefit with proton therapy has not proved demonstrable given excellent outcomes reported with modern IMRT for prostate radiation. | Mendenhall, ASCO 2026