Population-level trends in radiation treatment of low-risk prostate cancer.

336 Background: Reducing overtreatment of localized prostate cancer remains a public health goal, particularly for patients with low-risk disease who are candidates for active surveillance. We evaluated population-level trends in disease risk among patients treated with radiation therapy for localized prostate cancer over the past fifteen years. Methods: Men with localized prostate cancer (N0M0) treated with external beam radiation or brachytherapy were identified from three distinct cohorts: the Surveillance, Epidemiology, and End Results (SEER) U.S. population registry (2010–2022, n=156,149); the Veterans Affairs (VA) integrated national health system (2010–2024, n=34,635); and the Michigan Radiation Oncology Quality Consortium (MROQC) statewide quality collaborative (2021–2025, n=2,348). The primary outcome was the proportion of radiation-treated patients classified as low-risk per guidelines (T1-2a, Grade Group 1, PSA <10 ng/mL) compared to those treated with intermediate- or high-risk disease. Patients receiving radiation more than one year after diagnosis were excluded to account for disease progression on active surveillance. Logistic regression adjusted for baseline covariates. Secondary analyses compared proportions across cohorts in overlapping years (2021–2022) using pairwise two-proportion z-tests. Results: The proportion of radiation-treated patients with low-risk disease declined from 33.7% to 7.6% (2010-2022) in SEER and from 22.9% to 2.0% (2010-2024) in the VA. Rates remained low in MROQC (2.8% to 4.2%, 2021-2025). In all cohorts, older age was associated with lower rates of radiation for low-risk disease (adjusted odds ratios [AOR] per 5 years: 0.70, 0.70, and 0.77; 95% CI: 0.70-0.71, 0.68-0.72, and 0.68-0.89, all p<0.001, in SEER, VA, MROQC respectively). Declines over time were statistically significant in SEER and the VA (AOR per 5 years: 0.46 and 0.44; 95% CI: 0.45-0.47 and 0.41-0.46, both p<0.001). In 2021 and 2022, the proportion of low-risk cases was lower in the VA and MROQC than in SEER (both p<0.01). Conclusions: Among men receiving radiation for localized prostate cancer, the proportion with low-risk disease has declined by more than 75% since 2010. Across all three cohorts (SEER, VA, MROQC), only 2-8% of patients treated with contemporary radiation therapy had low risk disease. This pattern parallels surgical trends and reflects improved diagnostic pathways and broader adoption of active surveillance for low-risk disease.