Contemporary post-prostatectomy radiation therapy for prostate cancer within a statewide quality consortium.

369 Background: The 2024 AUA Salvage Therapy for Prostate Cancer Guideline provides guidance at the time of suspected recurrence after radical prostatectomy (RP). Recommendations include early initiation of post-operative radiation therapy (RT), and the addition of androgen deprivation therapy (ADT) for those with high-risk features. Given that an increasing number of men receive RP for high-risk disease, we characterized RT in a prospective cohort from the Michigan Radiation Oncology Quality Consortium (MROQC) and the Michigan Urological Surgery Improvement Collaborative (MUSIC). Methods: Patients who received post-RP RT at an MROQC center from 06/09/20 – 09/18/24 were eligible. The MUSIC database provided surgical pathology variables, and MROQC prospectively collected data via patient-, physician-, and physicist-completed forms. RT was defined as adjuvant (pre-RT PSA <0.1 ng/mL), consolidative (persistently elevated PSA post-RP), or salvage. Multivariable analyses (MVA) were used to evaluate associations between ADT intent and patient and clinical features, including high risk features (pT3b/T4, pN1, grade group (GG) 4/5, pre-RT PSA >0.5 ng/mL, consolidative). Results: A total of345 patients at 26 centers received RT. The median pre-RT PSA was 0.3 ng/mL (IQR: 0.2-0.6); PET staging was done in 60%, and 34% had genomics testing. RT was adjuvant in 10% (n = 35), consolidative in 28% (n = 95), and salvage in 62% (n = 215). Median pre-RT PSA in each subgroup was 0.07 (IQR: 0.03-0.09), 0.5 (IQR: 0.3-1.5), and 0.3 (IQR: 0.2-0.5) ng/mL, respectively (p=0.005). Median time to RT post-RP was 8, 6, and 29 months, respectively. Most patients (62%) had at least one high risk feature including pT3b (24%), pN1 (5%), GG 4/5 (30%), Pre-RT PSA >0.5 ng/mL (27%), and PSA persistence (28%). Consolidative patients had worse pathologic features compared to salvage patients: pT3b (35% vs. 15%), pN1 (9.5% vs. 0.5%), GG 4/5 (42% vs. 24%), and pre-RT PSA (0.5 vs. 0.3 ng/mL), p<0.01 for all. Sixty percent (n = 204) were prescribed ADT, with an intended duration of ≤6 months in 133 men (65%) and ≥24 months in 34 (17%). On MVA, ADT use was positively associated with high-risk features including pN1 (OR 6.22 [95% CI 1.35 – 47.57]), pT3b/T4 (ref. pT2, OR 2.77 [95% CI 1.34 – 5.93]), GG 4/5 (ref. GG 1/2, OR 2.87 [95% CI 1.51 – 5.56]), pre-RT PSA ≥0.5 ng/mL (OR 2.11 (95% CI 1.17 – 3.91]). ADT was less often used with adjuvant RT (ref. salvage, OR 0.17 [95% CI 0.06 – 0.45]). Conclusions: In a contemporary statewide quality consortium, salvage RT was delivered at a PSA ≤0.5 in nearly 75% of patients, and ADT use was associated with high-risk features. Importantly, 62% of patients have at least one high-risk feature, and over 25% received consolidative RT for persistently positive PSA. Optimized treatment strategies are needed for this at-risk population that has been underrepresented on many modern trials.