Background: Although radiotherapy (RT) technique, patient age and comorbidity are predictive of late RT toxicity, we postulated that there could be an association of the most responsible treating physician (MRP) with treatment-related morbidities. To test this hypothesis, we performed a secondary analysis of a phase III randomized controlled study exploring the optimal sequencing of androgen deprivation therapy (ADT) with dose-escalated prostate RT (PRT) in men with localized prostate cancer (LPCa).Patients and Methods: Men with newly diagnosed LPCa with Gleason score (GS) ≤7, stage T1b-T3a, and PSA <30 were randomized to receive ADT for 6 months (mos) starting 4 mos prior to RT (NAHT arm) or simultaneously with RT (CAHT arm). Toxicity assessments were done weekly during PRT, monthly during ADT, 1 mo after RT, q4 mos in the first year, q6 mos for the next 4 years, and annually thereafter. For late RT-related gastrointestinal (GI) and genitourinary (GU) toxicity, overall (cumulative) toxicity scores were taken as the highest of the 2 scores. The earliest date from either source on which a toxicity grade (Gr) of ≥3 was reported was defined as the date of incidence of Gr ≥3 late toxicity. Incidence probabilities of Gr ≥3 late toxicities were estimated by the Kaplan-Meier method. Cox multivariable regression with maximum likelihood ratio was applied with age, treatment arm, baseline comorbidity, baseline PSA, clinical T stage and GS as fixed effects. As random effects, we had intercepts for subjects and MRPs. Results: A total of 432 patients were randomized to either NAHT (n=215) or CAHT (n=217) arm, respectively. 3-year cumulative incidence of late RT-related Gr ≥3 GI, GU or any-type toxicity in NAHT arm was 2.5%, 2.9% and 4.8% while in CAHT arm was 3.9%, 2.9% and 6.2%, respectively, with no significant difference on log-rank test. On Cox regression, we found that MRP had a significant effect on incidence of Gr ≥3 any-type toxicity (relative risk: 1.36; p=0.047). There was some association of MRP with incidence of Gr ≥3 GI toxicity (relative risk: 2.13; p=0.14), but not with GU toxicity (p=0.45). Conclusions: The current study shows a significant association of MRP with late RT-related Gr ≥3 any-type and a modest evidence of association with late RT-related Gr ≥3 GI toxicity. The findings allude to the importance of peer review in quality assurance of radiotherapy treatment in patients of LPCa.