Background: We aimed to evaluate patient-reported functional outcomes (PRO) following definitive radiation therapy (RT) for prostate cancer (PCa) in a real-life population-based setting. Methods: The population-based Victorian Prostate Cancer Outcomes Registry (PCOR-Vic) captures approximately 90% of all PCa cases in the state. From 2015 onwards, all men in PCOR-Vic were contacted to complete the Expanded Prostate Cancer Index Composite short-form 26 (EPIC-26) at 12-month post-treatment. The EPIC-26 included urinary incontinence, urinary obstructive, bowel, sexual and hormonal function domain scores, ranging from 0 to 100, with higher score representing better outcomes. We estimated differences in the EPIC-26 domain scores between different RT techniques using linear regression, adjusting for patient, tumor, and treatment related factors, including the use of androgen deprivation therapy (ADT). The nature of recruitment methods and data collection in PCOR-Vic precluded us from measuring EPIC-26 prior to treatment, and hence this was not adjusted for in our analyses. Results: Between 2015 and 2020, there were 1,898 men treated with definitive RT who completed the EPIC-26 questionnaires and were included in this study – 1551 (82%) had external beam radiation therapy (EBRT) alone, 91 (5%) had EBRT with brachytherapy boost (EBRT+BT), 204 (11%) had low-dose-rate brachytherapy (LDR-BT) alone, and 52 (3%) had high-dose-rate brachytherapy (HDR-BT) alone. There were 1,140 (60%) men who had ADT with RT – 68% with EBRT alone, 76% with EBRT+BT, 4% with LDR-BT, and 21% with HDR-BT (P < 0.001). Compared to men who had EBRT alone, men who had LDR-BT had higher adjusted mean EPIC-26 urinary incontinence (8.6 points; 95%CI: 5.3-12.0; P < 0.001), sexual (13.5 points; 95%CI: 9.2-17.8; P < 0.001) and hormonal score (6.8 points; 95%CI: 3.5-10.1; P < 0.001) at 12-month post-treatment. Compared to men who had EBRT alone, there were no statistically significant differences in all five EPIC-26 domain scores in men who had EBRT+BT or HDR-BT alone. Conclusions: This is the first Australian real-world evidence on PRO for different RT modalities for PCa on a population-based level. We observed better urinary incontinence, sexual and hormonal function in men who had LDR-BT compared to EBRT, but no significant differences between men who had EBRT, EBRT+BT or HDR-BT.