Simple SummaryWe looked at the long-term quality of life of patients treated with modern radiotherapy for relapsed prostate cancer after initial surgery. By comparing the original radiotherapy treatment plans with the reported quality of life of the patients, we looked for correlations between the doses received by the healthy pelvic organs and patients’ long-term quality of life. In contemporary radiotherapy practice, healthy organs are spared as much as possible from the high doses required to treat the cancer in order to avoid side effects. We were able to show that patient’s quality of life may also be impacted by low doses to their pelvic organs. Therefore, it seems desirable that specific thresholds need to be established in the low dose spectrum as well in order to further improve patients’ quality of life after radiotherapy. Since this is a complex endeavor requiring extensive research, we provide future researchers with our entire dataset in order to hopefully facilitate their work.AbstractIntroduction: Prostate bed radiotherapy (RT) is a major affecter of patients’ long-term quality of life (QoL). To ensure the best possible outcome of these patients, dose constraints are key for optimal RT planning and delivery. However, establishing refined dose constraints requires access to patient-level data. Therefore, we aimed to provide such data on the relationship between OAR and gastrointestinal (GI) as well as genitourinary (GU) QoL outcomes of a homogenous patient cohort who received dose-intensified post-operative RT to the prostate bed. Furthermore, we aimed to conduct an exploratory analysis of the resulting data. Methods: Patients who were treated with prostate bed RT between 2010 and 2020 were inquired about their QoL based on the Expanded Prostate Cancer Index Composite (EPIC). Those (n = 99) who received volumetric arc therapy (VMAT) of at least 70 Gy to the prostate bed were included. Dose-volume histogram (DVH) parameters were gathered and correlated with the EPIC scores. Results: The median age at the time of prostate bed RT was 68.9 years, and patients were inquired about their QoL in the median 2.3 years after RT. The median pre-RT prostate-specific antigen (PSA) serum level was 0.35 ng/mL. The median duration between surgery and RT was 1.5 years. The median prescribed dose to the prostate bed was 72 Gy. A total of 61.6% received prostate bed RT only. For the bladder, the highest level of statistical correlation (p< 0.01) was seen for V10-20Gy, Dmean and Dmedian with urinary QoL. For bladder wall, the highest level of statistically significant correlation (p< 0.01) was seen for V5-25Gy, Dmean and Dmedian with urinary QoL. Penile bulb V70Gy was statistically significantly correlated with sexual QoL (p< 0.05). A larger rectal volume was significantly correlated with improved bowel QoL (p< 0.05). Sigmoid and urethral DVH parameters as well as the surgical approach were not statistically significantly correlated with QoL. Conclusion: Specific dose constraints for bladder volumes receiving low doses seem desirable for the further optimization of prostate bed RT. This may be particularly relevant in the context of the aspiration of establishing focal RT of prostate cancer and its local recurrences. Our comprehensive dataset may aid future researchers in achieving these goals.