Salvage radiation therapy in prostate cancer: relationship between rectal dose and long-term, self-reported rectal bleeding

PURPOSE: To quantify the relationship between the rectal dose distribution and the prevalence of self-reported rectal bleeding among men treated with salvage radiotherapy (ST) delivered by three-dimensional conformal radiotherapy (3DCRT) for prostate cancer. To use this relationship to estimate the risk of rectal bleeding for a contemporary cohort of patients treated with volumetric modulated arc therapy (VMAT) ST. METHODS AND PATIENTS: Rectal bleeding of any grade was reported by 56 (22%) of 255 men in a PROM-survey at a median follow-up of 6.7 years after 3DCRT ST. Treatment plan data were extracted and dose–response relationships for the rectal volumes receiving at least 35 Gy (V(35Gy)) or 63 Gy (V(63Gy)) were calculated with logistic regression. These relationships were used to estimate the risk of rectal bleeding for a cohort of 253 patients treated with VMAT ST. RESULTS: In the dose–response analysis of patients in the 3DCRT ST cohort, both rectal V(35Gy) and V(63Gy) were statistically significant parameters in univariable analysis (p = 0.005 and 0.003, respectively). For the dose–response models using either rectal V(35Gy) or V(63Gy), the average calculated risk of rectal bleeding was 14% among men treated with VMAT ST compared to a reported prevalence of 22% for men treated with 3DCRT ST. CONCLUSIONS: We identified dose–response relationships between the rectal dose distribution and the risk of self-reported rectal bleeding of any grade in a long-term perspective for men treated with 3DCRT ST. Furthermore, VMAT ST may have the potential to decrease the prevalence of late rectal bleeding.