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

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.

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.

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.

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.