Incidence and dosimetric predictive factors of late rectal toxicity after low-dose-rate brachytherapy combined with volumetric modulated arc therapy in high-risk prostate cancer at a single institution: Retrospective study.

Abstract Purpose The purpose of this study is to investigate the incidence of rectal toxicity and to identify the associated dosimetric predictive parameters after I-125 seed low-dose-rate brachytherapy (LDR-BT) combined with volumetric modulated arc therapy (VMAT) and dose constraints. Methods and Materials In total, 110 patients with high-risk prostate cancer received 110 Gy LDR-BT, followed by 45 Gy VMAT. Rectal toxicity was recorded according to Common Terminology Criteria for Adverse Events v.4.03. The dosimetric factors associated with LDR-BT and VMAT were analyzed to determine their relationship with rectal toxicity. Receiver operating characteristic (ROC) curve analysis was performed for ≥ grade 2 (G2) rectal toxicity prediction. Results The follow-up duration was 10.1–115.2 months (median 60.5 months). Seven patients had G2 rectal hemorrhage, and none of the patients had grade 3 rectal hemorrhage. In the univariate analysis, the rectal volume receiving 100% of the prescribed dose (rV100) (p  Conclusion Predictors of late ≥ G2 rectal hemorrhage are rV100, rD2cc, and combined rD2cc. The incidence of rectal toxicity is low and acceptable in this setting and is highly dependent on the rectal dose of LDR-BT. The use of higher-quality LDR-BT and VMAT dose constraints may further reduce the rate of rectal hemorrhage.