ABSTRACT
PURPOSE: To describe the rate of gastrointestinal (GI) toxicity after prostate brachytherapy and describe how external beam radiation therapy (EBRT) may influence the association of rectal dose-volume histogram (DVH) parameters with rectal toxicity. METHODS AND MATERIALS: One hundred ten patients with prostate cancer were treated with I-125 brachytherapy alone (n=62, 144 Gy) or as a boost (n=48, 108 Gy) after 45-Gy EBRT. CT-based dosimetry was performed a median of 29 days after implantation. GI toxicity was evaluated by Radiation Therapy Oncology Group criteria. Median followup was 41 months. RESULTS: Eleven patients developed Grade 2+GI toxicity. Men treated with EBRT had an increased risk of GI toxicity, with freedom from Grade 2+ toxicity of 82% vs. 91% for implant alone, but this difference was not statistically significant (p=0.3044). Of the DVH parameters analyzed, only the rectal volume receiving the prescription dose (rV(100)(%)) was associated with late Grade 2+GI toxicity. Men with rV(100%) >or= 0.05 cc had a 4-year freedom from Grade 2+ toxicity of 77% vs. 100% for those with an rV(100%) <0.05 cc (p=0.0248). However, this relationship was only significant for the subset of patients treated with EBRT, where men with rV(100%) >or= 0.05 cc had a 26% risk of Grade 2+ toxicity compared with 0% for rV(100%) <0.05 cc. Additional DVH parameters, including dose to the hottest 0.1 cc (p=0.0199), 1% (p=0.0086), and 3% (p=0.0043), were also associated with GI toxicity but only in men treated with EBRT. CONCLUSIONS: Supplemental EBRT may lower the threshold for rectal toxicity after prostate brachytherapy. Morbidity can be minimized by observing rectal constraints.
