Rectal morbidity following I-125 prostate brachytherapy in relation to dosimetry

Background: To investigate rectal morbidity after I-125 prostate brachytherapy and to analyze predictive factors of rectal morbidity. Methods: A group of 227 consecutive patients with localized prostate cancer were treated with I-125 prostate brachytherapy with or without external beam radiotherapy (EBRT) between September 2003 and January 2005. Rectal morbidity (diarrhea, bleeding and pain) was evaluated using the Radiation Therapy Oncology Group (RTOG) criteria. Dosimetry was based on computerized tomography (CT) scan 1 month post-implant. The clinical, treatmentrelated and dosimetric factors were evaluated for the risk of grade 2 rectal morbidity. Rectal dosimetric factors included the rectal volume that received. 100% and 150% of the prescribed dose, and the maximal rectal dose which was defined as the sum of the minimal dose received by 1% of the rectum volume and the prescribed dose of EBRT. Results: Grade 2 rectal bleeding occurred in 10 (4.4%): for nine patients within the first year and for one patient between the first and second year. Grade 2 diarrhea occurred in one patient (0.4%) within the first year. No patient reported grade 2 pain. In the univariate analysis with grade 2 rectal bleeding, there were significant correlations with number of seeds, supplemental EBRT, and all of the rectal dosimetric parameters. On subsequent multivariate analysis, the only significant factor was the maximal rectal dose (P < 0.001). Rectal dose > 160 Gy was correlated to grade 2 rectal morbidity. All the patients with rectal dose > 160 Gy received EBRT. Conclusions: Manifestations of rectal morbidity are acceptable events after I-125 prostate brachytherapy. Rectal dose-volume histogram for the brachytherapy is a predictive method for assessing the risk of developing grade 2 rectal bleeding. Delivery of the rectal dose should not exceed 160 Gy in order to avoid rectal complications.