Factors predictive of rectal bleeding after 103Pd and supplemental beam radiation for prostate cancer

Purpose To evaluate the contribution of various clinical and radiation treatment parameters to the likelihood of late rectal bleeding after brachytherapy plus supplemental beam radiation (EB). Methods A total of 161 intermediate risk patients, with Gleason score 7 or higher and/or PSA 10–20 ng/ml randomized to implantation with 103Pd (90 versus 115 Gy) with 44 versus 20 Gy EB (2 Gy/day) were studied. Beam radiation was delivered with a four-field arrangement designed to cover the prostate and seminal vesicles with a 2 cm margin (reduced to 1.0 cm posteriorly). Isotope implantation was performed by standard techniques, using a modified peripheral loading pattern. A postimplant CT scan (3 mm slice thickness) was obtained 1–4 h after implantation. Dose volume histograms of the prostate and rectum were calculated using the outer prostatic and rectal margins identified on CT scan by one investigator (KW). Rectal doses were expressed as the R100, R200, and R300, defined as the rectal volume (cc) that received at least 100%, 200%, or 300% of the prescription dose, respectively. External beam doses were expressed as EB75% (cc)—the volume of rectum that received 75% of the beam prescription dose. Treatment-related rectal morbidity was monitored by mailed questionnaires, using Radiation Therapy Oncology Group (RTOG) criteria, at 1, 3, 6, 12, 24, and 36 months. Patients who reported Grade 1 or higher RTOG morbidity were contacted by telephone to obtain more details regarding their rectal bleeding. Results In univariate analysis, rectal bleeding was statistically related to the R100, R200, and R300 values, with p-values of 0.0055, 0.0007, and 0.012, respectively. Bleeding was not related to gap times, prostate size, patient age, V100 or D90 values. The EB75% values were similar in 44 Gy patients with or without late bleeding. Conclusion Considering the potential severity of rectal morbidities and their relationship to implant dose, we urge our colleagues to routinely monitor the rectal implant doses of their own patients to make sure that such doses are kept within an accepted range.