Rectal function following brachytherapy with or without supplemental external beam radiation: Results of two prospective randomized trials

Purpose To evaluate the effect of isotope and supplemental external beam radiation therapy (XRT) on brachytherapy-related rectal morbidity, using prospective, patient-administered quality of life (QOL) assessments. Methods and materials Two hundred thirteen consecutive patients (median follow-up 22 months) were implanted on 2 prospective randomized brachytherapy trials evaluating the effect of isotope for low-risk patients and different doses of supplemental XRT for patients with higher risk features. Treatment-related rectal morbidity was evaluated by modified Radiation Therapy Oncology Group (RTOG) criteria and the multifactorial Rectal Function Assessment Score (R-FAS). Clinical, treatment and dosimetric parameters evaluated included patient age, diabetes, hypertension, tobacco consumption, clinical stage, prostate ultrasound volume, elapsed time since implant, hormonal manipulation, supplemental XRT, isotope, treatment planning volume, and values of the minimum dose received by 90% of the prostate gland (D90), the percent prostate volume receiving 100%, 150%, and 200% of the minimum peripheral dose (V100/150/200), rectal implant doses (V75/100/125/150 and D5/10/25/50) and rectal XRT doses (D5/10/25/50/75). Results Using the RTOG instrument, rectal morbidity peaked at 1 month. The pre- and most recent postimplant median RTOG scores were 0 and 0, respectively. The pre- and postimplant R-FAS scores were 2.41 and 3.83, respectively. With time, the rectal scores for both instruments improved and approached baseline. In multivariate analysis, only the rectal dosimetry variable D5 predicted for bowel function when using the R-FAS instrument. No clinical, treatment, or dosimetric parameters predicted for bowel function when using the RTOG survey. No patient required surgical intervention for rectal complications. Conclusions The multifactorial R-FAS elucidated fine gradations in bowel function of a severity less than RTOG Grade 3 morbidity. Of multiple clinical, treatment, and dosimetric parameters evaluated, only the minimum dose received by 5% of the rectum (D5) correlated with rectal dysfunction via the R-FAS instrument, while none of the evaluated parameters predicted for bowel dysfunction using the RTOG survey. Following permanent prostate brachytherapy, the ability to discern subtle changes in rectal function is dependent on the sensitivity of the survey instrument