To estimate the rates of rectal bleeding after dose-escalated three-dimensional conformal radiation therapy (3D-CRT) on a prospective, Phase II study in which a modified intrarectal balloon was used for prostate gland localization and immobilization.

The study cohort comprised 100 men with biopsy-proven adenocarcinoma of the prostate and at least one high-risk feature (prostate-specific antigen level greater than 10 ng/mL, Gleason score 7 or higher, or clinical or radiographic T3 disease). Treatment consisted of androgen suppression therapy and four-field 3D-CRT with an intrarectal balloon for the initial 15 treatments. Planning treatment volume dose was 75.6 Gy. The primary endpoint of time to grade 3 rectal bleeding was estimated with the Kaplan-Meier method for 57 men with a minimum follow-up of 1 year.

For 57 men with a median (range) follow-up of 1.8 (1.0 to 3.3) years, the median (range) volume of rectum exceeding 70 Gy was 3.7 (0.6 to 14.7) cm³, and the 2-year estimate of grade 3 rectal bleeding rate was 10%. This rate was 100% as compared with 0 (P <0.0001) for men who were taking warfarin (n = 3) or high-dose aspirin (n = 1) as compared with neither, respectively. All grade 3 rectal bleeding events were controlled with argon plasma coagulation.

Dose-escalated 3D-CRT with an intrarectal balloon technique for prostate localization and immobilization produced no measurable grade 3 rectal bleeding unless the patient was taking anticoagulants.