Impact on rectal dose from the use of a prostate immobilization and rectal localization device for patients receiving dose escalated 3D conformal radiation therapy.

PURPOSE When >25% of the rectum is irradiated to > or = 70 Gy, the risk of developing Grade 2 or higher rectal complications is significantly increased. This study evaluates the impact on dose to the rectum from the use of an intrarectal (IR) balloon device, previously shown to immobilize the prostate gland and localize the rectum, in patients receiving dose escalated 3-dimentional (3D) conformal radiation therapy. MATERIALS AND METHODS From July 2001 through February 2003, 28 consecutive patients with prostate cancer underwent computerized tomography-based simulation with and without the IR balloon in place. Treatment planning was performed for three clinical paradigms in which the IR balloon was not used at all (0 Gy), used during the cone-down for 15 treatments (28.35 Gy), or used for the entire course of 40 treatments (75.6 Gy). The three plans were compared for differences in the percent of rectum receiving >70 Gy. RESULTS Dose volume histogram (DVH) analysis revealed that the median(range) of percent rectal volume exceeding 70 Gy was 25% (12.7-41.5%), 7.5% (0.9-19.5%), and 3.6% (0-8.7%) for patients in whom the IR balloon was used for 0, 15, and 40 treatments, respectively. The percent of rectum exceeding 70 Gy was significantly different for all treatment plan comparisons (P < 0.0001). CONCLUSIONS Grade 2 or higher rectal toxicity may be minimized during dose escalated 3D conformal radiation therapy through the use of an IR balloon during the 3-week cone down portion of an 8-week treatment course.