Efficacy of a belly board device with CT-simulation in reducing small bowel volume within pelvic irradiation fields

Purpose/Objective: Acute and chronic small bowel toxicity associated with pelvic irradiation limits dose escalation for both chemotherapy and radiotherapy for rectal cancer. Various surgical and technical maneuvers including compression and belly board devices (BED) have been used to reduce small bowel volume in treatment fields. However, quantitative dose volume advantages of such methods have not been reported. In this study, the efficacy of BED with CT-simulation is presented with dose-volume histogram (DVH) analyses for rectal cancer. Methods and Materials: Twelve consecutive patients referred to our department with rectal cancer were included in this study. Patients were given oral contrast 1.5 h prior to scanning and instructed not to empty their bladder during the procedure. The initial CT scan,without BED was taken in the prone position with an immobilization cast. A second CT study was performed with a commercially available BED consisting of an 18-cm thick hard sponge with an adjustable opening (maximum 42 x 42 cm(2)). All patients were positioned prone over the BED so that the opening was above the treatment volume and usually extended from the diaphragm to the bottom of the fourth lumbar spine. Image fusion between both sets of CT scans (with and without BED) was performed using common bony landmarks to maintain the same target volume. The critical structures including small bowel and bladder were delineated on each slice for DVH analysis. On each study, a three-field optimized plan with conformal blocks in beams-eye-view was generated for volumetric analysis. The DVHs with and without BED were evaluated for each patient. Results: The median age and body weight of 12 patients (4 females and 8 males) were 57.5 years and 82.7 kg, respectively. The changes in posterior-anterior (PA) and lateral separation with and,without BED at central axis slices were analyzed. The changes in lateral separation were minimal (<0.8 cm); however, the PA separation was reduced by 11.3 +/- 3.3% when BED was used. The reduction in PA separation was directly related to the reduction in small bowel volume. The small bowel volume was significantly reduced with a median reduction of 70% (range 10-100%) compared to the small bowel volume without BED. The small bowel volume reduction did not correlate either with body weight, age, gender, or sequence of radiation treatment,vith surgery (pre-op vs. post-op). The DVH analysis of small bowel with BED showed significant volume reduction at each dose level. For 50% patients, the DVH analysis demonstrated an increase in bladder volume with BED. All patients treated with the BED completed their treatment without any break and without significant acute gastrointestinal or genitourinary toxicity. Conclusions: For rectal cancers, small bowel is the dose-limiting structure for acute and chronic toxicity. The use of the BED should improve the tolerance of aggressive combined modality treatment by reducing the small bowel volume within the pelvis compared to the prone position alone. The BED provides an easy, economical, comfortable, and noninvasive technique to displace small bowel from pelvic treatment fields. The small bowel volume is dramatically reduced at each dose level. The volume reduction does not correlate with gender, age, weight, pelvic separation, and sequence of radiation treatment vs. surgery. (C) 1997 Elsevier Science Inc.