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 w ith pelvic irradiation limits dose escalation for both chemotherapy an d radiotherapy for rectal cancer. Various surgical and technical maneu vers including compression and belly board devices (BED) have been use d to reduce small bowel volume in treatment fields. However, quantitat ive dose volume advantages of such methods have not been reported. In this study, the efficacy of BED with CT-simulation is presented with d ose-volume histogram (DVH) analyses for rectal cancer. Methods and Mat erials: Twelve consecutive patients referred to our department with re ctal cancer were included in this study. Patients were given oral cont rast 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 th e prone position with an immobilization cast. A second CT study was pe rformed with a commercially available BED consisting of an 18-cm thick hard sponge with an adjustable opening (maximum 42 x 42 cm(2)). All p atients were positioned prone over the BED so that the opening was abo ve 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 landma rks to maintain the same target volume. The critical structures includ ing small bowel and bladder were delineated on each slice for DVH anal ysis. On each study, a three-field optimized plan with conformal block s in beams-eye-view was generated for volumetric analysis. The DVHs wi th and without BED were evaluated for each patient. Results: The media n 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 (P A) 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 wa s used. The reduction in PA separation was directly related to the red uction in small bowel volume. The small bowel volume was significantly reduced with a median reduction of 70% (range 10-100%) compared to th e small bowel volume without BED. The small bowel volume reduction did not correlate either with body weight, age, gender, or sequence of ra diation treatment,vith surgery (pre-op vs. post-op). The DVH analysis of small bowel with BED showed significant volume reduction at each do se level. For 50% patients, the DVH analysis demonstrated an increase in bladder volume with BED. All patients treated with the BED complete d their treatment without any break and without significant acute gast rointestinal or genitourinary toxicity. Conclusions: For rectal cancer s, small bowel is the dose-limiting structure for acute and chronic to xicity. 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 e asy, economical, comfortable, and noninvasive technique to displace sm all bowel from pelvic treatment fields. The small bowel volume is dram atically reduced at each dose level. The volume reduction does not cor relate with gender, age, weight, pelvic separation, and sequence of ra diation treatment vs. surgery. (C) 1997 Elsevier Science Inc.