A simple technique to reduce small bowel toxicity when irradiating the periaortic area

Purpose/Objective: Patients receiving periaortic radiation are normally treated in the supine position. We decided to evaluate whether positioning the patient prone on a modified 'belly-board' can reduce the volume of small bowel within the lateral fields in patients receiving four field periaortic radiation. Materials and Methods: Sixteen consecutive women with gynecologic primaries underwent simulation of the periaortic area using a four-field set up (AP, PA, Lats). The fields extended from the top of the L1 vertebral body to the bottom of L5 and had a mean length of 16.2 cm. The AP and PA fields had a width of 8 cm (centered on the midline of the vertebral bodies) while the right and left lateral fields had a width of 4 cm (2 cm anterior and 2 cm posterior to the anterior margin of the vertebral bodies) and did not include the spinal cord. Following oral ingestion of small bowel contrast, simulation films were obtained in the supine position and in the prone position on a modified 'belly-board' (with the pelvic opening extended superiorly to the superior abdomen). It was hypothesized that the prone position on a modified 'belly-board' would allow the abdominal small bowel to fall by gravity away from the periaortic area. We measured the volume of small bowel irradiated through the lateral fields for both the supine and prone-in-belly-board positions using the method described by Gallagher et al. Results: The volume of small bowel included within the lateral fields in the supine position ranged from 164 to 359.5 cc3 (mean 285 cc3) while placement in the prone-in-bellyboard position reduced the volume of small bowel within the lateral fields to a range of 35-152 cc3 (mean 86 cc3), an overall reduction of approximately 70% in the volume of small bowel included within lateral fields. Conclusion: The use of lateral fields in the prone-in-bellyboard position allows for significant small bowel sparing through the lateral component of a four-field periaortic set-up. Since approximately 1500 c9y (as to not exceed kidney tolerance) can be delivered through the lateral fields, this dose can be important considering the minimal dose difference between control of microscopic disease and small bowel damage. This technique can improve the therapeutic ratio in patients receiving periaortic radiotherapy primarily or prophylactically