THE IMPACT OF PATIENT POSITIONING ON RADIATION DOSE TO SMALL BOWEL IN PATIENTS WITH RECTAL CANCER

Purpose: Radiotherapy is a standard neo/adjuvant treatment for rectal cancer, but there is no standard concerning the most optimal treatment position. The aim of this study was to find dose-volume relations in organs at risk (small bowel, total bowel and bladder) for patients treated in prone or supine position. Methods and materials: 91 patients receiving chemoradiotherapy for rectal cancer, mainly preoperatively, were randomized to radiotherapy in prone or supine position. A total dose of 50-54 Gy was given in 25-27 daily fractions of 2 Gy. Small bowel, total bowel and bladder were contured and dose-volume-histograms for these organs were obtained using Oncentra Masterplan v.3.3. treatment planning system. Dose-volume-histograms for small bowel were determined at 5 Gy dose intervals (V5, V10, etc). Descriptive statistics and independent samples T-test were used for analysis. Results: Data from 82 patients were evaluable. No significant differences in doses / dose-volume relations to organs at risk between prone and supine position were identified. However, at low dose-volumes (V5, V10), a larger volume of small bowel was irradiated in the supine position. Conclusion: In this study, radiation treatment of patients with rectal cancer in prone or supine position was equal regarding dose or dose-volume relations to small bowel. The impact of larger low-dose-volume on subjective symptoms should be further investigated.