Supine vs Prone Positioning without Belly Board for Rectal Cancer : A Practical Dosimetric Study in a Resource-limited Setting

Background: This study aimed to evaluate the impact of patient positioning on dose distribution to the bowel and bladder in rectal cancer patients in a setting without access to a belly board or advanced techniques such as Intensity-Modulated Radiotherapy (IMRT). Methods: Between July and October 2014, 20 consecutive rectal cancer patients were prospectively enrolled. Computed Tomography (CT) simulations were performed with a full bladder in two positions: prone (without a belly board) and supine. Three-dimensional conformal radiotherapy (3D-CRT) plans delivering 46 Gy in 23 fractions were generated. Bowel volumes receiving 5-Gy increments (V5–V45) and bladder dose parameters were compared between positions. Results: The mean Planning Target Volume (PTV), bowel, and bladder volumes were similar between prone and supine positions (PTV: 1000.78 vs 1006.21 cm³, p=0.84; bowel: 752.04 vs 750.32 cm³, p=0.97; bladder: 225.48 vs 244.16 cm³, p=0.26). Across all dose levels (V5–V45), no statistically significant differences were observed in bowel or bladder irradiation. Conclusion: Although these findings do not introduce new dosimetric concepts, they provide practical evidence supporting the use of the supine position with a full bladder in preoperative 3D-CRT for rectal cancer, particularly in centers lacking a belly board or access to IMRT. Supine positioning offers comparable bowel sparing, improved patient comfort, and better reproducibility, making it a feasible alternative in resource-limited settings.