Comparison of prone versus supine position in assessment of small bowel and rectal dose in pelvic radiotherapy for carcinoma cervix

Background: Pelvic irradiation for cervical cancer is frequently associated with gastrointestinal and genitourinary toxicities due to radiation exposure to adjacent organs at risk (OAR). Optimizing patient positioning and organ preparation may reduce these effects. Aims and Objectives: This prospective study evaluated the dosimetric impact of prone versus supine positioning during pelvic radiotherapy planning in patients with cervical cancer. Materials and Methods: A total of 40 patients with FIGO stage II–III cervical cancer undergoing curative pelvic radiotherapy were prospectively enrolled. Each patient underwent contrast-enhanced computed tomography simulation in both prone (with belly board) and supine positions using standardized bowel and bladder preparation. Target volumes and OAR were contoured, and position-specific plans were generated using institutional techniques (intensity-modulated radiotherapy, three-dimensional conformal radiotherapy, and arc therapy) with uniform planning objectives. Dose–volume parameters for OAR and target volumes were compared, and correlations were analyzed, with P<0.05 considered statistically significant. Results: Stage II disease was present in 36 of 40 patients (90%). Prone positioning significantly reduced the small bowel dose compared with the supine position (25.15 vs. 29.36 Gy; P=0.004), while doses to the bladder, rectum, clinical target volume (CTV), and planned target volume (PTV) did not differ significantly between positions (P>0.05). A significant correlation between bladder and small bowel doses was observed in the prone position (ρ=0.606; P=0.002), but not in the supine position. Small bowel doses did not vary significantly across radiotherapy techniques, whereas bladder, rectum, CTV, and PTV doses showed significant differences (P<0.05). Conclusion: Prone belly board positioning significantly reduced the small bowel dose without compromising target coverage in patients undergoing pelvic radiotherapy for cervical cancer. Bladder and small bowel doses were significantly correlated in the prone position.