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To compare organ-at-risk doses and setup reproducibility using the prone and supine orientations in volumetric modulated arc therapy VMAT for rectal cancer. All patients were treated using posteriorly-applied VMAT. Dose metrics for bladder and small bowel did not show significant differences between the prone and supine orientations.
Patient positioning in rectal cancer radiotherapy should be determined based on setup reproducibility and the position that yields the lowest radiation dose to the organs at risk OARs , especially the small bowel. Supine and prone positions are the most common treatment positions for rectal cancer patients undergoing radiotherapy. Previous studies have demonstrated that setup reproducibility for the different positions is an important influential factor of therapeutic outcomes 1 - 3. The supine setup is generally associated with more stability during irradiation, easier setup, and more patient comfort, while the prone setup, especially on a belly board, is associated with a reduced dose to the small bowel. Due to the steep dose distribution gradient in intensity-modulated radiation therapy IMRT , target dose coverage should be closely monitored. Although setup errors are accounted for in the margin expansion from clinical target volume CTV to planning target volume PTV , the margin is also affected by factors such as radiotherapeutic technique, treatment position, and the immobilization device; thus, the margin must be confirmed by practical outcomes. This study compared the effect of the supine and prone positions on target dose coverage, thereby providing a reference for the optimal position in rectal cancer IMRT. This study was conducted as a retrospective review.