Dosimetric Study Of Helical Tomotherapy In Supine And Prone Position For Postoperative Rectal Cancer Patients

[Objective] To compare the dose-volume relationship of small intestine, bladder and bilateral femoral head between different position(supine/prone) in helical tomotherapy for postoperative rectal cancer patients. To compare the set-up error of supine or prone position. To discusses the best position of helical tomotherapy for postoperative rectal cancer patients.[Method] Retrospectively analyzed a total of25patients of helical tomotherapy for postoperative rectal cancer in our department from Novermber2011to December2012, with11cases of supine group and14cases of prone group respectively.Unified regulations are set for target dose range and organ at risk limit in the CT images, to calculate on the TPS, and make a comparison of the dose-volume relationship of small intestine, bladder and bilateral femoral head in the two positions. According to the image matching of the MVCT before each treatment and KVCT in positioning to record the count of set-up error in X,Y and Z axis. To compare the set-up error of the two positions.[Results]1. No significant different was found either in the total volume of small intestine, bladder and bilateral femoral head, or in V40, V50of small intestine, the mean dose, V20, V30, V40, V50of bladder and the mean dose, V20, V30, V40of bilateral femoral head in this two groups.2. Compared with the supine group, the mean dose, V5, V10, V20, V30of small intestine was reduced significantly in prone group, which gives a statistically significance difference.3. The set-up error addition in each direction of the prone group is significantly greater than of the supine group, the difference has statistical significance. The set-up error of Y axis is largest, Z axis takes the second place, and X axis the least in supine; the set-up error of Y axis remains the largest, while X axis is larger than Z axis in prone.[Conclusion]The prone, with the belly-board, can obviously reduce the irradiation dose and volume percentage in patients of helical tomotherapy for postoperative rectal cancer, but it taken larger set-up error to compare with the supine. It should be choosed according to the actual situation in clinic.