Purpose: Whole breast irradiation is typically delivered in supine position. However, prone position delivery has also been proposed as an alternative technique for women with large breasts. The aim of this study was to compare the dosimetric results of whole breast irradiation delivered in prone and supine positions using helical Tomotherapy. Methods and Materials: Twenty patients with clinical stage 0‐II breast cancer underwent CT imaging in both supine and prone positions and were selected for treatment planning using the Tomotherapy Hi‐Art planning system. Dose‐volume histogram analysis was performed and the mean dose value as well as other dosimetric parameters of PTV and organs‐at‐risk (OAR) were compared in all patient cases. Results: In all twenty patient cases, the completed treatment plans were able to deliver at least 97% of the prescribed dose to PTV and the maximal dose was no larger than 108% in both supine and prone positions. The PTV coverage for prone position (97.98%) was slightly better (p=0.0009) than that of supine position (97.47%). There were no significant differences between the prone and supine positions in terms of hot spots and field homogeneity. The mean dose and V5 in OARs such as lung, heart and ipsilateral breast were significantly lower (29%–86% reduction depending on specific OAR) in prone position than in supine position plans. Conclusion: The prone‐position radiotherapy technique performed better than the supine‐position technique for breast cancer treatment in Tomotherapy with improved target coverage and lower incidental radiation doses to heart, lung and contralateral breast. However, comparing to the supine position technique, the prone‐position technique has limitations for big body size patients due to the requirement of positioning the prone board inside the bore of the Tomotherapy device.

Purpose: To develop a two‐dimensional (2D) dose calculation software for helical tomotherapy with absolute dose validation capability. Methods: This in‐house software takes advantage of archived patient treatment planning documents, initial coordinates of red and green lasers, central coronal plane slice numbers of the Cheese phantom, and clinical dosimetric functions. A tomotherapy DQA plan has to be generated and archived first. The software performs an independent absolute dose check to the tomotherapy plan. The software calculates the 2D dose map of the central coronal plane of the Cheese phantom, and the 2D map is narrowed into a 3.2cm×3.1cm rectangular on the plane to save calculation duration. Doses of points on the plane are calculated with 1 mm resolution, so that a total of 992 points are calculated for each patient case. The center of the 2D square is the cross point of red lasers, which is the center of the Cheese phantom by default. The 2D dose map calculated is thereafter compared with the planned one, which is a 3D dose matrix from the DQA plan. Gamma index is then calculated with 3mm and 5% criteria. Results: The newly developed software has been tested on ten tomotherapy patients (cases of 1 pancreas, 2 brain, 1 stomach, 1 lung, 1 head & neck, 3 prostate, and 1 esophagus). The gamma distributions are all passed with a minimum ratio of 95%. Conclusions: An in‐house independent dose calculation software for helical tomotherapy has been developed to independently validates 2D doses with gamma index. Gamma in this software is calculated by comparing the 2D calculation to 3D doses, which makes the introduced method more superior than normal IMRT or tomotherapy QA. Validation of the software on more cases and more tomotherapy units is necessary.