WE‐C‐BRB‐02: Independent Two‐Dimensional Dose Validation for TomoTherapy

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.