Comparison of different evaluation programs for the verification of patient irradiations with tomotherapy

Three different evaluation programs used to verify patient irradiations with tomotherapy were checked. All programs compare a planned dose distribution with the measured dose distribution using radiochromic film. The evaluation programs differ in quality, time effort and user friendliness. One evaluation program is offered by TomoTherapy Inc. and implemented in the Tomotherapy treatment planning station, the other two programs are in-house developments. The TomoTherapy solution is based on radiographic films. It could be shown that radiochromic films can also be used for the evaluation using the TomoTherapy treatment station, but this method has some drawbacks concerning user friendliness, time effort and quality. The scanned image files could not be applied directly, an extra computer program had to be written which converted the red channel of an RGB-Tiff image into a specific format used by the TomoTherapy planning station. The required marking on the film to show the location of the film introduces an uncertainty, which influences the γ index and dose profile. In addition the program lacks the possibility to visualize 2D dose-difference images, so that the other two methods are more suitable. The two other programs EasyQ and the program based on direct Matlab routines use an automatic registration based on a least square minimization. They have quite similar results considering the absolute dose difference. The EasyQ program has the advantage to offer much more evaluation methods. Comparison of all three evaluation methods shows that the Matlab evaluation program is best suited for the verification of patient irradiations. Produced images are easy to understand and can be interpreted with little effort. The Matlab evaluation is the program used in clinical routine at our site.