Application of AAPM Radiation Therapy Committee Task Group 23 test package for comparison of two treatment planning systems for photon external beam radiotherapy

Abstract

Task Group 23 of the AAPM Radiation Therapy Committee has produced a test package for verification of the accuracy of treatment planning for photon external beam therapy. The package includes measured fundamental beam data for 4 and 18 MV x rays, and 13 test cases with measured dose values at selected points, which serve as the reference for determination of calculated dose accuracy. Test cases include three square fields, two rectangular fields, a wedged field, a blocked field, and an irregular field, as well as cases of an off-center plane, source-to-SOURCE distance (SSD) variation, oblique incidence, and lung and bone inhomogeneities. This package was used to evaluate two treatment planning systems. Although average dose variations in most cases were less than 1%, maximum deviations up to 19% were observed in one planning system and up to 11% in the other. Dose deviations greater than 3% were observed for 51 of 532 points (in the 4 MV case) and for 124 of 586 points (in the 18 MV case). An additional component of the test package is an evaluation of radiological field width at different depths. The largest deviation for width was 17.4 mm for 4 MV and 9.1 mm for 18 MV. In 20% of the widths studied, the deviation observed was greater than 3 mm for the 4 MV case. In the 18 MV case 18% of the widths had deviations greater than 3 mm. Our data indicate that the accuracy of the two treatment planning systems tested here warrants improvement, even for simple treatment geometries involving photon beams, which are generally considered to be well understood. As one of the treatment planning systems is widely used in the US, it is concluded that the accuracy of the currently available commercial treatment planning systems is not adequate for achieving the generally stated goal of +/- 5% accuracy of dose delivery in radiation therapy. The AAPM Task Group 23 test package provides an extremely useful tool for a quantitative analysis of treatment planning systems for photon beam radiation therapy.