Avaliação das correções de heterogeneidades no CAT 3D em planejamentos de tumores no pulmão

Abstract

This study aims to evaluate and quantify differences in the calculation of absorbed doses in PTV and healthy tissues by Pencil Beam algorithms without correction for heterogeneities and the Collapsed Cone with correction for heterogeneities available in the CAT 3D Planning System in lung treatments. Plans of ten patients treated with 3D conformational radiotherapy were analyzed. For each patient three planes were made. Plan 1 was performed with the Pencil Beam without correction of heterogeneities, plan 2 with Collapsed Cone with correction and plane 3 with Collapsed Cone with correction using the same monitor units calculated by plan 1, maintaining all the settings. The monitoring units, the isocenter doses, the distribution of isodoses, the doses in the PTV, the doses in the healthy tissues, the compliance indexes, the homogeneity indexes, the PTV compliance index, the index geometric. Statistical evaluation was performed using the Wilcoxon test. The results showed that the Collapsed Cone with correction requires on average less monitor units to deliver the prescribed dose compared to the Pencil Beam without correction. For both algorithms the 100% isodose loses coverage in PTV while the 15% isodose modeled by Collapsed Cone occupies higher volume in healthy tissues than the Pencil Beam. The mean PTV dose was the only parameter that did not vary significantly (PW 0.9218), with the algorithm change. The Collapsed Cone algorithm with correction covers a higher dose range than the Pencil Beam without correction. The mean doses in healthy tissues evaluated did not present significant variation in the algorithm change. The compliance index and the PTV compliance index suffer significant degradation in the algorithm change. The geometric index was the only parameter that observed a significant linear correlation for all the planes realized