DOSIMETRIC COMPARISON OF PRE-SELECTED BEAM ORIENTATION AND BEAM ANGLE OPTIMIZATION IN INTENSITY MODULATED RADIATION THERAPY PLANS FOR NASOPHARYNGEAL CARCINOMA.

Abstract

Purpose: This study is intended to verify and analyze the dosimetric impact of Pre selected beam orientation (PSBO) and Beam angle optimization (BAO) in IMRT for Nasopharyngeal Carcinoma. Twenty patients of Nasopharyngeal carcinom Materials and Methods: a treated with IMRT Plans were recruited for this retrospective study. Varian Medical systems treatment planning systems (TPS), Eclipse of version 13.6 were used for planning. All twenty patients were treated with IMRT plan created by PSBO while choosing beam angle. Another plan using BAO used for choosing beam angles followed by PRO optimization for inverse planning were created. Objectives of PTV and OARs are maintained constant in both the plans. Statistical analyses of both the plans were performed using parameters; Paddick conformity index (PCI), Homogeneity index (HI), Dose delivered to OAR and Delivered MU. The statistical data were analyzed by Student t test. In this study, out of twenty patients, Result: seventeen patients BAO were valid for inverse planning optimization. For three patients beam angles chosen by BAO were invalid. And the dosimetric comparison of seventeen patients between BAO and PSBO was showing similar results except for MU. The p value obtained for all the parameters except MU, were >0.05. On taking into consideration of delivered MU, PSBO has lesser MU than BAO and are statistically signicant. Conclusion: On reviewing the results, it is concluded that both BAO and PSBO are clinically acceptable. But on concerning the delivered MU, PSBO seems to be better method than BAO. Also, it should be taken into account that three of the plans have been failed to optimize in BAO, since the beam angles suggested in this BAO method does not account the limitations of machine. It shows the advantage of PSBO over BAO. Hence, we can conclude that PSBO is a better method in selection of beam angles in Nasopharyngeal Carcinoma cases.