Examination of dosimetric study of four different volumetric modulated arc therapy (VMAT) plans in cases of head and neck cancer: Retrospective study

The purpose of this study is; to evalıuate conformity index (CI), homogeneity index (HI), critical organ doses, and monitor unit (MU) values in the treatment of head and neck cancer (H & N) cases by dosimetrically comparing 4 different volumetric modulated arc therapy and duration of treatment durations. The files of ten H & N were scanned and randomly selected in this study. The cross-sectional images were used for the patients virtual treatment plans were obtained with the Simens Somatom Emotion Duo Computerized Tomography (CT) device and transferred to the Monaco 5.1 Treatment Planning System (TPS). The plans with; one arc (VMAT1) with 3600 rotations, two arcs (VMAT2) starting from 1800 and rotating 3600 clockwise and reversely double arcs (kVMAT) starting from 1800 to 3600 double rotations one arc (2rVMAT) and 150-3450 collimator angles, were prepared. Four treatment plans had similar results in terms of PTV doses and was found to be clinically feasible. However in one case, the target volume of the VMAT1 plan was not obtained as it should be. In addition, the VMAT1 plan was found to have higher critical organ doses than other techniques. In particular, parotid gland dose has not been kept within the desired limits on the VMAT1 schedule more than one patients. PTV doses were similar among the other 3 treatment methods, but much lower critical organ dose results were obtained with the 2rVMAT technique. In comparison of treatment duration, the shortest treatment plan was VMAT1 and the longest treatment plan was the VMAT2 plan. As a result, four different treatment plans provide a good coverage of tumors. However, we believe that the 2rVMAT technique could be preferred because of the decreased doses in critical organ compared to the other tecniques. Key Words: Arc, H&N, Monaco TPS, VMAT