The dosimetric comparison and evaluation of helical tomotherapy, volumetric-modulated arc radiotherapy (VMAT), step-and-shoot and sliding window radiotherapy techniques in nasopharyngeal carcinoma

The aim of this study was to dosimetrically compare treatment plans prepared with volumetric-modulated arc radiotherapy (VMAT), tomotherapy, step-and-shoot and sliding radiotherapy techniques in nasopharyngeal cancer (NPC) and to evaluate the superiority of different techniques in routine clinical practice. Treatment plans obtained by VMAT, tomotherapy, step and shoot and sliding window techniques were evaluated for twenty NPC patients. Different treatment plans were prepared by using the simultaneous integrated boost (SIB) technique in 35 fractions of 70Gy to primary planning target volume and 56Gy to elective lymph nodes. While NPC treatment plans were obtained in four different radiotherapy techniques, 95% of the target volumes were provided with defined dose coverage and critical organs received the lowest possible dose. In addition to the doses received by target tissues and critical organs, dose delivered time, monitor unit (MU), dose homogeneity (HI) and conformity (CI) index were compared for different radiotherapy techniques. The D-95 dose coverage and lowest maximum dose values (Dmax) are better achieved in the tomotherapy technique for primary tumor and elective lymph node target volumes. However, the lowest dose coverage is obtained in the step-and-shoot technique (p < 0.05). Although the highest MU value was calculated in tomo-therapy, the lowest delivered time was also achieved in the VMAT technique. It was observed that different radiotherapy techniques had advantages and disadvantages compared to each other at certain dose-volume constraints (D-max, D-min, D-mean,D- D-1, and V-30) for organs at risk. Although the tomotherapy technique was better in target volume dose coverage, it was observed that other techniques had superiority over each other in terms of protection of organs at risk and dosimetric parameters for NPC patients.