Neck skin dose planning for early-stage nasopharyngeal carcinoma: a comparative study of three radiotherapy methods

Abstract

Objective To compare the neck skin dose between fixed-field dynamic intensity-modulated radiation therapy (dIMRT), volumetric modulated arc therapy (VMAT), and helical tomotherapy (HT) in the treatment of early-stage nasopharyngeal carcinoma. Methods A total of 16 early-stage nasopharyngeal carcinoma patients undergoing radiotherapy were enrolled as subjects. The neck skin was delineated by contraction of the outer edge of neck by 3 mm. Dose planning was made by the traditional method (TP group) and a new method (NP group), in which the neck skin was considered as the organ at risk. Dmean and V5-V70 for the neck skin were recorded. The paired t-test was used to analyze the differences between two plans in each radiotherapy method. An analysis of variance was used to compare the same plan between the three radiotherapy methods. Results The HT group had significantly higher Dmean and V5-V70 for the neck skin than the dIMRT group and the VMAT group (P=0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.02). Using dIMRT, the Dmean and V10-V60 for the neck skin were reduced by 7%, 8%, 22%, 25%, 38%, 59%, and 85% in the NP group than in the TP group (P=0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00). Using VMAT, the Dmean and V20-V40 for the neck skin were reduced by 4%, 19%, 29%, and 34% in the NP group than in the TP group (P=0.02, 0.01, 0.02, 0.01). Using HT, the V30-V60 for the neck skin were reduced by 20%, 29%, 50%, and 67% in the NP group than in the TP group (P=0.00, 0.00, 0.00, 0.00, 0.03). Conclusions In the treatment of early-stage nasopharyngeal carcinoma, HT causes a higher radiation dose to the neck skin than dIMRT and VMAT, while dIMRT and VMAT have similar neck skin doses. The neck skin dose can be significantly reduced with the neck skin as the organ at risk. Key words: Nasopharyngeal neoplasms/dynamic intensity-modulated radiation therapy; Nasopharyngeal neoplasms/volumetric modulated arc therapy; Nasopharyngeal neoplasms/helical tomotherapy; Skin dose