ABSTRACT
Objective To compare the neck skin dose between fixed-field dynamic intensity-modulated radiation therapy (dlMRT),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 D 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 D 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.
ABSTRACT
Objective The purpose of this study is to investigate the method to reduce the radiation dose to the neck skin in the Tomotherapy treatment plans for early-stage nasopharyngeal carcinoma.Methods The 17 patients with early-stage nasopharyngeal carcinoma that have been treated by the Tomotherapy were selected randomly for this skin sparing study.The neck skin sparing region was generated as an internal margin of 3 mm from the out body contour,excluding the intercrossed area with the targets.Candidate patients were planned using TP and NP method respectively:the TP group was planned with the traditional method.The new neck skin region was considered as an organ at risk (OAR) for planning dose constrain in NP group.The dosimetric metrics of targets and OARs,monitor units (MU) and delivery time were compared as the end points of these two groups.Results The two treatment plan groups satisfied the clinical requirement.There were no significant differences for D98,D95 and D2 of the targets (P ＞ 0.05).The Dmax of brainstem,D1cc of spinal cord,D of right parotid were higher in NP group than in theTPgroup (t =2.47,2.34,2.77,P＜0.05).The Dmax of left mandible joint was lower than TP group(t =2.30,P ＜ 0.05).The V30,V40,V50 and V60 of the skin were considerably lower than TP group (t =8.37,6.02,5.82,4.89,P ＜ 0.05).The mean MU and mean delivery time per fraction of NP group were 6.3％ and 8.1％ less than that of TP group respectively.Conclusions The neck skin region should be delineated as an OAR to be spared in the Tomotherapy treatment planning for early-stage nasopharyngeal carcinoma.This method can reduce the skin radiation dose effectively,alleviate the skin reaction,and improve the life quality of patients in radiotherapy.