IMRT计划剂量误差与射野特征参数相关性分析

目的 研究调强计划射野特征参数之间的关系,以及射野特征参数对调强计划绝对剂量验证准确性的影响.方法 使用Pinnacle 7.6c治疗计划系统,直接子野优化方法设计43例调强放射治疗计划,移植到固体水模.使用0.13 cc Farmer型标准电离室(IBA Corp),DOSE1剂量仪测量绝对剂量.统计43例调强病例的射野特征参数,分析其相互关系,并统计验证误差,分析射野特征参数与验证结果的相关性.结果 各射野特征描述参数之间存在相互联系(P＜0.05).测量偏差与各射野特征参数均显著相关.子野数大于80个的IMRT计划,剂量偏差值大于3％；子野数小于80,多数计划的剂量偏差值小于3％.子野数大于100个的IMRT计划,一部分计划的剂量偏差值大于4％；子野数小于100个时,剂量偏差值均小于4％.结论 从治疗计划设计角度而言,应在临床可以接受的情况下,尽量减少总射野数和总子野数,总子野数应控制在80个以内,可减少调强放疗计划验证偏差.

Pertinence analysis of intensity-modulated radiation therapy dosimetry error and parameters of beams

Objective To study the relationship between parameter settings in the intensity-modulated radiation therapy (IMRT) planning in order to explore the effect of parameters on absolute dose verification.Methods Forty-three esophageal carcinoma cases were optimized with Pinnacle 7.6c by experienced physicist using appropriate optimization parameters and dose constraints with a number of iterations to meet the clinical acceptance criteria. The plans were copied to water-phantom, 0.13 cc ion Farmer chamber and DOSE1 dosimeter was used to measure the absolute dose. The statistical data of the parameters of beams for the 43 cases were collected, and the relationships among them were analyzed. The statistical data of the dosimetry error were collected, and comparative analysis was made for the relation between the parameters of beams and ion chamber absolute dose verification results.Results The parameters of beams were correlated among each other. Obvious affiliation existed between the dose accuracy and parameter settings. When the beam segment number of IMRT plan was more than 80, the dose deviation would be greater than 3%; however, if the beam segment number was less than 80, the dose deviation was smaller than 3%. When the beam segment number was more than 100, part of the dose deviation of this plan was greater than 4%. On the contrary, if the beam segment number was less than 100, the dose deviation was smaller than 4% definitely.Conclusions In order to decrease the absolute dose verification error, less beam angles and less beam segments are needed and the beam segment number should be controlled within the range of 80.