驻留点权重标准差与施源器位置不确定性对宫颈癌患者剂量影响分析

摘要

目的 研究三维后装中驻留点权重标准差与施源器位置不确定性对宫颈癌患者受量影响.方法 选取已完成治疗的根治性宫颈癌患者20例,均使用Fletcher施源器(Nucletron # 189.730),基于原CT图像和结构信息,重新设定一组新计划,记录原计划和新计划中驻留点权重并计算驻留点权重标准差(DWSD),按照DWSD大小患者2个计划被分成高低两组,即LDWSD组(0.141～0.299)和HDWSD组(0.211～0.337),利用Oncentra(R)Brachy V4.3计划系统模拟Fletcher施源器中宫腔施源器,阴道施源器发生±1 mm位移时的剂量分布.统计CTV的D100、D90和V150,、膀胱、直肠、小肠的D0.1cc、D1cc和D2cc,分析DWSD与施源器位置不确定性对三维后装剂量的影响.结果 DWSD越大,由施源器位置不确定性产生的剂量偏差就越大.当宫腔施源器、阴道施源器发生1 mm位移时,CTV的HDWSD组D100、D90、V150比LDWSD组分别高3.0％、23.8％、4.8％和0.5％、1.2％、5.2％,膀胱、直肠、小肠HDWSD组D0.1cc、D1cc、D2cc都高于LDWSD组,其中小肠最明显,分别高44.0％、22.8％、16.8％和10.3％、14.4％、12.4％.结论 宫颈癌三维后装计划的评估应考虑驻留点权重因素,可以减小由施源器位置不确定导致的剂量偏差.%Objective To investigate the dosimetric influence of dwell weight standard deviation (DWSD) and applicator displacement in cervical cancer patients treated with three-dimensional brachytherapy.Methods A total of 20 cervical cancer patients who had completed radical treatment were selected in this study.The Fletcher applicator (Nucletron#189.730) was used for these patients.A new plan,based on the former CT images and structures,was designed for each patient.In former and new plans,dwell weight was recorded,and DWSD was calculated.Two groups,low-DWSD (LDWSD,0.141-0.299) and high-DWSD (HDWSD,0.211-0.337),were set according to the DWSD size for the two plans.Dosimetric effects from ± 1 mm displacement of tandem applicator or ovoid applicator were simulated with Oncentra (R) Brachy V4.3 treatment planning system.D100,D90,and V150 for clinical target volume (CTV)and D0.1cc,D1cc,and D2cc for the bladder,rectum,and sigmoid were evaluated.Dosimetric comparisons were made between the LDWSD group and HDWSD group to study the dosimetric effects of DWSD and applicator displacement in cervical cancer patients.Results The dosimetric effects from applicator displacement increased with increasing DWSD.If there was a 1 mm displacement of tandem applicator or ovoid applicator,D100,D90,and V150 of CTV were 3.0％,23.8％,and 4.8％ higher or 0.5％,1.2％,and 5.2％ higher in the HDWSD group than in the LDWSD group;D0.1cc,D1cc,and D2cc of the bladder and rectum were significantly higher in the HDWSD group than in the LDWSD group,particularly for the sigmoid (up 44.0％,22.8％,and 16.8％) and (up 10.3％,14.4％,and 12.4％).Conclusions DWSD should be considered in plan evaluation for cervical cancer patients treated with three-dimensional brachytherapy.The dosimetric influence from applicator displacement can be decreased by reducing DWSD properly.