不同CT-RED校准曲线对肿瘤靶区和危及器官剂量分布的影响研究

Effects of CT-RED calibration curves of different simulators on dose distribution of tumor target and organs at risk

背景与目的:肿瘤部位的精准放疗取决于治疗靶区精准的剂量分布,探究使用不同计算机体层成像值-相对电子密度(computed tomography value to the relative electron density,CT-RED)校准曲线对计算各部位肿瘤剂量分布的影响,同时探索拟合一条CT-RED校准曲线的方法。方法:使用复旦大学附属肿瘤医院的两台CT定位机分别对CIRS-062型电子密度模体扫描,获得两组不同部位(头、胸、腹)临床扫描协议的CT-RED校准曲线,并综合各曲线优化出一条改良CT-RED曲线。使用原始及改良CT-RED曲线在治疗计划系统(treatment planning system,TPS)中分别计算各病例计划靶区(planning target volume,PTV)(鼻咽癌、肺癌和宫颈癌各16例)和危及器官(organ at risk,OAR)的剂量分布。最后在各肿瘤中选取5例来验证改良CT-RED曲线的可行性。结果:采用不同校准曲线计算出的剂量在腹部和头颈部中差异较小(<1.00%和<1.13%),但在肺部低密度区域有较大差异(2.50%);使用改良CT-RED曲线与标准CT-RED曲线分别计算头、胸和腹部肿瘤获得的剂量分布无显著差异(<1.00%)。结论:计算不同部位肿瘤的剂量分布应选取对应的CT-RED校准曲线。在具有多台CT定位机的中心也可选择改良CT-RED校准曲线方案以降低选错校准曲线的潜在风险。

Background and purpose:The precise radiotherapy of tumor site depends on the precise dose distribution of the therapeutic target.The purpose of this study was to explore the influence of different computed tomography value to the relative electron density(CT-RED)calibration curve on the dose distribution of tumor and the method of fitting one CT-RED curve.Methods:Two CT scanners in Fudan University Shanghai Cancer Center were used to scan the CIRS-062 electronic density phantom,the CTRED calibration curves of different sites(head,chest and abdomen)were obtained,and an improved CT-RED curve was optimized based on each curve.The original and modified CT-RED curves were used to calculate the dose distribution of planning target volume(PTV)(nasopharyngeal cancer,lung cancer and cervical cancer,16 cases of each)and organ at risk(OAR)in the treatment planning system(TPS).Finally,5 cases of each tumor were selected to verify the feasibility of optimized CT-RED.Results:The dose calculated by different CT-RED curves showed minimal differences in cervical cancer and head and neck tumor(<1.00%and<1.13%),but there was a large difference(2.50%)in low-density area of lung tumor.There was no significant difference(<1.00%)between the optimized CT-RED curve and the original six CT-RED curves in the PTV and OAR.Conclusion:The corresponding CTRED calibration curve should be selected to calculate the dose distribution of different tumors.And the improved CT-RED calibration curve scheme can also be used to reduce the potential risk of wrong calibration curve selection in the center with multiple positioning CT.