CT设备的扫描电压对放疗计划剂量计算的影响

Influence of scanning voltage of CT equipment on dose calculation of radiotherapy treatment planning

目的探讨CT设备的扫描电压对常规放疗计划系统在靶区剂量计算影响的研究.方法用已知的电子密度CIRS062模体,在64排CT上扫描两组CT图像电压分别为120KV及140KV,建立两组CT-相对电子密度曲线(computed tomography number-relative electron density,CT-RED)并进行分析.选择临床病例24例,乳腺癌、宫颈癌及骨转移各8例.每个临床病例分别用上述两种CT-RED曲线进行两次计划设计,计划设计的处方剂量及函数等参数保持一致,比较计划剂量计算的结果差异.结果CT-RED曲线的CT值均随着材料电子密度的增大而增大;电子密度在0~1.117之间CT值差异非常小,电子密度在1.117及以上的区间,两条曲线CT值差异越来越大.在计划中乳腺癌、骨转移及宫颈癌患者PTV的Dmean及机器跳数均有不同程度的差异,其中在电子密度较大的骨转移靶区剂量差异较大,但统计学并无显著差异(P>0.05).结论在常用的CT扫描电压下对人体范围之内的电子密度常规计划靶区剂量并无显著影响的.

Objective To study the influence of scanning voltage of computed tomography(CT)equipment on dose calculation in target area of conventional radiotherapy planning system.Methods The known electron density CIRS062 module was used to scan two sets of CT images with the voltage of 120KV and 140KV respectively on the 64-slice CT.Two CT number-relative electron density(CT-RED)curves were established and analyzed.Twenty-four clinical cases were selected,including 8 cases of breast cancer,8 cases of cervical cancer and 8 cases of bone metastasis.In one clinical case,the two CT-RED curves were used for planning design twice,and the prescription dose and function parameters of the planned design were consistent,and the difference in the calculation results of the planned dose was compared.Results The CT values of CT-RED curve increased with the increase of electron density.The difference of CT values between 0 and 1.117 is very small,and the difference of CT values between the two curves becomes larger when the electron density is greater than 1.117.The Dmean and machine jump count(MU)of PTV in patients with breast cancer,bone metastasis and cervical cancer had different degrees of difference in the plan,among which the dose difference in bone metastasis target area with high electron density was large,but there was no statistically significant difference(P>0.05).Conclusion The conventional CT scanning voltage has no significant effect on the conventional planned target dose of electron density in the range of human body.