Eclipse系统中通量平滑对单发脑转移瘤调强放疗的剂量学影响研究

目的:探讨Eclipse计划系统中不同的通量平滑值在单发脑转移瘤调强放疗(intensity modulated radiotherapy,IMRT)中的剂量学差异。方法:随机选取20例单发脑转移瘤患者的临床资料,基于Eclipse v13.6计划系统和Varian Trilogy加速器为每个患者制订6组逆向IMRT计划。使用默认的X、Y方向通量平滑值X=40、Y=30作为对照组,其他5组在相同的优化条件下,改变X、Y方向的通量平滑值分别为X=0、Y=0,X=20、Y=15,X=80、Y=60,X=100、Y=80,X=200、Y=150重新进行计划设计和评估。比较各计划靶区的D2、D98、Dmean和适形性指数(conformity index,CI)、均匀性指数(homogeneity index,HI),危及器官(organs at risk,OAR)的剂量学参数脑干Dmax、视神经Dmax、视交叉Dmax、晶体Dmax、眼球Dmax及各计划的机器跳数和Gamma通过率。采用SPSS 22.0进行统计学分析。结果:与对照组相比,X=0、Y=0和X=20、Y=15计划组的D2有统计学差异(P<0.05),所有组的D98均有统计学差异(P<0.05),X=0、Y=0和X=200、Y=150计划组的Dmean有统计学差异(P<0.05),所有计划组的CI均有统计学差异(P<0.05),X=100、Y=80和X=200、Y=150计划组的HI有统计学差异(P<0.05)。与对照组相比,所有计划组脑干Dmax、视神经Dmax、眼球Dmax均无统计学差异(P>0.05);对照组的晶体Dmax低于X=80、Y=60,X=100、Y=80,X=200、Y=150计划组(P<0.05);对照组的视交叉Dmax低于X=100、Y=80和X=200、Y=150计划组(P<0.05)。随着通量平滑值的增加,机器跳数减少,Gamma通过率增加。结论:综合考虑单发脑转移瘤IMRT的临床需求和计划执行效率,X、Y方向通量平滑值建议采用默认的X=40、Y=30为佳。

Dosimetric study of fluence-smoothing on single brain metastases IMRT based on Eclipse system

Objective To compare the dosimetric differences of fluence-smoothing parameters in the Eclipse planning system in intensity modulated radiotherapy (IMRT) of single brain metastases. Methods Totally 20 patients with solitary brain metastases were randomly selected and 6 groups of inverse IMRT plans were developed for each patient based on the Eclipse v13.6 planning system. The plans with the default fluence-smoothing values of X=40 and Y=30 in the X and Y directions were used as the control group, while the other 5 groups were formed under the same optimized conditions by changing the flux smoothing values in the X and Y directions to X=0 and Y=0, X=20 and Y=15, X=80 and Y=60, X=100 and Y=80, and X=200 and Y=150, respectively. All the plans were compared for target volume parameters including D2, D98, conformity index (CI) and homogeneity index (HI), Dmax of brainstem, optic nerve, optic chiasm, lens and eyeball at risk, monitor unit as well as Gamma pass rate. SPSS 22.0 was used for statistical analysis. Results There were significant differences between the D2 value of the control group and those of the groups of X=0 and Y=0, X=20 and Y=15 (P<0.05);there were statistical differences between the D98 values between all the groups (P<0.05);there were obvious differences between the Dmean values of the groups of X=0 and Y=0, X=200 and Y=150 (P<0.05). There were significant differences between the CI values of the groups (P<0.05), and the differences of the HI values were statistically significant between the groups of X=100 and Y=80, X=200 and Y=150 (P<0.05). The control group had no obvious differences with the other groups in the Dmax values of the brainstem, optic nerve and eyeball (P>0.05), which had the lens Dmax value significantly lower than those of the groups of X=80 and Y=60, X=100 and Y=80, and X=200 and Y=150 (P<0.05), and the optic chiasm Dmax value statistically lower than those of the groups of X=100 and Y=80, X=200 and Y=150 (P<0.05). As the flux smoothing value increased, the number of monitor units decreased while the Gamma pass rate rose. Conclusion The default flux smoothing values of X=40 and Y=30 are recommended in the X and Y directions with considerations on the clinical requirements and plan implementation efficiency of single brain metastases IMRT.