最小机器跳数对非小细胞肺癌调强放疗计划设计的影响

Effect of minimum monitor unit on the plan design of intensity- modulated radiotherapy for non-small cell lung cancer

目的:探讨非小细胞肺癌(NSCLC)调强放疗(IMRT)计划设计中最小机器跳数(MMU)对计划质量的影响,为在计划设计时MMU的设置提供参考。方法:选取10例NSCLC病例在Pinnacle治疗计划系统(TPS)进行IMRT设计。MMU分别取5、8、10、12、15、20、25,每个患者共得到7个计划。IMRT的优化目标与约束条件与MMU为5的计划保持一致。通过剂量体积直方图评估后,统计分析各IMRT计划中靶区和危及器官的剂量分布相对M1092MU为5的计划的差异。结果:随着MMU的增加,靶区V_(95%)和CI小幅降低,D_(mean)和HI小幅增加,但仅在MMU=25时,V_(95%)、CI和HI的差异有统计学意义(P<0.05);危及器官(如脊髓、心脏、双肺等)的剂量分布并未出现显著差异(P>0.05),脊髓的最大剂量D_(max)略有上升,最多可增加208 c Gy(5.4%)。随着MMU的增加,IMRT计划的总子野数显著减少(P<0.05),而机器总跳数也随着减少,当MMU>15时,差异有统计学意义(P<0.05);总子野数与机器总跳数呈强相关(r=0.725,P<0.01)。结论:在使用TPS设计肺癌IMRT计划时,可适当提高MMU,在并不引起靶区及危及器官剂量分布的显著改变的同时,可以达到减少子野数量和机器总跳数、缩短治疗时间、提高治疗传输效率的效果。

Objective To provide some references for the setup of minimum monitor unit （MMU） during the plan design of intensity-modulated radiotherapy （IMRT） for non-small cell lung cancer （NSCLC） by evaluating the effect of MMU on the IMRT plan quality. Methods IMRT plans were designed in Pinnacle treatment planning system （TPS） for 10 selected NSCLC patients. Each patient received 7 plans with the MMU of 5, 8, 10, 12, 15, 20 and 25, respectively. The optimization objective and constraint condition of the IMRT plan with the MMU of 5 were consistent with those of the other IMRT plans. After evaluating the dose-volume histogram, the differences in the dosimetric distribution of target areas and organs at risk （OAR） between the IMRT plan with the MMU of 5 and the other IMRT plans were statistically analyzed. Results With the increase of MMU, the target V95./o and conformal index （CI） slightly reduced, while the mean dose and homogeneity index （HI） slightly increased, but only when MMU was 25, the differences in V95O/o, CI and HI between the IMRT plan with the MMU of 5 and the other IMRT plans were statistically significant （P〈0.05）. The dosimetric distribution of OAR （such as spinal cord, heart, lungs） did not showed any significant difference （P〉0.05）, but the maximum dose of spinal cord slightly increased, up to 208 cGy （5.4%）. With the increase of MMU, the number of segments of IMRT plans was significantly reduced （P〈0.05）, while the total monitor unit （MU） were also reduced, but only when the MMU was larger than 15 MU, the difference between the IMRT plan with the MMU of 5 and the other IMRT plans was statistically significant （P〈0.05）. The number of segments was strongly correlated to the total MU （r=0.725, P〈0.01）. Conclusion MMU can be appropriately raised when TPS is used to design IMRT plan for lung cancer, which does not cause a significant change of dosimetric distribution of target areas and OAR, but reduces the number of segments and the total MU, shortening the treatment time and improving the delivery efficiency.