肺癌螺旋断层放疗计划设计中应用Block减少肺低剂量区的研究

目的: 研究非小细胞肺癌螺旋断层放疗计划设计中应用Block降低肺低剂量区的方法。 方法:选取20例非小细胞肺癌病例，对每例病例勾画保护区域作为Block，并按以下3种不同的Block设置方式设计放疗计划。第I组采用Unblock方式，第II组采用Directional Block方式，第III组采用Complete Block+Directional Block方式。优化结果满足靶区和危及器官剂量限值后，比较3组方案计划靶区和肺组织剂量分布、剂量体积直方图（DVH）和单次治疗时间，用单向方差分析方法（One-Way ANOVA）对相关数据的差异性进行统计学分析。 结果:I到III组，双肺V5依次为（51.3±6.5）%、（37.4±5.0）%、（26.5±2.9）%，双肺平均剂量（MLD）依次为（10.4±0.5）%、（9.4±0.8）%、（8.2±1.0）%。将第II组和第III组分别与第I组进行比较，双肺V5分别降低了27%、48%，双肺MLD分别降低了9.6%、21%。V5和MLD明显降低，差异具有统计学意义。与此同时，PTV剂量均匀性变差，均匀性指数依次为0.065±0.003、0.082±0.006、0.084±0.011，差异具有统计学意义。PTV适形度指数依次为0.77±0.07、0.69±0.09、0.62±0.08，差异不具有统计学意义。I到III组的治疗时间依次为（5.5±0.5）、（11.8±0.6）、（16.3±2.3） min，第II组和第III组的治疗时间分别是第I组的2.1倍和2.9倍。 结论:非小细胞肺癌螺旋断层放疗计划设计时，运用Complete Block和Directional Block能够有效减少正常肺组织V5的体积，同时可以降低MLD，但靶区的均匀性和适形性会受一定影响（仍符合临床要求），治疗时间也会相应变长。

Applying Block to reduce low-dose volume of lungs in helical tomotherapy of lung cancer

Abstract: Objective To study the method of reducing the low-dose volume of lungs by Block in helical tomotherapy of non-small cell lung cancer. Methods Twenty cases of non-small-cell lung cancer were selected in this study. For each case, the protected area was plotted as Block and the radiotherapy plan was designed according to the 3 different Block settings. Unblock mode was adopted in group I, Directional Block mode in group II, Complete Block+Directional Block mode in group III. After the optimization results met the dose limits of target areas and organs-at-risk, the dose distribution, dose-volume histogram and single treatment time were compared among 3 groups, and one-way ANOVA was used to analyze the differences of the relevant data. Results The V5 of lungs was (51.3±6.5)%, (37.4±5.0)%, (26.5±2.9)% in group I, II and III, respectively, and mean lung dose (MLD) was (10.4±0.5)%, (9.4±0.8)%, (8.2±1.0)%, respectively. Compared with those in group I, the V5 of lungs in group II and III was reduced by 27%, 48%, and MLD was decreased by 9.6%, 21%, respectively, with statistical differences. The homogeneity index of planning target volume (PTV) was 0.065±0.003, 0.082±0.006 and 0.084 ± 0.011 in group I, I and III, respective, and the difference was statistical significant. The conformity index of PTV was 0.77±0.07, 0.69±0.09 and 0.62±0.08 in group I, II and III, without statistical significance. The treatment time of group II and group III was (11.8 ± 0.6), (16.3 ± 2.3) min, respectively, which was 2.1 times and 2.9 times longer than (5.5±0.5) min in group I. Conclusion The use of Complete Block and Directional Block can reduce the V5 of normal lung tissue and decrease MLD, but affect the homogeneity index and conformity index of PTV (still meet the clinical requirements) and prolong the treatment time.