宫颈癌腔内放疗分次间靶区及OAR剂量研究

Interfractional dosimetric study of target volume and organs at risk following intracavitarybrachytherapy for cervical cancer

目的 分析三维正、逆向、二维计划模式下宫颈癌腔内放疗分次间剂量变化,探讨短间隔内非同次施源器置入术隔次计划实施的风险。方法 回顾比较我科收治的11例根治性放疗宫颈癌患者的25组间隔≤4 d的连续2次CT引导下腔内放疗计划。将同一组内前次腔内放疗计划（Plan-1）的驻留位置和时间模拟至后次腔内放疗CT图像上形成Plan-1-S,记录3种计划模式下的靶区覆盖指标及OAR的D 2 cc,并与后次实际计划（Plan-2）比较。采用配对t检验、Wilcoxon符号秩检验及方差分析。结果 逆向模式Plan-1-S的高危CTV的D90、D100、V100较实际计划分别下降（-9.11±13.46）%、（-13.16±18.79）%、（-7.80±13.34）%（P=0.002、0.002、0.005）。逆向模式隔次计划D90、D100、V100下降比例最高,分别为76%、80%、76%,D90、D100、V100最大下降值分别332.14 cGy （二维）、244.12 cGy （正向）、41.76%（逆向）。正向模式下OAR超量比例最高,D90、D100、V100下降伴1个OAR超量分别占29.41%、37.50%、25.00%,伴2个OAR超量分别占5.88%、12.50%、6.25%。小肠是超量最多器官,发生率达36%。3种模式比较中,逆向计划各靶区覆盖指标下降程度较二维计划最大。结论 无论哪种计划模式,即使短间隔,隔次模拟计划均有明显降低靶区覆盖、增加OAR超量发生的高风险,不建议临床应用。

Objective To examine the interfractional dosimetric variations among inverse three-dimensional （3D） plan, forward 3D plan, and two-dimensional （2D） plan of intracavitary brachytherapy for cervical cancer, and to discuss the risk of implementing the interval plan on different implantation applicators at short time intervals. Methods Twenty-five groups of CT-guided intracavitary brachytherapy （two consecutive radiations at ≤4 d apart） plans from 11 cervical cancer patients who received radical radiation therapy in our hospital were reviewed and compared. The dwelling location and time of the first intracavitary brachytherapy plan （Plan-1） were simulated on the CT image of the second intracavitary brachytherapy to form Plan-1-S. The target coverage indices and D 2 cc of organs at risk （OARs） of Plan-1-S and Plan 2（actual plan of the second intracavitary brachytherapy） under the three planning modes were recorded and compared using the paired t-test, Wilcoxon signed rank test, and ANOVA. Results The D90, D100, and V100 of high-risk CTV were significantly lower in Plan-1-S created under the inverse mode in the actual plan （-9.11±13.46%,-13.16±18.79%, and -7.80±13.34%, P=0.002, 0.002, and 0.005, respectively）. D90, D100, and V100 of the interval plan had the greatest reduction under the inverse mode （76%, 80%, and 76%, respectively）. The maximum reductions in D90, D100, and V100 were 332.14 cGy （2D）, 244.12 cGy （forward）, and 41.76%（inverse）. OAR overdose occurred most frequently under the forward mode;the rates of D90, D100, and V100 reductions accompanied by one OAR overdose were 29.41%, 37.50%, and 25.00%, and the rates of D90, D100, and V100 reductions by two OAR overdoses were 5.88%, 12.50%, and 6.25%,respectively. Overdose occurred most frequently in the small intestine （36%）. Comparison of the three planning modes showed that the inverse plan had a greater reduction in each target coverage index than the 2D plan. Conclusions The simulated interval plan can significantly reduce target coverage and increase the risk of OAR overdose regardless of the planning mode and the short time intervals, and is therefore not recommended for clinical application.