初治鼻咽癌VMAT与IMRT的比较评估

Comparison and evaluation of VMAT and IMRT for the treatment of initial treated nasopharyngeal carcinoma

目的比较初治鼻咽癌（NPC）子野式调强放疗（ss-IMRT）和容积调强弧形治疗（VMAT）的计划质量、治疗效率和执行精度，为临床治疗技术的选择提供参考依据。方法对26例NPC患者以相同处方剂量和目标条件分别设计9个野SS—IMRT和VMAT计划。比较两种计划剂量分布和剂量适形指数（CI）与均匀性指数（HI），不同危及器官（OAR）的平均剂量、最高剂量或感兴趣剂量体积等，治疗计划执行时间以及治疗计划剂量验证准确性。结果两种治疗计划均能满足临床剂量要求，VMAT计划的靶区剂量覆盖率略差于ss—IMRT。ss—IMRT和VMAT的CI、H1分别为0．57、0．08和0．48、0．12（t=-4．52、-8．33，P=0．000、0．000）。除脑干外，VMAT计划各OAR的平均剂量和最高剂量均高于SS—IMRT计划（t=-9．57～-3．71，P=0．000～0．001），其中脊髓D1cc和腮腺D50％的分别平均增高了11．9％和6．5％。SS—IMRT和VMAT治疗时间分别为803．7S和389．3S（t=24．12，P=0．000），VMAT减少了51．6％。SS—IMRT和VMAT的3mm／3％的1通过率分别为99．4％和98．0％（t=5．19，P=0．000）。结论初治鼻咽癌VMAT的剂量分布可满足临床要求但略差于9个野SS—IMRT，同时具有高效和剂量准确的优点。

Objective To compare planning quality, treatment efficiency and delivery accuracy for initial treated nasopharyngeal carcinoma （NPC） with step ＆ shoot intensity modulated radiation therapy （ ss- IMRT） and volumetric modulated arc therapy （VMAT）. These results will help make a clinic choice of the therapeutical technique. Methods Twenty-six NPC cases were planned with the same dose prescription and objective constrains by means of 9-field ss-IMRT and VMAT respectively. Compare： （ 1 ） plan dosimetric distribution, conformity index and homogeneity index of the targets, the average dose, maximum dose and interested dose-volume histograms of organs at risk （OAR） et al; （2） delivery times of the therapy plans ; （3） the accuracy of treatment plans dose verification. Results Both therapeutical plans can achieve the clinic dosimetric demands. Compared to ss-IMRT, VMAT had less inferior target coverage. The CI and HI of the PGTV was 0. 57 and 0. 08 （ss-IMRT） , 0. 48 and 0. 12 （VMAT） respectively （t = -4. 52, -8.33, P =0. 000, 0. 000）. Except of brain stem, VMAT had higher mean dose and maximum dose of OARs than ss-IMRT （t= -9.57 - -3.71,P= 0.000 -0.001）. The spinal cord D1cc and parotids D50% were increased by 11.9% and 6. 5% averagely. The treatment times of ss-IMRT and VMAT were 803.7 s and 389. 3 s respectively （t =24. 12,P =0. 000）, while VMAT decreasing by 51.6%. The pass ratios of γ（3 mm,3% ） from the dose verification were 99.4% （ss-IMRT） and 98.0% （VMAT） respectively （t = 5.19, P = 0. 000）. Conclusions The dose distribution of VMAT for initial treated nasopharyngeal carcinoma can achieve the clinic demands, but slightly worse than 9-field ss-IMRT. VMAT has the advantage of high efficiency and dosimetric accuracy.