早期NSCLC无均整器模式VMAT计划剂量比较研究

The comparison of plan dose and dose verification in volumetric modulated arc therapy for early stage non-small cell lung cancer with non-flattening filter

通过对比传统均整器（FF）模式剂量分布,研究无均整器（FFF）模式下VMAT计划对早期NSCLC的剂量分布特点,及通过三维剂量验证系统来验证TPS对FFF模式的剂量计算精度。方法 采用美国瓦里安公司TrueBeam加速器和Eclipse TPS,对2015年间收治的20例接受SBRT的早期NSCLC病例,采用4DCT模拟定位和平均密度法重建三维结构并勾画轮廓;基于同样设备参数进行FF和FFF模式VMAT的计划设计,比较靶区和OAR剂量体积参数。采用ArcCheck的DVH进行三维剂量验证和中心点绝对剂量验证,并进行两种模式计划验证结果的配对t检验。结果 两种模式CI100%基本一致（P=0.82）,FFF模式CI80%、CI50%低于FF模式（P=0.02、0.01）。患侧肺、全肺受量FFF模式明显减少（P均〈0.01）。两种模式机器跳数相近（P=0.34）,但FFF模式出束时间明显少于FF模式（P〈0.01）。两种模式的DVH总通过率、γ通过率、中心点绝对剂量偏差值均相近（P=0.05、0.16、0.26）。结论 对早期NSCLC患者VMAT计划采用FFF模式比FF模式能改善剂量分布适合度,减少肺受量及患者治疗中体位变化对靶区及OAR受量的影响。通过DVH三维剂量验证证明Eclipse TPS对基于FFF的VMAT剂量计算精度能满足临床要求。

Objective To compare the dose distributions of the volumetric modulated arc therapy （VMAT） for early stage non-small cell lung cancer （NSCLC） using conventional flattening filter （FF） and the flattening filter free （FFF） beams and to verify the dose calculation accuracy of the FFF beam through a three-dimensional verification system. Methods The treatment plans of 20 patients （2015 years hospitalized） treated with SBRT for early stage NSCLC using a TrueBeam accelerator were retrospectively analyzed. The patients were scanned with 4DCT and the average density projection images were used for organ segmentation and treatment planning using an Eclipse plan system. Two volumetric modulated arc therapy （VMAT） plans with FF and FFF were designed with the same planning parameters for each patient. The dose distributions between the two plans were compared and their dose verifications were assessed with the ArcCheck device. Results With the same dose coverage for the target,there was no significant difference in the dose compatibility index 100%（CI100%） between FF and FFF beams （P=0.82）.CI80% and CI50% of FFF plan were lower than that of FF plan （P=0.02,0.01）.The dose significantly decreased in the FFF plan comparing with the FF plan for the ipsilateral lung and the total lung （P〈0.01 for both）.There was no significant difference between monitor units of the FF and FFF plans （P=0.34）,while the delivery time of FFF was significant shorter than that of FF （P〈0.01）.The DVH passing,γ pass rates and the absolute dose deviations of the FF and FFF plans at the central point were not significantly different （P=0.05,0.16,0.26）. Conclusions FFF beams for NSCLC patients with VMAT planning can significantly improve the dose distribution compatibility and reduce radiation doses to lung. The beam delivery with FFF beams was also faster. Furthermore,the three-dimensional dose verification confirmed that the dose calculation in Eclipse plan system using FFF beams for VMAT plans were accurate and met the clinical need.