Jaw tracking模式下不同铅门阈值对鼻咽癌VMAT计划的剂量学和计划复杂度分析

Research on Dosimetry and Planning Complexity of Different Jaw Threshold in VMAT of Nasopharyngeal Carcinoma Based on Jaw Tracking Technology

目的分析不同的铅门阈值对鼻咽癌容积旋转调强放疗(Volumetric Modulated Arc Therapy,VMAT)计划剂量学和复杂度的影响。方法采用Eclipse v13.5对15例鼻咽癌患者进行回顾性分析,每例患者制定4组VMAT计划(T-Half组、T1组、T2组和T-All组),其中T-Half组铅门采用半铅门技术,T1组铅门宽度15 cm,T2组铅门宽度18 cm,T-All组采用全铅门技术。评估4组计划剂量学结果及射束孔不规则度(Aperture Irregularity,AI)、调制复杂度因子(Modulation Complexity Score,MCS)、平均叶片运动路径(Average Leaf Trajectory,ALT)和机器跳数(Monitor Units,MU)。结果T-Half组肿瘤中危亚临床靶区(PCTV_(p2))的均匀指数(Homogeneity Index,HI)和V_(60)与T1组比较差异显著(P<0.05),T2组计划肿瘤靶区(PGTV_(69))的适形指数(Conformity Index,CI)、HI和PCTV_(p2)的V_(60)与T1组比较差异显著(P<0.05);脊髓的D_(max),双侧腮腺、喉和口腔的V_(30)及D_(mean)差异显著(P<0.05)。T-All组PGTV_(69)的CI、HI和D_(mean),肿瘤原发灶高危亚临床靶区(PCTV_(p1))的HI和PCTV_(p2)的V_(60)差异显著(P<0.05),双侧腮腺、脊髓D_(max)、喉和口腔的V_(30)与D_(mean)呈现显著差异(P<0.05)。4组计划AI无明显变化。随着铅门阈值增加,4组计划的MCS、ALT和MU总体呈现下降趋势,且随着铅门阈值增加,大面积射束孔占比也随之增加。结论半铅门模式并未改善靶区剂量学结果,但显著增加了计划MU。18 cm(T2)与全铅门模式降低了计划复杂度,但危及器官受照剂量显著增加,综合考虑计划质量与复杂度结果,铅门阈值为15 cm能满足鼻咽癌容积计划要求。

Objective To analyze the influence of the different jaw threshold on dosimetry and complexity of volumetric modulated arc therapy(VMAT)for nasopharyngeal carcinoma.Methods Eclipse v13.5 was used to retrospectively analyze 15 patients with nasopharyngeal carcinoma.Four VMAT plans were designed for each patient(T-Half group,T1 group,T2 group and T-All group).Half jaw technology was applied in T-Half group.The jaw width of T1 was set at 15 cm.The jaw width of T2 was set at 18 cm.The jaw width of T-All group was set at full jaw width.Dosimetric parameters,aperture irregularity(AI),modulation complexity score(MCS),average leaf trajectory(ALT)and monitor units(MU)of four groups were evaluated.Results Compared with T1 group,the HI and V_(60) of PCTV_(p2) in T-Half group showed statistically differences(P<0.05).For T2 group,the CI,and HI of PGTV_(69) and V_(60) of PCTV_(p2) showed statistically significant differences with group T1(P<0.05).The D_(max) of spinalcord,V30 and D_(mean) of parotid-L,parotid-R,larynx and oral were statistically significant differences(P<0.05).For T-All group,the CI,HI and D_(mean) of PGTV_(69),the HI of PCTV_(p1) and the V_(60) of PCTV_(60) were statistically significant differences(P<0.05).The D_(max) of spinalcord,V30 and D_(mean) of parotid-L,parotid-R,larynx and oral had significant difference(P<0.05).There was no significant change in planned AI among the four groups.With the increase of jaw width,the MCS,ALT and MU showed a decreasing trend,but the proportion of large-area aperture showed an increasing trend.Conclusion Half jaw technology can not improve the target dosimetry results,but can significantly increase the planned MU.The 18 cm(T2)and T-All can reduce the complexity of planning,but the dose of organs at risk is significantly increased.Considering the results of planning quality and complexity,the jaw threshold of 15 cm can meet the requirements of nasopharyngeal carcinoma volume planning.