加速器机架旋转加速度约束条件对VMAT计划的影响研究

目的 研究直线加速器机架旋转加速度设置，对多病种容积旋转调强（VMAT）计划剂量学、机器效率和计划验证结果的影响，探讨机器模型中机架加速度约束条件的优化选择。方法 分别选取10例鼻咽癌、非小细胞肺癌、乙状结肠腺癌腹膜后淋巴结转移和乳腺浸润性导管癌病例，在Pinnacle v9.10计划系统中建立允许机架旋转加速度变化和限制机架旋转加速度变化的两种机器模型，采用相同射野布置、优化目标参数和优化权重设计VMAT计划，分析各病种不同机架旋转加速度设置下靶区和危及器官剂量学变化，比较治疗时间和计划验证γ通过率的差异。结果 入组病例采用允许机架旋转加速度变化的机器模型：治疗时间显著低于机架匀速运动组（t=-6.751、-0.209、-19.523、-28.999，P<0.05），分别降低了15.27%、18.07%、19.71%和28.75%，同时影响靶区适形性和均匀性，但计划验证γ通过率均无统计学意义（P>0.05）；对于鼻咽癌病例，脑干计划危及器官（PRV）最大剂量增加1.25%；对于肺癌病例，脊髓最大剂量和全肺V₂₀增加了1.19%和1.21%，全肺V₅降低了1.21%；对于腹膜后淋巴结放疗病例，双侧肾脏、肝脏、小肠和结肠平均剂量均有增加；对于乳腺癌病例，患侧肺V₁₀增加了1.66%，健侧肺平均剂量降低了7.45%。结论 允许机架加速度变化模型设置可显著缩短计划治疗时间，提高治疗效率。虽一定程度上降低靶区适形性和均匀性，增加部分危及器官剂量，但仍符合临床剂量学要求。在Pinnacle v9.10机器模型机架加速度约束设置中，推荐使用允许机架变速运动设置。

Effects of gantry acceleration limitations on VMAT plans

Objective To study the effects of gantry acceleration limitations of a linear accelerator (linac) on the dosimetry of volumetric modulated arc therapy (VMAT) plans, machine efficiency, and dose verification result of VMAT plans and to explore the optimal selection of gantry motion models in the Pinnacle treatment planning system. Methods Ten cases of nasopharyngeal carcinoma, non-small cell lung cancer, sigmoid adenocarcinoma with retroperitoneal lymph node metastasis, and invasive ductal carcinoma of the breast were each selected for this study. Then two models were set up in the Pinnacle v9.10 treatment planning system, namely the one allowing gantry acceleration and the one limiting gantry acceleration. The same field arrangement, optimized target parameters, and optimized weights of VMAT plans were adopted in the two models, in order to analyze the dosimetric variations in targets and organs at risk (OARs) and compare the differences in treatment time and gamma passing rates. Results The treatment time of the enrolled patients under the model allowing gantry acceleration was significantly lower than that of the patients under the model limiting gantry acceleration was adopted (t=-6.751, -0.209, -19.523, -28.999; P< 0.05) and decreased by 15.27%, 18.07%, 19.71%, and 28.75%, respectively. Meanwhile, the conformity and uniformity of target areas were affected, while there was no statistical significance in the gamma passing rates in the validation of VMAT plans (P>0.05). For the cases of nasopharyngeal carcinoma (NPC), the maximum dose to brainstem PRV increased by 1.25%. For the cases of lung cancer, the maximum dose to the spinal cord and lung V₂₀ increased by 1.19% and 1.21%, respectively, while lung V₅ decreased by 1.21%. For the cases of sigmoid adenocarcinoma with retroperitoneal lymph node metastasis, the mean doses to bilateral kidneys, livers, small intestine, and colon all increased. For the cases of breast cancer, lung V₁₀ on the opposite side of cancer increased by 1.66% and the mean dose to the lungs on the same side of cancer decreased by 7.45%. Conclusions The model allowing gantry acceleration allows the treatment time to be significantly shortened and the treatment efficiency improved. Although this model had the shortcomings such as affecting the conformity and uniformity of target areas to a certain extent and increasing the doses to some OARs, clinical requirements for dosimetry were still met. Therefore, it is recommended to use the model allowing gantry acceleration in the Pinnacle planning system.