联影可旋转540°机架直线加速器在容积调强放疗计划中的效率优势分析

Analysis of efficiency advantage of the United Imaging Healthcare (UIH) linac 540° gantry in volume intensity-modulated radiotherapy plan

背景与目的:由于传统加速器机架无法跨过180°,对于肿瘤靠近背侧的患者,常采用拼接弧的方式进行放疗计划设计,虽能提高肿瘤控制率,但会增加机架空转时间,同时也会增加机架与患者碰撞的风险。对比分析联影可旋转540°加速器与传统360°加速器(不跨越180°)在容积弧形旋转调强放疗(volumetric-modulated arc therapy,VMAT)计划执行时的潜在优势。方法:按照不同弧长和任意起始角度,随机生成100个弧,按照机架运动轨迹的特性分别分为A、B两组,其中A组计划(540°机架)为可以跨越180°的弧;B组计划(360°机架)为两段位于180°两侧,由总弧长等于A组的两段弧拼接而成。通过轨迹模拟软件,采用double S velocity模型描述转动轨迹,进行复位情况下的执行效率模拟,并结合临床实际病例对A、B两组进行效率优势分析。结果:A组和B组总执行时间、出束时间接近,差异主要来自机器空转。结合临床实际场景,考虑复位,空转时间与双弧计划比例成正比,节省时间最大值为全双弧计划,节省约32 min。对于临床实际病例,全满弧计划执行时间最多可缩短约85 min。结论:540°机架在执行VMAT计划时,特别是对偏离人体中心的计划,在满足临床剂量分布的同时,可以节省机架空转和复位时间,提高治疗效率,并且能有效地避免机架与患者碰撞的风险。

Background and purpose: For off-center patients, split arcs are used for radiotherapy plan to increase the tumor control rate, as the traditional linear accelerator(linac) gantry cannot span 180°. This method increases the idling time and the risk of collision between the gantry and the patient. The purpose of this study was to compare and analyze the potential advantages in volumetric-modulated arc therapy(VMAT) plans between the United Imaging Healthcare(UIH) linac 540° gantry and the traditional 360° gantry. Methods: In this study, 100 arc plans were randomly generated according to different arc lengths and arbitrary starting points, and they were divided into two groups. Group A included arcs that could span 180°, and group B plan consisted of two arcs on both sides of 180° with total arc length equal to group A. By using the trajectory simulation software, the double S velocity model was used to describe the rotational trajectory, and the execution efficiency simulation was carried out considering the reset time. In addition, the efficiency advantages of group A and B were also analyzed based on 10 actual clinical cases. Results: Comparing the execution time of group A and B, the difference mainly came from the idling time of gantry without considering the reset time. For clinical routine, the idling time was proportional to the proportion of the double arc plan. The maximum saving time was the full double arc plan, saving about 32 minutes. The maximum execution time of full arc plan could be reduced by about 85 minutes in clinical situation. Conclusion: For VMAT plan in which tumors are deviated from the center of patient, the UIH machine can save the idling time of the gantry and improve efficiency while meet the clinical dose distribution. In addition, it can effectively avoid the risk of collision between the gantry and the patient.