单一等中心多靶技术已成为治疗多发性脑转移的常用技术。我们实施了一种获取非均匀边界的 SIMT 技术的方法。在本研究中，我们进一步提出了一种确定等中心位置的方法，使得总扩展边界体积最小化。基于统计模型，建立了非均匀边界与距离 d （从等中心到目标点）、设定不确定性和显著性水平之间的关系。由于旋转误差的存在，边界体积与等中心位置之间存在非线性关系。通过数值模拟，我们研究了最佳等中心位置与平移误差、旋转误差和目标大小之间的关系。为了快速找到最佳等中心位置，使用了自适应模拟退火 (ASA) 算法。此方法已应用于 Pinnacle3 治疗计划系统，并与几何中心 (COG)、体积中心 (COV) 和表面中心 (COS) 的等中心点进行比较。选取了治疗 SIMT 技术的十名多发性脑转移靶点患者进行评估。当肿瘤大小相同时，ASA 和数值模拟得到的最佳等中心与 COG、COV 和 COS 重合。当肿瘤大小不同时，最佳等中心靠近大肿瘤。对于几乎所有病例，COS 点的位置比 COV 点更接近最佳点。此外，在某些情况下，COS 点可以近似选择为最佳点。ASA 算法可以将计算时间从几个小时减少到几十秒，适用于三个或更多肿瘤的情况。使用多发性脑转移靶点，获得了一系列不同肿瘤数、肿瘤大小和分离距离的体积差异和计算时间。与 COG 等中心点的边界体积相比，最佳点的边界体积可以减少高达 27.7%。针对不同肿瘤之间进行最佳治疗等中心选择可以减少总边界体积。ASA 算法可以显著提高寻找最佳等中心的速度。此方法可用于临床等中心选择，并对附近正常组织的保护具有益处。© 2022 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, LLC on behalf of The American Association of Physicists in Medicine.

The single isocenter for multiple-target (SIMT) technique has become a popular treatment technique for multiple brain metastases. We have implemented a method to obtain a nonuniform margin for SIMT technique. In this study, we further propose a method to determine the isocenter position so that the total expanded margin volume is minimal.Based on a statistical model, the relationship between nonuniform margin and the distance d (from isocenter to target point), setup uncertainties, and significance level was established. Due to the existence of rotational error, there is a nonlinear relationship between the margin volume and the isocenter position. Using numerical simulation, we study the relationship between optimal isocenter position and translational error, rotational error, and target size. In order to find the optimal isocenter position quickly, adaptive simulated annealing (ASA) algorithm was used. This method was implemented in the Pinnacle3 treatment planning system and compared with isocenter at center-of-geometric (COG), center-of-volume (COV), and center-of-surface (COS). Ten patients with multiple brain metastasis targets treated with the SIMT technique was selected for evaluation.When the size of tumors is equal, the optimal isocenter obtained by ASA and numerical simulation coincides with COG, COV, and COS. When the size of tumors is different, the optimal isocenter is close to the large tumor. The position of COS point is closer to the optimal point than the COV point for nearly all cases. Moreover, in some cases the COS point can be approximately selected as the optimal point. The ASA algorithm can reduce the calculating time from several hours to tens of seconds for three or more tumors. Using multiple brain metastases targets, a series of volume difference and calculating time were obtained for various tumor number, tumor size, and separation distances. Compared with the margin volume with isocenter at COG, the margin volume for optimal point can be reduced by up to 27.7%.Optimal treatment isocenter selection of multiple targets with large differences could reduce the total margin volume. ASA algorithm can significantly improve the speed of finding the optimal isocenter. This method can be used for clinical isocenter selection and is useful for the protection of normal tissue nearby.© 2022 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, LLC on behalf of The American Association of Physicists in Medicine.