Ohtakara Kazuhiro, Suzuki Kojiro
Department of Radiation Oncology, Kainan Hospital Aichi Prefectural Welfare Federation of Agricultural Cooperatives, Yatomi, JPN.
Department of Radiology, Aichi Medical University, Nagakute, JPN.
Cureus. 2025 Aug 4;17(8):e89380. doi: 10.7759/cureus.89380. eCollection 2025 Aug.
Background This study was conducted to examine the effects of moving the isocenter (IC) position from the lesion to the center of the brain on stereotactic radiosurgery (SRS) planning with volumetric-modulated arcs (VMA) using the High-Definition Dynamic Radiosurgery (HDRS) platform, a combination of the Agility multileaf collimator (MLC) (Elekta AB, Stockholm, Sweden) and the Monaco planning system (Elekta AB), for single brain metastases (BMs). Methodology The study subject included 36 clinical BMs with the gross tumor volume (GTV) ranging from 0.04 to 48.09 cc (median 7.91 cc). Two VMA plans were prepared for each GTV under identical conditions except for the location of the IC as follows: the center of each GTV (IC_GTV) vs. the center of the brain (IC_Brain). The same prescription dose was uniformly assigned to each GTV , the minimum dose to a GTV minus 0.01 cc ( ), for GTV >0.20 cc and for GTV ≤0.20 cc. Results The GTV values on the dose-volume histograms (DVHs) were different from the same contoured volumes, and the differences were considerably different between the IC_GTV and the IC_Brain, ranging from -0.07 to 0.14 cc. The inter-IC distances significantly decreased as the depths of the GTV increased. The total calculation times (tCT) and total monitor units (MU) per fraction were significantly longer and higher in the IC_Brain than in the IC_GTV, respectively. The MU differences significantly increased as the IC distances increased. The dose 2 mm inside the GTV boundary was significantly higher in the IC_Brain than the IC_GTV, while there were no significant differences in the other metrics relevant to the dose conformity and gradients outside and inside the GTV boundary. The lack of significant differences in the dose distributions was mainly attributed to some of the leaf widths of essentially <5 mm, variable by the dynamic involvement of diaphragms in the segment formation, and the different combinations of MLC angles with 0º, 45º, and 90º. Conclusions HDRS with VMA created similar dose distributions for SRS of single BMs, irrespective of the IC position, except for the steepness of dose increase just inside the GTV boundary. However, moving the IC from the lesion to the center of the brain significantly increased the tCT and total MU per fraction and was associated with a substantial change in the GTV value on the DVH. Positioning the IC to the center of each lesion is generally recommended for VMA-based HDRS of single BMs.
背景 本研究旨在使用高清动态放射外科（HDRS）平台（即敏捷多叶准直器（MLC）（瑞典斯德哥尔摩医科达公司）与医科达 Monaco 计划系统的组合），针对单发性脑转移瘤（BM），研究将等中心（IC）位置从病变处移至脑中心对容积调强弧形放疗（VMA）立体定向放射外科（SRS）计划的影响。
方法 研究对象包括 36 例临床 BM，其大体肿瘤体积（GTV）范围为 0.04 至 48.09 立方厘米（中位数 7.91 立方厘米）。除 IC 位置外，在相同条件下为每个 GTV 制定了两个 VMA 计划：每个 GTV 的中心（IC_GTV）与脑中心（IC_Brain）。相同的处方剂量被均匀分配给每个 GTV，对于 GTV>0.20 立方厘米，为 GTV 减去 0.01 立方厘米的最小剂量（ ），对于 GTV≤0.20 立方厘米，为 。
结果 剂量体积直方图（DVH）上的 GTV 值与相同轮廓体积不同，且 IC_GTV 和 IC_Brain 之间的差异显著不同，范围为 -0.07 至 0.14 立方厘米。随着 GTV 的深度增加，IC 之间的距离显著减小。IC_Brain 中每次分割的总计算时间（tCT）和总监测单位（MU）分别显著长于和高于 IC_GTV。随着 IC 距离增加，MU 差异显著增大。GTV 边界内 2 毫米处的剂量在 IC_Brain 中显著高于 IC_GTV，而在 GTV 边界内外与剂量适形性和梯度相关的其他指标上没有显著差异。剂量分布缺乏显著差异主要归因于一些基本宽度<5 毫米的叶片宽度，其因膈肌在段形成中的动态参与而变化，以及 MLC 角度 0°、45°和 90°的不同组合。
结论 对于单发性 BM 的 SRS，使用 VMA 的 HDRS 产生了相似的剂量分布，无论 IC 位置如何，除了 GTV 边界内剂量增加的陡度。然而，将 IC 从病变处移至脑中心显著增加了每次分割的 tCT 和总 MU，并与 DVH 上 GTV 值的显著变化相关。对于基于 VMA 的单发性 BM 的 HDRS，一般建议将 IC 定位在每个病变的中心。
