Objective Gamma knife (GK) staged stereotactic radiosurgery (Staged-SRS) has become an effective treatment option for large brain metastases (BMs); however, it has been challenging to evaluate the total dose because of tumor shrinkage between two staged sessions. This study aims to evaluate total biological effective dose (BED) in Staged-SRS, and to compare the BED with those in single-fraction SRS (SF-SRS) and hypo-fractionated SRS (HF-SRS). Methods Patients treated with GK Staged-SRS at a single institution were retrospectively included. The dose delivered in two sessions of Staged-SRS was summed using the deformable image registration. Each patient was replanned for SF-SRS and HF-SRS. The total BEDs were computed using the linear-quadratic model. Tumor BED98% and brain V84Gy2, equivalent to V12Gy in SF-SRS, were compared between SF-SRS, HF-SRS, and Staged-SRS plans with the Wilcoxon test. Results Twelve patients with 24 BMs treated with GK Staged-SRS were identified. We observed significant differences (p < 0.05) in tumor BED98% but comparable brain V84Gy2 (p = 0.677) between the Staged-SRS and SF-SRS plans. No dosimetric advantages of Staged-SRS over HF-SRS were observed. Tumor BED98% in the HF-SRS plans were significantly higher than those in the Staged-SRS plans (p < 0.05). Despite the larger PTVs, brain V84Gy2 in the HF-SRS plans remained lower (p < 0.05). Conclusion We presented an approach to calculate the composite BEDs delivered to both tumor and normal brain tissue in Staged-SRS. Compared to SF-SRS, Staged-SRS delivers a higher dose to tumor but maintains a comparable dose to normal brain tissue. Our results did not show any dosimetric advantages of Staged-SRS over HF-SRS.

中文翻译：

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伽玛刀分期立体定向放射外科治疗大脑转移瘤的生物有效剂量评估。

目的伽玛刀（GK）分期立体定向放射外科（Staged-SRS）已成为大脑转移瘤（BMs）的有效治疗选择；然而，由于两个阶段之间的肿瘤缩小，评估总剂量一直具有挑战性。本研究旨在评估分期 SRS 中的总生物有效剂量 (BED)，并将 BED 与单次分割 SRS (SF-SRS) 和大分割 SRS (HF-SRS) 中的 BED 进行比较。方法 回顾性纳入在单一机构接受 GK Staged-SRS 治疗的患者。使用可变形图像配准对两次阶段性 SRS 的剂量进行求和。每位患者都重新计划了 SF-SRS 和 HF-SRS。使用线性二次模型计算总 BED。在 SF-SRS、HF-SRS、和带有 Wilcoxon 测试的 Staged-SRS 计划。结果 确定了 12 名接受 GK Staged-SRS 治疗的 24 BMs 患者。我们观察到分期-SRS 和 SF-SRS 计划之间肿瘤 BED98% 的显着差异 (p < 0.05) 但脑 V84Gy2 (p = 0.677) 相当。没有观察到 Staged-SRS 优于 HF-SRS 的剂量学优势。HF-SRS 计划中的肿瘤 BED98% 显着高于 Staged-SRS 计划（p < 0.05）。尽管 PTV 较大，HF-SRS 计划中的脑 V84Gy2 仍然较低（p < 0.05）。结论 我们提出了一种计算在 Staged-SRS 中递送到肿瘤和正常脑组织的复合 BED 的方法。与 SF-SRS 相比，Staged-SRS 向肿瘤提供更高的剂量，但保持与正常脑组织相当的剂量。