1Department of Radiation Oncology, Sunnybrook Health Sciences Centre.
2Division of Neurosurgery, St. Michael's Hospital.
J Neurosurg. 2022 Aug 19;138(3):674-682. doi: 10.3171/2022.6.JNS22998. Print 2023 Mar 1.
With the incorporation of real-time image guidance on the Gamma Knife system allowing for mask-based immobilization (Gamma Knife Icon [GKI]), conventionally fully fractionated (1.8-3.0 Gy/day) GKI radiation can now be delivered to take advantage of an inherently minimal margin for delivery uncertainty, sharp dose falloff, and inhomogeneous dose distribution. This case series details the authors' preliminary experience in re-irradiating 7 complex primary intracranial tumors, which were considered to have been previously maximally radiated and situated adjacent to critical organs at risk.
The authors retrospectively reviewed all patients who received fractionated re-irradiation using GKI at the Sunnybrook Health Sciences Centre, University of Toronto, Ontario, Canada, between 2016 and 2021. Patients with brain metastases, and those who received radiotherapy courses in 5 or fewer fractions, were excluded. All radiotherapy doses were converted to the equivalent total dose in 2-Gy fractions (EQD2), with the assumption of an α/β ratio of 2 for late normal tissue toxicity and 10 for the tumor.
A total of 7 patients were included in this case series. Three patients had recurrent meningiomas, as well as 1 patient each with ependymoma, intracranial sarcoma, pituitary macroadenoma, and papillary pineal tumor. Six patients had undergone prior linear accelerator-based conventional fractionated radiotherapy and 1 patient had undergone prior proton therapy. Patients were re-irradiated with a median (range) total dose of 50.4 (30-63.4) Gy delivered in a median (range) of 28 (10-38) fractions with GKI. The median (range) target volume was 6.58 (0.2-46.3) cm3. The median (range) cumulative mean EQD2 administered to the tumor was 121.1 (107.9-181.3) Gy, and the median (range) maximum point EQD2 administered to the brainstem, optic nerves, and optic chiasm were 91.6 (74.0-111.5) Gy, 58.9 (6.3-102.9) Gy, and 59.9 (36.7-127.3) Gy, respectively. At a median (range) follow-up of 15 (6-42) months, 6 of 7 patients were alive with 4 having locally controlled disease. Only 3 patients experienced treatment-related toxicities, which were self-limited.
Fractionated radiotherapy using GKI may be a safe and effective method for the re-irradiation of complex progressive primary intracranial tumors, where the aim is to minimize the potential for serious late effects.
伽玛刀系统整合实时图像引导，实现基于面罩的固定（伽玛刀 Icon [GKI]），常规的完全分割（1.8-3.0 Gy/天）GKI 辐射现在可以用于利用 Delivery Uncertainty、Sharp Dose Falloff 和不均匀剂量分布的固有最小边缘。本病例系列详细介绍了作者在再照射 7 个复杂原发性颅内肿瘤方面的初步经验，这些肿瘤被认为先前已接受最大程度的放射治疗，并且位于危及生命的关键器官附近。
作者回顾性分析了 2016 年至 2021 年期间在加拿大安大略省多伦多大学桑尼布鲁克健康科学中心接受分次再照射的所有患者。排除脑转移患者和接受 5 次或更少放射治疗的患者。所有放射治疗剂量均转换为 2 Gy 等效总剂量（EQD2），假设晚期正常组织毒性的 α/β 比为 2，肿瘤为 10。
本病例系列共纳入 7 例患者。3 例为复发性脑膜瘤，1 例为室管膜瘤、颅内肉瘤、垂体大腺瘤和乳头状松果体瘤。6 例患者曾接受过基于线性加速器的常规分割放射治疗，1 例患者曾接受过质子治疗。患者接受 GKI 再照射，中位（范围）总剂量为 50.4（30-63.4）Gy，中位（范围）分割次数为 28（10-38）次。中位（范围）靶体积为 6.58（0.2-46.3）cm3。中位（范围）肿瘤累积平均 EQD2 剂量为 121.1（107.9-181.3）Gy，中位（范围）脑干、视神经和视交叉最大点 EQD2 剂量分别为 91.6（74.0-111.5）Gy、58.9（6.3-102.9）Gy 和 59.9（36.7-127.3）Gy。中位（范围）随访时间为 15（6-42）个月，7 例患者中有 6 例存活，4 例局部疾病得到控制。仅 3 例患者出现与治疗相关的毒性，为自限性。
使用 GKI 的分次放射治疗可能是一种安全有效的方法，用于再照射复杂的进行性原发性颅内肿瘤，其目的是尽量减少严重晚期效应的潜在风险。
