Second Round of Gamma Knife Radiotherapy Proves Safe and Durable for Recurring Brain Tumors

When a brain tumor comes back after radiation therapy, patients and their doctors face one of the most difficult dilemmas in neuro-oncology: how to attack the recurring growth without causing catastrophic damage to brain tissue that has already absorbed a near-maximal dose of radiation. A new study from the Odette Cancer Centre at Sunnybrook Health Sciences Centre in Toronto, published in the Journal of Neuro-Oncology, suggests that a carefully engineered second course of Gamma Knife radiotherapy can be delivered safely and effectively, achieving durable tumor control in patients whose non-glial brain tumors had returned despite prior definitive treatment.

The research, led by Cristian Udovicich and senior author Arjun Sahgal, focused on a technique the team calls salvage conventionally fractionated Gamma Knife stereotactic radiotherapy, abbreviated SFGK. Unlike single-session stereotactic radiosurgery, which delivers one concentrated blast of radiation, conventional fractionation spreads the treatment over many small daily doses, in this case most often 50.4 Gy delivered in 28 fractions. The approach exploits a fundamental principle of radiobiology: dividing a dose into smaller increments spares normal tissue far more than it spares the tumor, because healthy cells are better at repairing sublethal radiation damage between treatments than many tumor cells are.

Between 2019 and 2024, twenty-six consecutive patients harboring forty-four recurrent tumors underwent the salvage procedure. The overwhelming majority of these lesions, thirty-four in total or roughly three-quarters of the cohort, were meningiomas, the tumors that arise from the meninges, the protective membranes enveloping the brain and spinal cord. Most of these meningiomas were not benign; twenty-eight of the thirty-four were classified as World Health Organization Grade 2, an atypical form known for its stubborn tendency to recur even after surgery and radiation. The remaining patients carried other primary non-glial tumors, a category that excludes the gliomas and glioblastomas that originate from brain support cells and dominate much of the neuro-oncology literature.

What makes the study remarkable is the sheer amount of radiation these patients had already received. The median interval between the original radiotherapy course and the salvage treatment was 50.4 months, meaning most patients had enjoyed roughly four years of disease control before their tumors returned. Once SFGK was delivered, the median cumulative prescription dose, calculated using the EQD2 metric, which converts any radiation schedule into the biologically equivalent dose of 2 Gy per fraction, reached a staggering 102.7 Gy for patients who had undergone one prior course. For context, that figure approaches the tolerance limits of normal brain tissue, a territory where most radiation oncologists fear to tread.

The investigators were acutely aware of this danger, and the study’s dosimetry reflects a deliberate balancing act. The median EQD2 dose accumulated by normal brain tissue was 99.2 Gy, uncomfortably close to the tumor dose itself. This proximity underscores why conventional fractionation was chosen: by stretching 50.4 Gy across 28 sessions, the technique spreads out the biological burden on healthy tissue and allows gradual repair, while the precision of the Gamma Knife Icon platform, which integrates cone-beam CT imaging for frameless stereotactic guidance, ensures the radiation conforms tightly to each lesion. Earlier work by the same group, published in the Journal of Neurosurgery in 2023, had reported the first evidence that fractionated Gamma Knife reirradiation was feasible; the new study extends that signal with a larger cohort and formal survival statistics.

The results exceeded what many in the field would have predicted for such heavily irradiated tissue. Local progression-free survival, the study’s primary endpoint, stood at 91.0 percent at twelve months and 75.1 percent at twenty-four months across all patients. For the meningioma subgroup specifically, the corresponding figures were 90.6 percent and 74.1 percent. Overall survival was even more striking: 96.2 percent of patients were alive at one year and 83.2 percent at two years. In a population whose tumors had already defied surgery and a full course of radiation, these numbers represent a meaningful extension of disease control, particularly for atypical meningiomas, which historically carry poor outcomes at recurrence.

Safety data, often the Achilles heel of reirradiation studies, proved encouraging. Only two patients, or 6.9 percent of the cohort, developed Grade 3 radionecrosis, the dreaded condition in which irradiated brain tissue dies and swells, sometimes requiring surgery or corticosteroid therapy. A single patient, 3.4 percent, experienced Grade 3 progressive intracranial hemorrhage. Crucially, no Grade 4 or Grade 5 events, the most severe toxicity categories, were observed at all. With a median follow-up of 18.1 months, the authors acknowledge that late toxicities can take years to fully declare themselves, but the early safety profile appears acceptable given the extraordinarily high cumulative doses involved.

The study arrives at a moment when options for recurrent meningioma are desperately limited. Surgery at recurrence is often incomplete because these tumors adhere to critical vessels and nerves, and drug development has struggled; even recent trials of radioligand therapies such as lutetium-177 DOTATATE, tested prospectively in surgery- and radiation-refractory meningioma, remain experimental. Alternative reirradiation approaches using proton beams or carbon ions have shown promise but demand infrastructure unavailable to most patients. Fractionated Gamma Knife, by contrast, leverages equipment already installed in major cancer centers worldwide, making SFGK a potentially scalable salvage strategy.

The Toronto team’s work also fits into a broader movement in radiation oncology to formalize the once-forbidden practice of reirradiation. Recent prospective studies have established conventionally fractionated dose constraints for reirradiating primary brain tumors in adults, and the American Radium Society has published appropriate use criteria for retreatment in head and neck cancers. The Sunnybrook experience now provides some of the strongest evidence yet that primary brain tumors, specifically, can tolerate a second radical course when delivered with stereotactic precision and fractionation. A related report in 2025 documented even a third course of radical-intent conformal radiation in selected patients, suggesting the ceiling on cumulative dose may be higher than traditionally assumed when treatments are spaced and planned carefully.

For the patients whose atypical meningiomas had returned after years of remission, the study offers something that has long been in short supply: a well-tolerated option that meaningfully delays progression. The authors caution that their findings come from a retrospective single-institution series of twenty-six patients, and that longer follow-up will be needed to confirm durability and capture late toxicity. Yet the central conclusion stands on firm ground within those limits. Delivered in conventionally fractionated form on a modern frameless Gamma Knife platform, salvage reirradiation is feasible, achieves durable local control, and produces few serious adverse events, even when cumulative doses approach one hundred grays. For a field where recurrent, previously irradiated tumors have often meant palliative care alone, that is a result worth celebrating.

Subject of Research: Salvage fractionated Gamma Knife reirradiation for recurrent primary non-glial brain tumors

Article Title: Reirradiation outcomes following salvage conventionally fractionated Gamma Knife stereotactic radiotherapy (SFGK) to recurrent primary non-glial brain tumors

Article References: Udovicich, C., Tseng, C.-L., Detsky, J., Chen, H., Dinakaran, D., Soliman, H., Zeng, K. L., Ruschin, M., Yeboah, C., Holden, L., Atenafu, E. G., & Sahgal, A. (2026). Reirradiation outcomes following salvage conventionally fractionated Gamma Knife stereotactic radiotherapy (SFGK) to recurrent primary non-glial brain tumors. Journal of Neuro-Oncology, 179(3), Article 88. https://doi.org/10.1007/s11060-026-05757-3

Image Credits: AI Generated

DOI: 10.1007/s11060-026-05757-3

Keywords: Gamma Knife, reirradiation, meningioma, brain tumors, stereotactic radiotherapy, radiation necrosis, local control, radionecrosis, WHO Grade 2 meningioma, fractionated stereotactic radiotherapy, salvage therapy, neuro-oncology