Dosimetric parameters associated with the long-term oncological outcomes of Gamma Knife surgery for sellar and parasellar tumors in pediatric patients

OBJECTIVE The authors aimed to investigate the dosimetric parameter and the minimally required dose associated with long-term control of sellar and parasellar tumors after Gamma Knife surgery (GKS) in children. METHODS A retrospective analysis was performed on pediatric patients younger than 19 years of age who were diagnosed with sellar and parasellar tumors and received GKS at the authors’ institution from 1998 to 2019. Cox proportional hazards regression analyses were used to investigate the dosimetric parameters associated with treatment outcome. The Kaplan-Meier method was used to analyze tumor control rates after GKS. RESULTS Overall, 37 patients with 40 sellar and parasellar tumors, including 22 craniopharyngiomas and 12 pituitary adenomas, had a mean follow-up of 85.8 months. The gross target volume was 0.05 cm3 to 15.28 cm3, and the mean marginal dose was 15.8 Gy (range 9.6–30.0 Gy). Ten patients experienced treatment failure at a mean of 28.0 ± 26.7 months. The actuarial 5- and 10-year tumor control rates were 79.0% and 69.8%, respectively. D98% was an independent predictive factor of tumor control (HR 0.846 [95% CI 0.749–0.956], p = 0.007), with a cutoff value of 11.5 Gy for the entire cohort and 10 Gy for the craniopharyngioma group. Visual deterioration occurred in 2 patients with the maximum point dose of 10.1 Gy and 10.6 Gy to the optic apparatus. CONCLUSIONS In pediatric patients, D98% was a reliable index of the minimum required dose for long-term control of sellar and parasellar tumors after GKS. The optimal D98% value for each tumor diagnosis needs to be elucidated in the future.

RADI-06. Gamma knife surgery for brain stem metastases

Introduction Gamma Knife Surgery (GKS) is widely used for treatment of brainstem metastases (BSMs) with or without whole bran radiation therapy (WBRT). We hypothesized that BSMs treated with GKS using lower doses and omitting WBRT result in acceptable tumor control rates and low complication rates. Methods A retrospective single center study was performed to investigate the outcome following GKS of BSMs. All 33 patients with follow-up information treated with GKS for 39 metastases located in the cerebral peduncle, midbrain, pons or medulla oblongata were included in the study. The median treatment dose, defined as the lowest dose to 95% of the tumor volume, was 18 Gy. The tumor control rate as well as the survival time were related to a number of patients, tumor and treatment parameters. Results The local tumor control rate was 100% at one year and 89% at five years, and the overall median survival was 17 months. A good performance status and a treatable extracranial disease were favorably related to survival time. Two complications were observed, one lethal hemorrhage at the day of the treatment and one transient complication three months following GKS, resulting in a 6% complication rate at five years. Four of the 10 patient with symptomatic BSM improved clinically after GKS, while six remained unchanged. Conclusions High local control and a low complication rates can be achieved using GKS for BSMs using lower doses as compared to brain metastases in other locations.

RADI-21. Feasibility of Gamma Knife Surgery for patients with 20 or more brain metastases

Background The current standard-of-care treatment for brain metastases (BM)≥20 is Whole Brain Radiotherapy (WBRT), which can cause neurocognitive decline detrimental to patients’ quality of life, especially if their functional status is good on presentation. The benefits of Gamma Knife Surgery (GKS) have been shown for BM≤10, but there is no consensus on the upper limit where GKS is no longer beneficial. We hypothesize that selected patients with ≥20 BM may benefit by replacing WBRT with GKS to preserve neurocognition without compromising intracerebral tumor control and overall survival, with additional treatments as needed. Methodology This is retrospective analysis of 31 patients with ≥20 BM who underwent single-session GKS between 2016–2021. Twenty-two patients had ECOG of 0 at the time of GKS. Median number of BM at GKS was 30 (20–79) with median total tumour volume 4cm3 (2–28 cm3). Median marginal dose was 20Gy (10-25Gy). Results Median overall survival following GKS was 14-months (95%CI 4-24months), justifying GKS in this population. 11/12 patients that died succumbed due to extracranial disease, while 1 patient, who was treated with WBRT before GKS, succumbed to intracranial tumor progression. Local tumor control achieved was achieved for 63% of patients at 2-years and distal tumor control in 24% of patients at 1.5-years without additional radiation treatment. Salvage GKS was given in seven patients and salvage WBRT in three. One local recurrence was surgically resected. Systemic treatment given to most patients probably contributed to intracranial tumor control. No patients developed significant neurocognitive deficits attributable to GKS during the follow-up period of median 7-months (Q1-Q3: 3-12months). Conclusion Most patients treated with GKS for ≥20 BM have sufficient survival time to benefit from the treatment. Local and distal recurrences can be managed with systemic treatment, salvage GKS, or WBRT, resulting in intracerebral tumor control in vast majority of cases.

Dosimetric Parameters Associated with the Long-Term Oncologic Outcomes of Gamma Knife Surgery for Sellar and Parasellar Tumors in Pediatric Patients

Purpose We aimed to investigate the dosimetric parameter and the minimally required dose associated with long-term control of sellar and parasellar tumors after gamma knife surgery (GKS) in children. Methods A retrospective analysis was performed on pediatric patients under the age of 19 who were diagnosed with sellar and parasellar tumors and received GKS in our institution from 1998 to 2019. Cox proportional hazards regression analyses were used to investigate the dosimetric parameters associated with treatment outcome. The Kaplan-Meier method was used to analyze tumor control rates after GKS. Results Thirty-seven patients with 40 sellar and parasellar tumors, including 22 craniopharyngiomas and 12 pituitary adenomas, were followed up for a mean of 85.8 months. The gross target volume was 0.05 − 15.28 cm3, and the mean marginal dose was 15.8 Gy (range, 9.6–30.0 Gy). Ten patients experienced treatment failure at 28.0 ± 26.7 months. The actuarial 5- and 10-year tumor control rates were 79.0% and 69.8%, respectively. D98% was an independent predictive factor of tumor control (p = 0.007, hazard ratio 0.846, 95% confidence interval 0.749–0.956), with cutoff values of 11.5 Gy in the entire cohort and 10 Gy in the craniopharyngioma group. Visual deterioration occurred in two patients with the maximum point dose of 10.1 Gy and 10.6 Gy to the optic apparatus. Conclusion D98% is a reliable index of the minimum required dose for long-term control of sellar and parasellar tumors after GKS. The optimal D98% value for each diagnosis needs to be elucidated in the future.

Radiosurgery-Based AVM Scale Is Proposed for Combined Embolization and Gamma Knife Surgery for Brain Arteriovenous Malformations

Background and purpose: To evaluate whether a radiosurgery-based arteriovenous malformation (AVM) scale (RBAS) could be used to predict obliteration of brain arteriovenous malformations (bAVMs) supposed for combined endovascular embolization (EMB) and gamma knife surgery (GKS) treatment.Methods: bAVM patients who underwent GKS with or without previous EMB from January 2011 to December 2016 at our institution were retrospectively reviewed. The patients were categorized into a combined treatment group and a GKS group. A 1:1 propensity score matching (PSM) was used to match the two groups. Pre-EMB and pre-GKS RBAS were assessed for every patient. Multivariate analysis was performed to find factors associated with complete obliteration in the combined treatment group. Survival analysis based on sub-groups according to RBAS was performed to compare obliteration rate and find cutoffs for appropriate treatment modalities.Results: A total of 96 patients were involved, and each group comprised 48 patients. There was no difference between the two groups in terms of obliteration rate (75.0 vs. 83.3%, p = 0.174). Pre-EMB RBAS (p = 0.010) and the number of feeding arteries (p = 0.014) were independent factors associated with obliteration rate in the combined treatment group. For the combined treatment patients, sub-group analysis according to pre-EMB RBAS (score <1.0, 1.0–1.5, and >1.5) showed statistical difference in obliteration rate (p = 0.002). Sub-group analysis according to RBAS between the two groups showed that the obliteration rate of the GKS group is significantly higher than the combined group when RBAS >1.5 (47.4 vs. 66.7%, p = 0.036).Conclusions: The RBAS is proposed to be efficient in predicting obliteration of bAVMs supposed to receive combined EMB and GKS treatment. Patients with RBAS >1.5 are inclined to be more suitable for GKS instead of the combined treatment.

Gamma Knife Radiosurgery of Distal Aneurysm: A Case Series

A series of 3 patients (35–60 years old) with bleeding distal aneurysm not associated with AVM who underwent radiosurgery by gamma knife are reported. One isocentre centralized over the aneurysm was used; peripheral dose 24–28.8 Gy was applied. Control angiography 20–36 months after gamma knife surgery (GKS) demonstrated obliteration of both the aneurysm and the feeding artery, without deterioration of the neurological symptoms. Our case series implies that GKS might serve as a safe mini-invasive technique in the treatment of selected distal aneurysms.