Gamma Knife Radiosurgery for the Management of More Than 15 Cerebral Metastases

Assessing the impact of distortion correction on Gamma Knife radiosurgery for multiple metastasis: Volumetric and dosimetric analysis

Introduction

Magnetic resonance imaging (MRI) is a robust neuroimaging technique and is the preferred method for stereotactic radiosurgery (SRS) planning. However, MRI data always contain distortions caused by hardware and patient factors.

Research question

Can these distortions potentially compromise the effectiveness and safety of SRS treatments?

Material and methods

Twenty-six MR datasets with multiple metastatic brain tumors (METs) used for Gamma Knife radiosurgery (GKRS) were retrospectively evaluated. A commercially available software was used for distortion correction. Geometrical agreement between corrected and uncorrected tumor volumes was evaluated using MacDonald criteria, Euclidian distance, and Dice similarity coefficient (DSC). SRS plans were generated using uncorrected tumor volumes, which were assessed to determine their coverage of the corrected tumor volumes.

Results

The median target volume was 0.38 cm3 (range,0.01-12.38 cm3). A maximum displacement of METs of up to 2.87 mm and a median displacement of 0.55 mm (range,0.1-2.87 mm) were noted. The median DSC between uncorrected and corrected MRI was 0.92, and the most concerning case had a DSC of 0.46. Although all plans met the optimization criterion of at least 98% of the uncorrected tumor volume (median 99.55%, range 98.1-100%) receiving at least 100% of the prescription dose, the percent of the corrected tumor volume receiving the total prescription dose was a median of 95.45% (range,23.1-99.5%).

Discussion and conclusion

MRI distortion, though visually subtle, has significant implications for SRS planning. Regular utilization of corrected MRI is recommended for SRS planning as distortion is sometimes enough to cause a volumetric miss of SRS targets.

Overall survival following stereotactic radiosurgery for ten or more brain metastases: a systematic review and meta-analysis

BACKGROUND

Brain metastases are the most common intracranial tumours. Variation exists in the use of stereotactic radiosurgery for patients with 10 or more brain metastases. Concerns include an increasing number of brain metastases being associated with poor survival, the lack of prospective, randomised data and an increased risk of toxicity.

METHODS

We performed a systematic review and meta-analysis to assess overall survival of patients with ten or more brain metastases treated with stereotactic radiosurgery as primary therapy. The search strings were applied to MEDLINE, Embase and the Cochrane Central Register of Controlled Trials (CENTRAL). Log hazard ratios and standard errors were estimated from each included study. A random-effects meta-analysis using the DerSimonian and Laird method was applied using the derived log hazard ratios and standard errors on studies which included a control group.

RESULTS

15 studies were included for systematic review. 12 studies were used for pooled analysis for overall survival at set time points, with a predicted 12 month survival of 20-40%. The random-effects meta-analysis in five studies of overall survival comparing ten or greater metastases against control showed statistically worse overall survival in the 10 + metastases group (1.10, 95% confidence interval 1.03-1.18, p-value = < 0.01, I2 = 6%). A funnel plot showed no evidence of bias. There was insufficient information for a meta-analysis of toxicity.

DISCUSSION

Overall survival outcomes of patients with ten or more brain metastases treated with SRS is acceptable and should not be a deterrent for its use. There is a lack of prospective data and insufficient real-world data to draw conclusions on toxicity.

PROSPERO ID

CRD42021246115.

Single-Session Gamma Knife Radiosurgery for Patients With 20 or More Brain Metastases

BACKGROUND

Stereotactic radiosurgery (SRS) is a widely accepted treatment modality for brain metastases. The role of SRS in patients with higher numbers of metastases remains controversial.

OBJECTIVES

To define outcomes in patients with ≥20 brain metastases managed using single-session SRS.

METHODS

This single-institution retrospective cohort study studied 75 patients (26 non-small-cell lung cancer, 21 small-cell lung cancer, 14 breast cancer, and 14 melanoma) undergoing single-session SRS. The median number of tumors per patient was 24, and the median cumulative tumor volume was 3.70 cc. The median margin dose prescribed to each individual tumor was 16 Gy. The median integral cranial dose was 5492 mJ. The median beam on time was 160 minutes. Univariate and multivariate analyses were performed with significance set at P < .05.

RESULTS

The median overall survival after SRS was 8.8 months (patients with non-small-cell lung cancer), 4.6 months (patients with small-cell lung cancer), 11.3 months (patients with breast cancer), and 4.1 months (patients with melanoma). Primary cancer type, number of brain metastases, and concurrent immunotherapy were significant factors in predicting survival. Local tumor control rate per patient was 97.3% and 94.6% at 6 and 12 months after SRS, respectively. Thirty-six patients underwent additional SRS for new tumor development with a median time after SRS of 5 months. Three patients experienced adverse radiation events.

CONCLUSION

Single-session SRS is a well-tolerated palliative treatment option even in patients with ≥20 brain metastases, achieving local control rate >90% with low risks of neurotoxicity while continuing concurrent systemic oncological care.

Intracerebral and pituitary metastatic eccrine carcinoma: prolonged survival using stereotactic radiosurgery

PURPOSE

Eccrine gland carcinoma (EC) is a rare skin neoplasm that uncommonly spreads to the brain or pituitary gland. We describe the role of multiple stereotactic radiosurgery (SRS) procedures to manage recurrent brain metastases of this rare disease.

MATERIALS AND METHODS

Retrospective chart review was completed to obtain details for this report. The study was performed under IRB study on medical record only and was exempt from patient's consent.

RESULTS AND CONCLUSIONS

A 59-year-old female underwent surgical excision of a right parietal scalp EC. Over the next 13 years, the patient underwent initial fractionated whole brain radiation therapy after she developed multiple brain metastases followed by systemic chemotherapy for extracranial disease. Because of repeated development of new brain disease, three SRS procedures were performed to treat a total of 50 brain metastases and a pituitary metastasis (PM). The patient expired from progressive systemic cancer spread 13 years after her initial surgical excision. Due to the rarity of metastatic EC to the brain, no standard treatment paradigm has emerged. Using multimodality options that included local excision of the original skin tumor, followed by radiation, systemic chemotherapy, and three SRS procedures, long-term survival was possible in this unusual case.

Survival and outcomes in patients with ≥ 25 cumulative brain metastases treated with stereotactic radiosurgery

OBJECTIVE

In the era in which more patients with greater numbers of brain metastases (BMs) are being treated with stereotactic radiosurgery (SRS) alone, it is critical to understand how patient, tumor, and treatment factors affect functional status and overall survival (OS). The authors examined the survival outcomes and dosimetry to critical structures in patients treated with Gamma Knife radiosurgery (GKRS) for ≥ 25 metastases in a single session or cumulatively over the course of their disease.

METHODS

A retrospective analysis was conducted at a single institution. The institution's prospective Gamma Knife (GK) SRS registry was queried to identify patients treated with GKRS for ≥ 25 cumulative BMs between June 2013 and April 2020. Ninety-five patients were identified, and their data were used for analysis. Treatment plans for dosimetric analysis were available for 89 patients. Patient, tumor, and treatment characteristics were identified, and outcomes and OS were evaluated.

RESULTS

The authors identified 1132 patients with BMs in their institutional registry. Ninety-five patients were treated for ≥ 25 cumulative metastases, resulting in a total of 3596 tumors treated during 373 separate treatment sessions. The median number of SRS sessions per patient was 3 (range 1-12 SRS sessions), with nearly all patients (n = 93, 98%) having > 1 session. On univariate analysis, factors affecting OS in a statistically significant manner included histology, tumor volume, tumor number, diagnosis-specific graded prognostic assessment (DS-GPA), brain metastasis velocity (BMV), and need for subsequent whole-brain radiation therapy (WBRT). The median of the mean WB dose was 4.07 Gy (range 1.39-10.15 Gy). In the top quartile for both the highest cumulative number and highest cumulative volume of treated metastases, the median of the mean WB dose was 6.14 Gy (range 4.02-10.15 Gy). Seventy-nine patients (83%) had all treated tumors controlled at last follow-up, reflecting the high and durable control rate. Corticosteroids for tumor- or treatment-related effects were prescribed in just over one-quarter of the patients. Of the patients with radiographically proven adverse radiation effects (AREs; 15%), 4 were symptomatic. Four patients required subsequent craniotomy for hemorrhage, progression, or AREs.

CONCLUSIONS

In selected patients with a large number of cumulative BMs, multiple courses of SRS are feasible and safe. Together with new systemic therapies, the study results demonstrate that the achieved survival rates compare favorably to those of larger contemporary cohorts, while avoiding WBRT in the majority of patients. Therefore, along with the findings of other series, this study supports SRS as a standard practice in selected patients with larger numbers of BMs.

Aggressive Stereotactic Radiosurgery Coupled With Immune and Targeted Therapy for Recurrent Melanoma Brain Metastases: A Case Report and Literature Review

Melanoma is a complex disease with a high propensity for brain metastatic spread. Stereotactic radiosurgery (SRS) is a minimally invasive procedure to treat intracranial metastasis with a high rate of local tumor control. In this report, we describe the ongoing management of a patient with interval development of both new and recurrent brain metastases that required seven SRS procedures for a total of 48 brain metastases during a two-year interval while receiving concurrent immunotherapy with ipilimumab and nivolumab. The most recent imaging of the patient showed three brain areas of likely tumor progression despite maintenance nivolumab, and the treatment was recently changed to encorafenib and binimetinib. Combined management with immunotherapy, initial craniotomy, and repeated SRS for new brain metastases resulted in extended survival while preserving neurological function and reducing adverse treatment effects in a patient with advanced metastatic brain melanoma.

A volume matched comparison of survival after radiosurgery in non-small cell lung cancer patients with one versus more than twenty brain metastases

BACKGROUND

Treatment of patients with a large number of brain metastases using radiosurgery remains controversial. In this study we sought to conduct a volume matched comparison to evaluate the clinical outcome of patients with > 20 brain metastases and compared it with patents with solitary brain tumor form non-small cell lung cancer (NSCLC).

METHODS

Between 2014 and 2020, 26 NSCLC patients (925 tumors) underwent stereotactic radiosurgery (SRS) for > 20 metastases in a single procedure (median margin dose = 16 Gy, median cumulative tumor volume = 4.52 cc); 56 patients underwent SRS for a single metastasis (median margin dose = 18 Gy, median volume = 4.74 cc). The overall survival (OS), local tumor control (LC), adverse radiation effect (ARE) risk, and incidence of new tumor development were compared.

RESULTS

No difference in OS was found between patients with > 20 brain metastases (median OS = 15 months) and patients with solitary metastasis (median OS = 12 months; p = 0.3). In the solitary tumor cohort, two of 56 (3.5%) tumors progressed whereas in the > 20 cohort only 3 of 925 (0.3%) tumors showed progression (*p = 0.0013). The rate of new tumor development was significantly higher in patients with > 20 tumors (***p = 0.0001). No significant difference of ARE rate was found (7.5% for > 20 tumors vs. 8.7% for single metastasis).

CONCLUSIONS

Patients with > 20 tumors showed significantly better LC with similar OS compared to patients with solitary tumors. Current guidelines that restrict the role of SRS to patients with 1-4 tumors should be revised.

Can Polymetastatic Disease Be ARRESTed Using SABR? A Dosimetric Feasibility Study to Inform Development of a Phase 1 Trial

Purpose

Phase 2 randomized trials suggest that stereotactic ablative radiation therapy improves progression-free and overall survival in patients with oligometastatic cancer, with phase 3 trials currently testing stereotactic ablative radiation therapy in up to 10 metastases. Whether stereotactic radiation therapy could provide similar benefits in polymetastatic disease (>10 metastases) is unknown. We sought to evaluate the dosimetric feasibility of using stereotactic radiation therapy in polymetastatic disease in preparation for a phase 1 trial.

Methods and Materials

Five craniospinal computed tomography simulations were used to simulate 24 metastatic targets (n = 2 patients), 30 targets (n = 2 patients), and 50 targets (n = 1 patient) that were not present on the initial scan. Creation of radiation therapy plans was attempted for doses up to 30 Gy in 5 fractions, with de-escalation to 24 Gy/4, 18 Gy/3, 12 Gy/2, or 6 Gy/1 if not feasible based on standardized dose constraints. Plans were created using Raystation for delivery on linear accelerators using volumetric modulated arc therapy and validated using Mobius 3D.

Results

A stereotactic radiation therapy treatment plan was generated for each simulated patient. Dose constraints were met to a dose of 30 Gy in 5 fractions for the patients with 24 and 30 lesions. For the patient with 50 targets, dose de-escalation to 12 Gy in 2 fractions was required to meet lung constraints. Estimated beam-on time varied between 18 and 29 minutes per fraction of 6 Gy. Median D95 planning target volume dosimetry ranged from 96.6% to 97.7% of the prescription dose. The conformity index (R100) range was 0.89 to 0.95, and R50 range was 6.84 to 8.72.

Conclusions

Stereotactic radiation therapy treatment plans meeting standardized dose constraints could be created in the setting of 24 to 50 metastatic lesions using volumetric modulated arc therapy. This safety of this approach is being evaluated in a phase 1 trial (NCT04530513).

Clinical dose profile of Gamma Knife stereotactic radiosurgery for extensive brain metastases

OBJECTIVE

The use of Gamma Knife stereotactic radiosurgery (GKSRS) for the treatment of extensive intracranial metastases has been expanding due to its superior dosimetry and efficacy. However, there remains a dearth of data regarding the dose parameters in actual clinical scenarios. The authors endeavored to calculate the radiation dose to the brain when treating ≥ 15 brain metastases with GKSRS.

METHODS

This retrospective analysis reviewed dosage characteristics for patients requiring single-session GKSRS for the treatment of ≥ 15 brain metastases. Forty-two patients met the inclusion criteria between 2008 and 2017. The median number of tumors at the initial GKSRS procedure was 20 (range 15-39 tumors), accounting for 865 tumors in this study. The median aggregate tumor volume was 3.1 cm3 (range 0.13-13.26 cm3), and the median marginal dose was 16 Gy (range 14-19 Gy).

RESULTS

The median of the mean brain dose was 2.58 Gy (range 0.95-3.67 Gy), and 79% of patients had a dose < 3 Gy. The 12-Gy dose volume was a median of 12.45 cm3, which was equivalent to 0.9% of the brain volume. The median percentages of brain receiving 5 Gy and 3 Gy were 6.7% and 20.4%, respectively. There was no correlation between the number of metastases and the mean dose to the brain (p = 0.8). A greater tumor volume was significantly associated with an increased mean brain dose (p < 0.001). The median of the mean dose to the bilateral hippocampi was 2.3 Gy. Sixteen patients had supplementary GKSRS, resulting in an additional mean dose of 1.4 Gy (range 0.2-3.8 Gy) to the brain.

CONCLUSIONS

GKSRS is a viable means of managing extensive brain metastases. This procedure provides a relatively low dose of radiation to the brain, especially when compared with traditional whole-brain radiation protocols.

Executive summary from American Radium Society's appropriate use criteria on neurocognition after stereotactic radiosurgery for multiple brain metastases

BACKGROUND

The American Radium Society (ARS) Appropriate Use Criteria brain malignancies panel systematically reviewed (PRISMA [Preferred Reporting Items for Systematic Reviews and Meta-Analyses]) published literature on neurocognitive outcomes after stereotactic radiosurgery (SRS) for patients with multiple brain metastases (BM) to generate consensus guidelines.

METHODS

The panel developed 4 key questions (KQs) to guide systematic review. From 11 614 original articles, 12 were selected. The panel developed model cases addressing KQs and potentially controversial scenarios not addressed in the systematic review (which might inform future ARS projects). Based upon quality of evidence, the panel confidentially voted on treatment options using a 9-point scale of appropriateness.

RESULTS

The panel agreed that SRS alone is usually appropriate for those with good performance status and 2-10 asymptomatic BM, and usually not appropriate for >20 BM. For 11-15 and 16-20 BM there was (between 2 case variants) agreement that SRS alone may be appropriate or disagreement on the appropriateness of SRS alone. There was no scenario (among 6 case variants) in which conventional whole-brain radiotherapy (WBRT) was considered usually appropriate by most panelists. There were several areas of disagreement, including: hippocampal sparing WBRT for 2-4 asymptomatic BM; WBRT for resected BM amenable to SRS; fractionated versus single-fraction SRS for resected BM, larger targets, and/or brainstem metastases; optimal treatment (WBRT, hippocampal sparing WBRT, SRS alone to all or select lesions) for patients with progressive extracranial disease, poor performance status, and no systemic options.

CONCLUSIONS

For patients with 2-10 BM, SRS alone is an appropriate treatment option for well-selected patients with good performance status. Future study is needed for those scenarios in which there was disagreement among panelists.

Expanded Radiosurgery Capabilities Utilizing Gamma Knife Icon™

The indications and techniques for the treatment of intracranial lesions continue to evolve with the advent of novel technologies. The Gamma Knife Icon™ (GK Icon™) is the most recent model available from Elekta, providing a frameless solution for stereotactic radiosurgery. At our institution, 382 patients with 3,213 separate intracranial lesions have been treated with frameless stereotactic radiotherapy using the GK Icon. The wide range of diagnoses include brain metastases, meningiomas, arteriovenous malformations, acoustic neuromas, pituitary adenomas, and several other histologies. The ability to perform both frame and frameless treatments on the GK Icon has significantly increased our daily volume by almost 50% on a single machine. Although the frameless approach allows one to take advantage of the precision in radiosurgery, the intricacies regarding treatment with this frameless system are not well established. Our initial experience will help to serve as a guide to those wishing to implement this novel technology in their practice.

A Contemporary Report of Clinical Outcomes in Patients with Melanoma Brain Metastases

Background: Brain metastases are observed in more than 40% of all patients with stage 4 melanoma. In recent years, more extensive use of stereotactic radiation (STRT) and the advent of immune checkpoint inhibitors have positively impacted outcomes in patients with metastatic melanoma.brain metastases. Here, we examined real world clinical outcomes of patients presenting with melanoma brain metastases (MBMs). Methods: This retrospective review evaluated MBMs patients treated at The Ottawa Hospital from April 2000 to July 2017. Clinical, radiologic, pathologic and treatment information were gathered from the electronic medical records. The primary outcome was overall survival. The proportional Cox regression model was employed for survival data, while the Fisher’s exact and Mann–Whitney U tests analyzed the relationship between categorical and continuous data, respectively. Results: This retrospective study included 276 patients. Brain metastases were detected symptomatically in 191 patients (69.2%); the rates of detection by routine screening were 4.6% in the pre-2012 era and 11.7% in the contemporary era (p = 0.029). Median survival was three months. Predictors of overall survival were age, higher lactate dehydrogenase (LDH) values, multiple brain lesions, more extensive extracranial disease, neurological symptoms, infratentorial lesions and treatment type. Multivariable analysis demonstrated that stereotactic radiotherapy (STRT) was associated with a hazard ratio of 0.401 (p < 0.001) for survival; likewise, immune checkpoint inhibitor therapy was associated with a hazard ratio of 0.375 (p < 0.001). Conclusion: The findings from this study as “real world” data are consistent with results of pivotal clinical trials in MBMs patients and support contemporary locoregional and immunotherapy practices.

Validation of PTV margin for Gamma Knife Icon frameless treatment using a PseudoPatient® Prime anthropomorphic phantom

The Gamma Knife Icon allows the treatment of brain tumors mask-based single-fraction or fractionated treatment schemes. In clinic, uniform axial expansion of 1 mm around the gross tumor volume (GTV) and a 1.5 mm expansion in the superior and inferior directions are used to generate the planning target volume (PTV). The purpose of the study was to validate this margin scheme with two clinical scenarios: (a) the patient's head remaining right below the high-definition motion management (HDMM) threshold, and (b) frequent treatment interruptions followed by plan adaptation induced by large pitch head motion. A remote-controlled head assembly was used to control the motion of a PseudoPatient® Prime head phantom; for dosimetric evaluations, an ionization chamber, EBT3 films, and polymer gels were used. These measurements were compared with those from the Gamma Knife plan. For the absolute dose measurements using an ionization chamber, the percentage differences for both targets were less than 3.0% for all scenarios, which was within the expected tolerance. For the film measurements, the two-dimensional (2D) gamma index with a 2%/2 mm criterion showed the passing rates of ≥87% in all scenarios except the scenario 1. The results of Gel measurements showed that GTV (D₁₀₀ ) was covered by the prescription dose and PTV (D₉₅ ) was well above the planned dose by up to 5.6% and the largest geometric PTV offset was 0.8 mm for all scenarios. In conclusion, the current margin scheme with HDMM setting is adequate for a typical patient's intrafractional motion.

Laser Interstitial Thermal Therapy for Metastatic Melanoma After Failed Radiation Therapy: A Case Series

BACKGROUND

Laser interstitial thermal therapy (LITT) is a growing technology to treat a variety of brain lesions. It offers an alternative to treatment options, such as open craniotomy and stereotactic radiosurgery.

OBJECTIVE

To analyze our experience using LITT for metastatic melanoma.

METHODS

This is a retrospective chart review of the patients from our institution. Our case series involves 5 patients who had previously failed radiation treatment.

RESULTS

Our patients have low complication rates and short hospital stays. Both are considerably lower when compared to the literature for metastatic melanoma.

CONCLUSION

LITT is a safe therapy, with few complications and short hospital stays.

Adherence of US Insurance Payer Policies to the American Society of Radiation Oncology Stereotactic Radiosurgery Model Policy

PURPOSE

The medical necessity of stereotactic radiosurgery (SRS) is nonuniform across insurance policies. The American Society for Radiation Oncology (ASTRO) created a model policy based on the consensus of the radiation oncology community to communicate medically necessary indications for SRS. We compared the current insurance policies for SRS with those of the ASTRO model policy.

METHODS AND MATERIALS

We identified 58 insurance payers and 3 national benefits managers with SRS policies. Among these, 7 insurance payers were excluded for policies that were not reviewed after 2015 and for not detailing individual medically necessary indications. For each of the indications listed in ASTRO's model policy, we determined the proportion of payers that considered SRS medically necessary. We compared these proportions for national versus regional payers and policies updated in the last 12 months versus those updated less often using Fisher exact and χ² tests.

RESULTS

All insurance policies reviewed considered SRS as medically necessary for brain metastases, medically refractory trigeminal neuralgia, and arteriovenous malformations. Compared with national payers, regional payers were less likely to deem other schwannomas, and a boost for large cranial or spinal lesions medically necessary (P < .05). The indication with the lowest coverage was medically refractory movement disorders (44.4%), followed by medically refractory epilepsy (33.3%). However, policies that were updated within the last year were more likely to deem medical necessity for epilepsy, movement disorders, hemangioblastoma, pineal gland tumors, and other schwannomas.

CONCLUSIONS

Significant discrepancy remains among insurance policies for several indications in ASTRO's model policy for SRS; however, national payers and those with recent policy updates have a greater concordance with the ASTRO model policy.