Frameless Angiography-Based Gamma Knife Stereotactic Radiosurgery for Cerebral Arteriovenous Malformations: A Proof-of-Concept Study

BACKGROUND

Traditional Gamma Knife radiosurgery (GKRS) of brain arteriovenous malformations (AVMs) using digital subtraction angiography (DSA) requires head immobilization using a stereotactic frame.

OBJECTIVE

We describe our protocol of frameless GKRS using DSA while maintaining high spatial resolution for precision.

METHODS

This study is a retrospective review of patients with unruptured AVMs who underwent frameless GKRS. Magnetic resonance imaging and 3-dimensional DSA were obtained without a stereotactic frame for all patients. The imaging studies were merged for contouring of the AVM nidus. During GKRS treatment, patients were immobilized using an individually molded thermoplastic mask.

RESULTS

Thirty-one patients were included in the analysis. The median age is 45.0 years (interquartile range [IQR]: 28.0-55.0). The median nidus size is 3.0 cm (IQR: 2.0-3.4). One patient had a Spetzler-Martin grade I, 11 had a grade II, 11 had a grade III, 6 had a grade IV, and 2 had a grade V AVM. Eleven patients underwent preradiosurgical embolization, 3 patients had previous microsurgical resection and/or embolization, and 1 patient had prior radiosurgery. The median administered dose was 20 Gy (IQR: 18.0-21.0). All patients completed their treatment with the planned radiation dose without complications.

CONCLUSION

This is the first study that integrates DSA in the treatment planning of brain AVMs using GKRS without utilizing a stereotactic head frame. Frameless GKRS provides numerous advantages over frame-based techniques including improved patient experience and the capability of fractionation and thus expanding the eligibility of more AVMs for radiosurgery, while maintaining high spatial resolution of the AVM using angiography data.

Microsurgery versus stereotactic radiosurgery for small petroclival meningiomas presenting with intractable trigeminal neuropathy: A historical cohort study

BACKGROUND

Data on the outcomes of microsurgical resection (SR) and stereotactic gamma knife radiosurgery (GKRS) in patients with trigeminal neuralgia associated with small petrous apex meningiomas are scarce.

OBJECTIVE

We conducted this study to evaluate the pain relief, tumor control, and procedure costs following SR and GKRS for small petroclival meningiomas (less than 3 cm in maximal diameter) using real-world data from our center in Egypt.

MATERIAL AND METHODS

We conducted a retrospective cohort study of 47 patients with small petrous apex meningiomas presenting with intractable trigeminal nerve pain (SR: n = 22 and GKRS: n = 25). Data regarding pain relief on Barrow Neurological Institute (BNI), procedure cost, and tumor control were retrieved and analyzed using appropriate statistical tests.

RESULTS

Patients who underwent SR had lower median BNI pain intensity scores compared to those patients who underwent GKRS, and a significantly higher proportion of patients in the SR group had good BNI scores compared to those in GKRS group (P < 0.05); however, the total costs of SR were significantly less than GKRS (30,519$ vs. 92,372$, respectively).

CONCLUSION

Both SR and GKRS provide pain relief and tumor control in patients with trigeminal neuralgia associated with petrous apex meningioma. However, in the present study, SR achieved better pain control and was more affordable than GKRS.

Quantification of tumor response of cystic vestibular schwannoma to Gamma Knife radiosurgery by using artificial intelligence

OBJECTIVE

Gamma Knife radiosurgery (GKRS) is a common treatment modality for vestibular schwannoma (VS). The ability to predict treatment response is important in patient counseling and decision-making. The authors developed an algorithm that can automatically segment and differentiate cystic and solid tumor components of VS. They also investigated associations between the quantified radiological features of each component and tumor response after GKRS.

METHODS

This is a retrospective study comprising 323 patients with VS treated with GKRS. After preprocessing and generation of pretreatment T2-weighted (T2W)/T1-weighted with contrast (T1WC) images, the authors segmented VSs into cystic and solid components by using fuzzy C-means clustering. Quantitative radiological features of the entire tumor and its cystic and solid components were extracted. Linear regression models were implemented to correlate clinical variables and radiological features with the specific growth rate (SGR) of VS after GKRS.

RESULTS

A multivariable linear regression model of radiological features of the entire tumor demonstrated that a higher tumor mean signal intensity (SI) on T2W/T1WC images (p < 0.001) was associated with a lower SGR after GKRS. Similarly, a multivariable linear regression model using radiological features of cystic and solid tumor components demonstrated that a higher solid component mean SI (p = 0.039) and a higher cystic component mean SI (p = 0.004) on T2W/T1WC images were associated with a lower SGR after GKRS. A larger cystic component proportion (p = 0.085) was associated with a trend toward a lower SGR after GKRS.

CONCLUSIONS

Radiological features of VSs on pretreatment MRI that were quantified using fuzzy C-means were associated with tumor response after GKRS. Tumors with a higher tumor mean SI, a higher solid component mean SI, and a higher cystic component mean SI on T2W/T1WC images were more likely to regress in volume after GKRS. Those with a larger cystic component proportion also trended toward regression after GKRS. Further refinement of the algorithm may allow direct prediction of tumor response.

Gamma Knife® stereotactic radiosurgery as a treatment for essential and parkinsonian tremor: long-term experience

INTRODUCTION

Unilateral Gamma Knife™ stereotactic radiosurgery on the ventral-intermediate nucleus of the thalamus is a minimally invasive neurosurgical option for refractory tremor. We describe the experience of Gamma Knife™ thalamotomy (GKT) in patients with essential tremor (ET) and tremor-dominant Parkinson's disease (PD) at our specialised stereotactic neurosurgery unit.

METHODS

We reviewed the cases of patients treated with GKT between January 2014 and February 2018 with a minimum of 12 months' follow-up. We analysed clinical and demographic variables, indication, radiation dose, effectiveness (based on subscales of the Fahn-Tolosa-Marin [FTM] scale and the Movement Disorders Society-Unified Parkinson's Disease Rating Scale [MDS-UPDRS] motor score), and adverse events.

RESULTS

Thirteen patients were registered, 6 with a diagnosis of tremor-dominant PD, four with refractory ET, and three with ET and PD. Median age was 78 years (range, 62-83), with seven patients aged over 75 years. Four patients were receiving anticoagulants and two had history of stroke. The maximum radiation dose administered was 130 Gy. Mean (standard deviation) follow-up duration was 30.0 (14.5) months. Significant tremor improvement was observed on the FTM subscales: 63.6% at 12 months and 63.5% at the end of follow-up; MDS-UPDRS tremor items showed improvements of 71.3% at 12 months and 60.3% at the end of follow up. Eleven patients reported significant improvements in quality of life, and 3 reported mild and transient adverse effects.

CONCLUSIONS

This is the largest series of patients with essential and parkinsonian tremor treated with GKT and followed up in the long term in Spain. GKT can be safe and effective in the long term in patients with refractory tremor, including in elderly patients and those receiving anticoagulants.

Stereotactic radiosurgery for cerebral cavernous malformation: comparison of hemorrhage rates before and after stereotactic radiosurgery

OBJECTIVE

Cerebral cavernous malformation (CM) is an angiographically occult vascular pathology. Although microsurgery is the gold standard treatment to control the symptoms of CM, resection carries high risk in some situations, especially eloquent areas. The objective was to evaluate annual hemorrhage rates (AHRs) before and after stereotactic radiosurgery (SRS) treatment of cerebral CM in different locations.

METHODS

A total of 195 patients (119 women and 76 men) with CM treated at the Gazi University Gamma Knife Center between April 2005 and June 2017 were analyzed. The mean ± SD follow-up period was 67.4 ± 31.1 months (range 12 days to 170 months). AHR before SRS, AHR after SRS, morbidity associated with radiation, seizure control rate after SRS, lesion volume, coexistence with developmental venous anomaly, and SRS treatment parameters were analyzed, with evaluation of radiological data and clinical charts performed retrospectively. The seizure control rate was assessed using the Engel outcome scale.

RESULTS

The AHR before SRS was 15.3%. Application of SRS to these patients significantly reduced the AHR rates to 2.6% during the first 2 years after treatment and to 1.4% thereafter. Favorable seizure control (Engel class I and II) after radiosurgery was achieved in 23 patients (88.5%) with epilepsy. Radiation-related temporary complications occurred in 15.4% of patients, and permanent morbidity occurred in 4.6%.

CONCLUSIONS

SRS is a safe and effective treatment modality for reducing the hemorrhage risk of CM. The authors suggest that SRS should be considered for the treatment of patients with CM, high surgical risks, and hemorrhage history, instead of a using a wait-and-see policy.

Gamma Knife radiosurgery for tuberculum sellae meningiomas: a series of 78 consecutive patients

Outcomes of Gamma Knife radiosurgery (GKRS) for tuberculum sellae meningiomas (TSMs) have not been reported explicitly within any meningioma series. We present the first and largest TSM series with clinical, radiosurgical, and outcome features for 78 consecutive patients managed with GKRS. Patients who underwent GKRS for TSMs between 2005 and 2021 and had a minimum of 6 months of follow-up were included. Medical records, imaging studies, and follow-up examinations were evaluated retrospectively. A total of 78 patients with a median age of 50.5 years were included. SRS was conducted as an upfront treatment for 38 patients (48.7%). The median target volume was 1.7 cm³ (range, 0.1-14.6). During a median follow-up of 78.5 months, the cumulative PFS rates of the whole cohort at 1, 5, and 10 years by Kaplan-Meier analysis were 100%, 97.9%, and 94.5%, respectively. Of 47 patients with impaired vision, improvement and/or preservation of visual acuity, and visual field were achieved in 55.3% and 42.6%, respectively. No new-onset hormonal deficits were observed. Based on our data, SRS represents an effective and safe modality for unresected or recurrent/residual TSMs. SRS should be offered to patients who are not willing or not ideal candidates for surgery.

Gamma Knife radiosurgery for the treatment of cluster headache: a systematic review

Cluster headache (CH) is a severe trigeminal autonomic cephalalgia that, when refractory to medical treatment, can be treated with Gamma Knife radiosurgery (GKRS). The outcomes of studies investigating GKRS for CH in the literature are inconsistent, and the ideal target and treatment parameters remain unclear. The aim of this systematic review is to evaluate the safety and the efficacy, both short and long term, of GKRS for the treatment of drug-resistant CH. A systematic review of the literature was performed to identify all clinical articles discussing GKRS for the treatment of CH. The literature review revealed 5 studies describing outcomes of GKRS for the treatment of CH for a total of 52 patients (48 included in the outcome analysis). The trigeminal nerve, the sphenopalatine ganglion, and a combination of both were treated in 34, 1, and 13 patients. The individual studies demonstrated initial meaningful pain reduction in 60-100% of patients, with an aggregate initial meaningful pain reduction in 37 patients (77%). This effect persisted in 20 patients (42%) at last follow-up. Trigeminal sensory disturbances were observed in 28 patients (58%) and deafferentation pain in 3 patients (6%). Information related to GKRS for CH are limited to few small open-label studies using heterogeneous operative techniques. In this setting, short-term pain reduction rates are high, whereas the long-term results are controversial. GKRS targeted on the trigeminal nerve or sphenopalatine ganglion is associated to a frequent risk of trigeminal disturbances and possibly deafferentation pain.

Conclusions

This chapter considers current controversies and observations from the past for which no current explanation is available.

Impact of Social Determinants of Health on Stereotactic Radiotherapy for Vestibular Schwannoma

OBJECTIVES/HYPOTHESIS

Linear accelerator (LINAC) and Gamma Knife (GK) are common stereotactic radiation therapies for treating vestibular schwannoma (VS). There is currently limited literature examining specific demographic and socioeconomic factors, which influence the type of stereotactic radiation therapy a patient with VS receives.

STUDY DESIGN

Retrospective database review.

METHODS

The National Cancer Database was queried for cases of VS between 2004 and 2016. Patient demographic characteristics were compared using chi-squared and t-tests between GK and LINAC treated groups. Multivariate regression analysis was performed to assess predictors of stereotactic radiation therapy received.

RESULTS

Of the 6,208 included patients, 5,306 (85.5%) received GK and 902 (14.5%) received LINAC. The mean age of GK patients was significantly lower than that of LINAC patients (58.0 vs. 59.7, P < .001). Individuals treated with GK had greater proportions of private insurance (P < .001) and incomes greater than $63,332 (P = .003). A greater proportion of GK patients were treated in academic centers (P < .001), in high-volume facilities (P < .001), in metropolitan areas (P < .001), and in the Northeastern United States (P < .001). On multivariate logistic regression analysis, region, metropolitan area, facility type, tumor size, and distance traveled by patients independently predict receipt of GK versus LINAC.

CONCLUSION

Differences in patient demographics and other social determinants of health influence choice of GK versus LINAC therapy for VS patients. Future studies focused on addressing barriers to care, which may influence postprocedural quality of life and clinical outcomes associated with these two treatments are necessary to better understand the impact of these social differences.

LEVEL OF EVIDENCE

4 Laryngoscope, 2022.

Lee J. Gamma Knife radiosurgery for trigeminal neuralgia provides greater pain relief at higher dose rates

In Gamma Knife (GK) radiosurgery, dose rate decreases during the life cycle of its radiation source, extending treatment times. Prolonged treatments influence the amount of sublethal radiation injury that is repaired during exposure, and is associated with decreased biologically-equivalent dose (BED). We assessed the impact of treatment times on clinical outcomes following GK of the trigeminal nerve - a rare clinical model to isolate the effects of treatment times. This is a retrospective analysis of 192 patients with facial pain treated across three source exchanges. All patients were treated to 80 Gy with a single isocenter. Treatment time was analyzed in terms of patient anatomy-specific dose rate, as well as BED calculated from individual patient beam-on times. An outcome tool measuring pain in three distinct domains (pain intensity, interference with general and oro-facial activities of daily living), was administered before and after intervention. Multivariate linear regression was performed with dose rate/BED, brainstem dose, sex, age, diagnosis, and prior intervention as predictors. BED was an independent predictor of the degree of improvement in all three dimensions of pain severity. A decrease in dose rate by 1.5 Gy/min corresponded to 31.8% less improvement in the overall severity of pain. Post-radiosurgery incidence of facial numbness was increased for BEDs in the highest quartile. Treatment time is an independent predictor of pain outcomes, suggesting that prescription dose should be customized to ensure iso-effective treatments, while accounting for the possible increase in adverse effects at the highest BEDs.

Dose kernel decomposition for spot-based radiotherapy treatment planning

PURPOSE

Pre-calculation of accurate dose deposition kernels for treatment planning of spot-based radiotherapies, such as Gamma Knife (GK) and Gamma Pod (GP), can be very time-consuming and may require large data storage with an enormous number of possible spots. We proposed a novel kernel decomposition (KD) model to address accurate and fast (real-time) dose calculation with reduced data storage requirements for spot-based treatment planning. The application of the KD model was demonstrated for clinical GK and GP radiotherapy platforms.

METHODS

The dose deposition kernel at each spot (shot position) is modeled as the product of a shift-invariant kernel based on a reference kernel and spatially variant scale factor. The reference kernel, one for each collimator, is defined at the center of the commissioning phantom for GK and at the center of the treatment target for GP and calculated using the Monte Carlo (MC) method. The spatially variant scale factor is defined as the ratio of the mean tissue maximum ratio (TMR) at the candidate shot position to that at the reference kernel position, and the mean TMR map is calculated within the entire volume through parallel beam ray tracing on the density image followed by averaging over all source directions. The proposed KD dose calculations were compared with the MC method and with the GK and GP treatment planning system (TPS) computations for various shot positions and collimator sizes utilizing a phantom and 14 and 12 clinical plans for GK and GP, respectively.

RESULTS

For the phantom study, the KD Gamma index (3%/1 mm) passing rates were greater than 99% (median 100%) relative to the MC doses, except for the shots close to the boundary. The passing rates dropped below 90% for 8 mm (16 mm) shots positioned within ∼1 cm (∼2 cm) of the boundary. For the clinical GK plans, the KD Gamma passing rates were greater than 99% (median 100%) compared to the MC and greater than 92% (median 99%) compared to the TPS. For the clinical GP plans, the KD Gamma passing rates were greater than 95% (median 98%) compared to the MC and greater than 91% (median 97%) compared to the TPS. The scale factors were calculated in sub-seconds with GPU implementation and only need to be calculated once before treatment plan optimization. The calculation of the dose kernel was also within sub-seconds without requiring beam-by-beam calculation commonly done in the TPS.

CONCLUSION

The proposed model can provide an accurate dose and enables real-time dose and derivative calculations by kernel shifting and scaling without pre-calculating or requiring large data storage for GK and GP dose deposition kernels during treatment planning. This model could be useful for spot-based radiotherapy treatment planning by allowing an efficient global fine search for optimal spots.

Treatment Outcomes of Gamma-Knife Radio Surgery in Refractory Obsessive-Compulsive Disorder

Background

Obsessive-compulsive disorder (OCD) is a common disease that has negative effects on functionality, and 10% of the patients do not respond to first-line treatments. Gamma-knife radiosurgery (GKRS) has been used in patients with treatment-resistant OCD, but the data on long-term outcomes are still unsatisfactory.

Methods

In this study, 12 patients who underwent GKRS between 2005 and 2020 were evaluated retrospectively. Anterior capsulotomy was performed using two 4-mm isocenters at the midputaminal point of the anterior limb of the internal capsule on each side with a maximum radiation dose of 140-180 Gy. Patients were followed up with the Yale-Brown Obsession and Compulsion Scale (Y-BOCS), Montgomery-Asberg Depression Rating Scale (MADRS), and Brief Psychiatric Rating Scale (BPRS) on the first, third, and sixth months.

Results

After the procedure, a 35% reduction was observed in the overall Y-BOCS scores, and full response rate was 50%. There was a 49.5% decrease in the MADRS scores and a 57.8% decrease in the BPRS.

Conclusion

GKRS is an effective and non-invasive procedure with favorable side effects in treatment-resistant OCD with selected patients.

Intracranial Dural Arteriovenous Fistulas with Cortical Venous Drainage: Radiosurgery as an Effective Alternative Treatment

OBJECTIVE

To evaluate the clinical and radiological outcome of Gamma Knife radiosurgery (GKS) in treatment of intracranial dural arteriovenous fistula (DAVF) with cortical venous drainage (CVD) and compare it with the outcome of endovascular therapy.

METHODS

Patients who underwent GKS or endovascular therapy for intracranial DAVF with CVD over 10 years (January 2007 to December 2016) at the All India Institute of Medical Sciences, New Delhi, were included. Demographics, clinical presentation, imaging details, and follow-up clinical status were reviewed retrospectively. Clinical follow-up was conducted once every 6 months. Radiological follow-up using digital subtraction angiography was performed at a mean 24 months after intervention. Patients with clinical follow-up of <1 year were excluded from the study.

RESULTS

The study included 35 patients (26 in embolization group and 9 in GKS group) who had intracranial DAVF with CVD were included in the study. Clinical improvement was seen in 77.78% of the patients who received GKS and 57.7% of the patients who underwent embolization (P = 0.431). Complete obliteration of DAVF was seen in 55.56% of the patients in the GKS group and 57.7% of the patients in the embolization group (P = 1). GKS was at least as effective as embolization in terms of clinical and radiological outcome in treatment of intracranial DAVF with CVD.

CONCLUSIONS

Contrary to popular perception, GKS should be considered as an effective first-line treatment alternative of intracranial DAVF with CVD.

Is Real-Time Inverse Planning Optimizing Dose to the Normal Brain? A Prospective Comparative Trial in a Series of Brain Metastases Treated by Stereotactic Radiosurgery

BACKGROUND

Radiosurgery has demonstrated good safety and efficacy in the treatment of multiple brain metastases (BMs). However, multi-target dose planning can be challenging and time-consuming. A recently developed real-time inverse treatment planning (IP) by convex optimization has been demonstrated to produce high-quality treatment plans with good conformity and selectivity in single-target plans. We intended to test the capacity of this IP to rapidly generate efficient plans while optimizing the preservation of normal tissue in multiple BM.

METHODS

Seventy-nine patients (mean age 62.4, age range 22-85) with a total of 272 BMs were treated by Gamma Knife Radiosurgery. All subjects were treated using a forward planning (FP) technique by an expert neurosurgeon. The new Intuitive Plan was applied and able to automatically generate an alternative plan for each patient. All planning variables were collected from the IP to be compared with the corresponding measurements obtained from the FP. A paired sample t test was applied to compare the 2 plans for the following variables: brain volumes receiving 10 Gy (V10) (primary endpoint), and 12 Gy (V12), planning indices (selectivity, coverage, gradient, and Paddick Conformity Index [PCI]), beam-on time (BOT), and integral doses. Additionally, the noninferiority margin for each item was calculated, and the 2 plans were compared for noninferiority using a paired t test.

RESULTS

The mean age of patients was 62.4 years old (age range 22-85), with a sex ratio of 1.02. The average number of lesions per patient was 3.4 (range 1-12). The mean prescription dose was 21.46 Gy (range 14-24 Gy). Noninferiority of the IP was concluded for V10, V12, prescription isodose volume, BOT, PCI, and selectivity. The V10 (and V12) was significantly lower with the IP (p < 0.001). These volumes were 8.69 cm3 ± 11.39 and 5.47 cm3 ± 7.03, respectively, for the FP and 7.57 cm3 ± 9.44 and 4.78 cm3 ± 5.86 for the IP. Only the coverage was significantly lower with the IP (-2.3%, p < 0.001), but both selectivity (+17%) and PCI (+15%) were significantly higher with the IP than FP (p < 0.001).

CONCLUSION

This IP demonstrated its capacity to generate multi-target plans rapidly, with a dose to the brain (V10) and BOT noninferior to the one of a human expert planner. These results would benefit from confirmation in a larger prospective series.

Stereotactic radiosurgery for craniopharyngiomas

BACKGROUND

The management of craniopharyngiomas is challenging, usually requiring multidisciplinary care. We evaluated the long-term clinical and radiologic outcomes of Gamma Knife radiosurgery (GKRS) for craniopharyngiomas.

METHODS

This retrospective study involved patients managed with GKRS for a craniopharyngioma during the period of 1989 to 2019. Patient clinical and radiologic data, tumor characteristics, and procedural details were analyzed.

RESULTS

Thirty-eight consecutive patients (24 males; mean patient age at GKRS = 30.82 years [SD ± 20.45 years]) were treated with GKRS for craniopharyngioma. Overall survival rates at 5 and 10 years were 84.1% and 80.1%, respectively. Progression-free survival at 5 years was 48.1%, and, at 10 years, it was 29.8%. Risk factors for post-GKRS clinical deterioration were increasing number of isocenters used (p = 0.04 (HR1.32, CI 1-1.73)), increasing margin dose [p = 0.02 (HR1.52, CI 1.31-1.84)], and maximum dose > 35 Gy [p = 0.002 (HR1.35, CI 1.11-1.63)].

CONCLUSION

Stereotactic radiosurgery (SRS) appears a safe and effective management option in selected craniopharyngioma patients. Increasing margin dose and maximum dose > 35 Gy are associated with an increased risk for post-SRS neurologic deficit. Further, well-designed studies are necessary to determine the optimal timing and SRS parameters and to identify which patients with craniopharyngioma will benefit the most from SRS.

Gamma Knife radiosurgery as primary treatment of low-grade brainstem gliomas: A systematic review and metanalysis of current evidence and predictive factors

The current standard of care for surgically inaccessible low-grade brainstem gliomas (BS-LLGs) is external-beam radiotherapy (RT). Developments toward more innovative conformal techniques have focused on decreasing morbidity, by limiting radiation to surrounding tissues. Among these Gamma Knife radiosurgery (SRS-GK) has recently gained an increasingly important role in the treatment of these tumors. Although SRS-GK has not yet been compared with conventional RT in patients harboring focal BS-LGGs, clinical practice has been deeply influenced by trials performed on other tumors. This is the first meta-analysis on the topic, systematically reviewing the most relevant available evidence, comparing RT and SRS-GK as primary treatments of BS-LGGs, focusing on survival, clinical outcome, oncological control, and complications. Predictive factors have been systematically evaluated and analyzed according to statistical significance and clinical relevance.

Systematic evaluation and plan quality assessment of the Leksell® gamma knife® lightning dose optimizer

To compare stereotactic radiosurgery (SRS) plan quality metrics of manual forward planning (MFP) and Elekta Fast Inverse Planning™ (FIP)-based inversely optimized plans for patients treated with Gamma Knife®. Clinically treated, MFP SRS plans for 100 consecutive patients (115 lesions; 67 metastatic and 48 benign) were replanned with the FIP dose optimizer based on a convex linear programming formulation. Comparative plans were generated to match or exceed the following metrics in order of importance: Target Coverage (TC), Paddick Conformity Index (PCI), beam-on time (BOT), and Gradient Index (GI). Plan quality metrics and delivery parameters between MFP and FIP were compared for all lesions and stratified into subgroups for further analysis. Additionally, performance of FIP for multiple punctate (<4 mm) metastatic lesions on a subset of cases was investigated. A Wilcoxon signed-rank test for non-normal distributions was used to assess the statistical differences between the MFP and FIP treatment plans. Overall, 76% (87/115) of FIP plans showed a statistically significant improvement in plan quality compared to MFP plans. As compared to MFP, FIP plans demonstrated an increase in the median PCI by 1.1% (p<0.01), a decrease in GI by 3.7% (p< 0.01), and an increase in median number of shots by 74% (p< 0.01). TC and BOT were not statistically significantly different between MFP and FIP plans (p>0.05). FIP plans showed a statistically significant increase in use of 16 mm (p< 0.01) and blocked shots (p< 0.01), with a corresponding decrease in 4 mm shots (p< 0.01). Use of multiple shots per coordinate was significantly higher in FIP plans (p<0.01). The FIP optimizer failed to generate a clinically acceptable plan in 4/115 (3.5%) lesions despite optimization parameter changes. The mean optimization time for FIP plans was 5.0 min (Range: 1.0 - 10.0 min). In the setting of multiple punctate lesions, PCI for FIP was significantly improved (p<0.01) by changing the default low-dose/BOT penalty optimization setting from a default of 50/50 to 75-85/40. FIP offers a significant reduction in manual effort for SRS treatment planning while achieving comparable plan quality to an expert planner-substantially improving overall planning efficiency. FIP plans employ a non-intuitive increased use of blocked sectors and shot-in-shot technique to achieve high quality plans. Several FIP plans failed to achieve clinically acceptable treatments and warrant further investigation.

Clinical and radiologic outcomes after stereotactic radiosurgery for meningiomas in direct contact with the optic apparatus: an international multicenter study

OBJECTIVE

Resection of meningiomas in direct contact with the anterior optic apparatus carries risk of injury to the visual pathway. Stereotactic radiosurgery (SRS) offers a minimally invasive alternative. However, its use is limited owing to the risk of radiation-induced optic neuropathy. Few SRS studies have specifically assessed the risks and benefits of treating meningiomas in direct contact with the optic nerve, chiasm, or optic tract. The authors hypothesized that SRS is safe for select patients with meningiomas in direct contact with the anterior optic apparatus.

METHODS

The authors performed an international multicenter retrospective analysis of 328 patients across 11 institutions. All patients had meningiomas in direct contract with the optic apparatus. Patients were followed for a median duration of 56 months after SRS. Neurological examinations, including visual function evaluations, were performed at follow-up visits. Clinical and treatment variables were collected at each site according to protocol. Tumor volumes were assessed with serial MR imaging. Variables predictive of visual deficit were identified using univariable and multivariable logistic regression.

RESULTS

SRS was the initial treatment modality for 64.6% of patients, and 93% of patients received SRS as a single fraction. Visual information was available for 302 patients. Of these patients, visual decline occurred in 29 patients (9.6%), of whom 12 (41.4%) had evidence of tumor progression. Visual decline in the remaining 17 patients (5.6%) was not associated with tumor progression. Pre-SRS Karnofsky Performance Status predicted visual decline in adjusted analysis (adjusted OR 0.9, 95% CI 0.9-1.0, p < 0.01). Follow-up imaging data were available for 322 patients. Of these patients, 294 patients (91.3%) had radiographic evidence of stability or tumor regression at last follow up. Symptom duration was associated with tumor progression in adjusted analysis (adjusted OR 1.01, adjusted 95% CI 1.0-1.02, adjusted p = 0.02).

CONCLUSIONS

In this international multicenter study, the vast majority of patients exhibited tumor control and preservation of visual function when SRS was used to treat meningioma in direct contact with the anterior optic pathways. SRS is a relatively safe treatment modality for select patients with perioptic meningiomas in direct contact with the optic apparatus.

Dosimetric Comparison, Treatment Efficiency Estimation, and Biological Evaluation of Popular Stereotactic Radiosurgery Options in Treating Single Small Brain Metastasis

Objectives

This study aimed to show the advantages of each stereotactic radiosurgery (SRS) treatment option for single small brain metastasis among Gamma Knife (GK), Cone-based VMAT (Cone-VMAT), and MLC-based CRT (MLC-CRT) plans.

Materials and Methods

GK, Cone-VMAT, and MLC-CRT SRS plans were retrospectively generated for 11 patients with single small brain metastasis whose volume of gross tumor volume (GTV) ranged from 0.18 to 0.76 cc (median volume 0.60 cc). Dosimetric parameters, treatment efficiency, and biological parameters of the three techniques were compared and evaluated. The metric variation with the planning target volume (PTV) was also studied.

Results

The conformity index (CI) was similar in GK and MLC-CRT plans, higher than Cone-VMAT. Cone-VMAT achieved comparable volume covered by 12 Gy (V12) and gradient index (GI) as GK, lower than MLC-CRT. The heterogeneity index (HI) of GK, Cone-VMAT, and MLC-CRT decreased sequentially. GK gave the lowest volume covered by 3 Gy (V3) and 6 Gy (V6), while MLC-CRT got the highest. The beam-on time and treatment time of GK, Cone-VMAT, and MLC-CRT decreased in turn. Tumor control probability (TCP) of all three SRS plans was greater than 98%, and normal tissue complication probability (NTCP) of all organs at risk (OARs) was below 0.01%. GK and Cone-VMAT resulted in superior TCP and NTCP of the normal brain tissue than MLC-CRT. The relative value of Cone-VMAT and GK for all metrics hardly changed with the target volume. Except for the unchanged HI and TCP, the other results of MLC-CRT with respect to GK improved as the target volume increased. MLC-CRT could produce higher CI than GK and Cone-VMAT when the target volume increased above 2 and 1.44 cc, respectively.

Conclusion

For single small brain metastases, Cone-VMAT may be used as an alternative to GK-free centers. In addition to the advantage of short treatment time, MLC-CRT showed superiority in CI as the target volume increased. Treatment centers can choose appropriate SRS technique on a case-by-case basis according to institutional conditions and patients’ individual needs.

Gamma Knife radiosurgery as salvage therapy for gangliogliomas after initial microsurgical resection

INTRODUCTION

Gangliogliomas (GG) are considered WHO grade I rare tumors. While they commonly manifest as temporal lobe epilepsy, they can be located anywhere in the brain. Primary treatment is complete microsurgical resection. Remnant or recurrent GG can benefit from radiation therapy. Here, we present a series of GG who received Gamma Knife radiosurgery (GKR) after initial microsurgery.

METHODS

Between October 2009 and February 2020, four patients benefitted from such approach. The median age at surgery was 16 years (mean 17, 11-25) and at the time of GKR was 22.5 years (mean 23, 19-28). Initial clinical symptom was epilepsy in 3 cases and incidental in one. Biopsy was firstly performed in one case. One patient had stereotactic electroencephalography. The respective anatomical locations were right parieto-occipital, sylvian, left paraventricular and left inferior parietal.

RESULTS

Gamma Knife radiosurgery was performed after a median time of 3.5 years after initial gross total microsurgical resection (GTR). The median follow-up after GKR was 54 months (mean 58.5, 6-120). The median marginal dose was 18 Gy (mean 17.5, 16-18). The median target volume was 0.5 mL (mean 0.904, 0.228-2.3). The median prescription isodose volume was 0.6 mL (mean 0.9, 0.3-2.4). At last follow-up, GG majorly decreased in 3 patients, remained stable in one.

CONCLUSION

Gamma Knife radiosurgery is safe and effective for remnant GG after GTR. Primary treatment remains microsurgical resection, especially in cases with symptomatic mass effect or with epilepsy. Single fraction GKR can be a valuable option for remnant or recurrent tumors after initial resection.

Evaluating the impact of prescription isodose line on plan quality using Gamma Knife inverse planning

The impact of selection of prescription isodose line (IDL) on plan quality has not been well evaluated during inverse planning (IP). In this study, a total of 180 IP plans at five levels of IDL were generated for 30 brain metastases (BMs). For each BM, one round of IP was performed with typical IP settings, followed by a quick fine‐tuning to ensure the same target coverage and comparable conformality index. The impact of the IDL on the quality metrics (selectivity, gradient index [GI], and treatment time) was evaluated. The decrease of selectivity and increase of GI meant inferior target dose conformality and more dose spillage. Additionally, a metric directly correlated to the treatment time was proposed. For all cases, the mean GI decreased monotonically as IDL decreased from 70% to 30%, and the decreasing rate was significantly different based on tumor size. The mean selectivity and number of shots decreased monotonically as IDL decreased for all the tumors. From 70% to 30% IDL, the decreasing rate of the mean selectivity was 2.8% (p = 0.020), 7.7% (p = 0.005), and 15.4% (p = 0.020) and that of the number of shots was 75.4% (p = 0.001), 73.2% (p = 0.001), and 50.7% (p = 0.009), for the large, medium, and small tumors, respectively. For the medium and small tumor groups, the mean treatment time increased monotonically when IDLs decreased (increasing rate was 80.0% [p = 0.002] for medium tumors [p = 0.001] and 130.8% [p = 0.001] for small tumors from 70% to 30%). For the large tumors, the mean treatment time was the shortest at 50% IDL (59.0 min) and higher at 70% (65.9 min) and 30% (71.9 min). Overall, the GammaPlan chose smaller sectors for plans with lower IDLs except for the large size group.

Optimizing stereotactic radiosurgery in patients with recurrent or residual craniopharyngiomas

PURPOSE

Stereotactic radiosurgery (SRS) is an important management strategy for residual and recurrent craniopharyngiomas. The current study evaluated the factors which affected tumor control and complications in craniopharyngioma SRS.

METHODS

This study includes 53 consecutive patients who underwent single-session SRS for recurrent or residual craniopharyngiomas. The median age was 41 years with 28 male and 25 females. The median tumor volume was 0.63 cm³ and median margin dose was 12 Gy (range 9-25 Gy).

RESULTS

The overall 3-, 5-, and 10-year survival rates were 97.8%, 92.7% and 88.5%. The overall 3-, 5-, and 10-year tumor control rates were 81.0%, 72.1%, and 53.4%. In univariate analysis, ≥ 3 mm distance from optic structures (p = 0.002), only solid or cystic tumor type (p = 0.037), and ≥ 12 Gy to ≥ 85% of the tumor (p < 0.001) were significantly associated with improved tumor control. In multivariate analysis, only solid or cystic tumor type, (p = 0.034), and ≥ 85% of the tumor receiving ≥ 12 Gy (p = 0.004) were significantly associated with better tumor control. When ≥ 85% of the tumor received ≥ 12 Gy the tumor control rates at 3-, 5-, and 10-year were 100%, 93.3%, and 93.3%. Higher conformity index was not associated with better tumor control.

CONCLUSIONS

The tumor control rates after recurrent or residual craniopharyngiomas SRS were improved by ensuring that at least 85% of the tumor received ≥ 12 Gy even when the distance between the tumor and the optic system is < 3 mm. This concept refutes the conformity theory that a high conformity index is a critical feature of effective SRS.