Five-fraction Gamma Knife radiosurgery using the Extend relocatable system for benign neoplasms close to optic pathways

Dosimetric predictors of symptomatic radiation necrosis after five-fraction radiosurgery for brain metastases

BACKGROUND

To identify factors predictive of developing symptomatic radiation necrosis (sRN) among patients with either intact or resected brain metastases undergoing five-fraction stereotactic radiosurgery (5fSRS).

METHODS

Multi-institutional retrospective review of 117 brain metastases from 83 patients treated with 5fSRS. The cumulative incidence of sRN and predictors of sRN were calculated using Gray's competing risks and Cox regression.

RESULTS

The median dose of 5fSRS was 30 Gy (range: 25-40), and 21 lesions (18%) had prior SRS. After a median follow-up of 10.3 months (range: 3-52), the cumulative sRN incidence was 15%, with a median time to sRN of 6.9 months (range: 1.8-31.7). sRN incidence was significantly higher among the lesions treated with prior SRS: hazard ratio (HR): 7.48 [95% confidence interval: 2.57-21.8]. Among lesions without prior SRS, higher volume of uninvolved brain receiving 25 Gy (BrainV25; HR: 1.07 [1.02-1.12]) and 30 Gy (BrainV30; HR: 1.07 [1.01-1.33]) were the most significant factors associated with sRN. Similar results were also observed among the patients with prior SRS. For lesions without prior SRS, BrainV25 > 16 cm³ (HR: 11.7 [1.47-93.3]) and BrainV30 > 10 cm³ (HR: 7.08 [1.52-33.0]) were associated with significantly higher risk of sRN. At two years, the sRN incidence was 21% if violating either dosimetric threshold and 2% if violating neither (p = .007).

CONCLUSION

BrainV25 and BrainV30 are significant dosimetric predictors of sRN of brain metastases treated with 5fSRS. In the absence of prior SRS, maintaining BrainV25Gy < 16 cm³ and BrainV30Gy < 10 cm³ may minimize sRN risk.

Fractionated Gamma Knife radiosurgery for skull base meningiomas: a single-institution experience

OBJECTIVEGamma Knife radiosurgery (GKRS) has been successfully used for the treatment of intracranial meningiomas given its steep dose gradients and high-dose conformality. However, treatment of skull base meningiomas (SBMs) may pose significant risk to adjacent radiation-sensitive structures such as the cranial nerves. Fractionated GKRS (fGKRS) may decrease this risk, but until recently it has not been practical with traditional pin-based systems. This study reports the authors' experience in treating SBMs with fGKRS, using a relocatable, noninvasive immobilization system.METHODSThe authors performed a retrospective review of all patients who underwent fGKRS for SBMs between 2013 and 2018 delivered using the Extend relocatable frame system or the Icon system. Patient demographics, pre- and post-GKRS tumor characteristics, perilesional edema, prior treatment details, and clinical symptoms were evaluated. Volumetric analysis of pre-GKRS, post-GKRS, and subsequent follow-up visits was performed.RESULTSTwenty-five patients met inclusion criteria. Nineteen patients were treated with the Icon system, and 6 patients were treated with the Extend system. The mean pre-fGKRS tumor volume was 7.62 cm3 (range 4.57-13.07 cm3). The median margin dose was 25 Gy delivered in 4 (8%) or 5 (92%) fractions. The median follow-up time was 12.4 months (range 4.7-17.4 months). Two patients (9%) experienced new-onset cranial neuropathy at the first follow-up. The mean postoperative tumor volume reduction was 15.9% with 6 patients (27%) experiencing improvement of cranial neuropathy at the first follow-up. Median first follow-up scans were obtained at 3.4 months (range 2.8-4.3 months). Three patients (12%) developed asymptomatic, mild perilesional edema by the first follow-up, which remained stable subsequently.CONCLUSIONSfGKRS with relocatable, noninvasive immobilization systems is well tolerated in patients with SBMs and demonstrated satisfactory tumor control as well as limited radiation toxicity. Future prospective studies with long-term follow-up and comparison to single-session GKRS or fractionated stereotactic radiotherapy are necessary to validate these findings and determine the efficacy of this approach in the management of SBMs.

Estimation of technical treatment accuracy in fractionated stereotactic radiosurgery

Aim:

The purpose of this study was to estimate technical treatment accuracy in fractionated stereotactic radiosurgery (fSRS) using the Extend™ system (ES) of Gamma Knife (GK).

Methods and materials:

The fSRS with GK relies on a re-locatable ES where the reference treatment position is estimated using repositioning check tool (RCT). A patient surveillance unit (PSU) monitors the head and neck movement of the patient during treatment and imaging. The quality assurance test of RCT was performed to evaluate a standard error (SE) associated with a measurement tool called digital probe. A ‘4-mm collimator shot’ dose plan for a head–neck phantom was investigated using EBT3 films. CT and MR distortion measurement studies were combined to evaluate SEimaging. The combined uncertainty from all measurements was evaluated using statistical methods, and the resultant treatment accuracy was investigated for the ES.

Results:

Four sets of RCT measurements and 20 observations of associated digital probe showed SERCT of ±0·0186 mm and SEdigital probe of ±0·0002 mm. The mean positional shift of 0·2752 mm (σ = 0·0696 mm) was observed for 20 treatment settings of the phantom. The differences between radiological and predefined isocentres were 0·4650 and 0·4270 mm for two independent experiments. SEimaging and SEdiode  tool were evaluated as ±0·1055 and ±0·0096 mm, respectively. An expanded uncertainty of ±0·2371 mm (at 95% confidence level) was observed with our system.

Conclusions:

The combined result of the positional shift and expanded uncertainty showed close agreement with film investigations.

Frameless Fractionated Gamma Knife Radiosurgery with ICON™ for Large Metastatic Brain Tumors

BACKGROUND

Recently, a new generation of gamma knife radiosurgery (GKRS) equipped with a frameless immobilization system has encouraged the use of fractionated GKRS as an increasingly favorable treatment option. We investigated the preliminary outcome of efficacy and toxicity associated with frameless fractionated gamma knife radiosurgery (FF GKRS) for the treatment of large metastatic brain tumors.

METHODS

Fifteen patients with 17 lesions were treated using FF GKRS and included in this study, because of the large tumor size of more than 10 cm³. FF GKRS was performed based on a thermoplastic mask system for 3 to 5 consecutive days.

RESULTS

The mean duration of clinical follow-up was 12 months (range, 4-24), and the local control rate was 100%. Tumor volume decreased in 13 lesions (76.5%), and remained stable in 4 lesions (23.5%). One patient was classified as new lesion development because of the occurrence of leptomeningeal seeding regardless of the tumor volume change. Compared with the initial volume at the time of FF GKRS, tumor volume change at the last follow-up was 62.32% ± 29.80%. Cumulative survival rate at 12 months was 93.3% ± 6.4%. One patient died during the follow-up period because of the progression of the primary disease. No patient showed radiation necrosis on the follow-up images.

CONCLUSION

Daily FF GKRS by gamma knife ICON™ revealed satisfactory tumor control rate and low morbidity, despite the short follow-up period. Further prospective studies and a longer follow-up of a large cohort of patients diagnosed with brain metastases are required to elucidate the effect of FF GKRS in brain metastases.

Dosimetric characterization of hypofractionated Gamma Knife radiosurgery of large or complex brain tumors versus linear accelerator-based treatments

OBJECTIVE Noninvasive Gamma Knife (GK) platforms, such as the relocatable frame and on-board imaging, have enabled hypofractionated GK radiosurgery of large or complex brain lesions. This study aimed to characterize the dosimetric quality of such treatments against linear accelerator-based delivery systems that include the CyberKnife (CK) and volumetric modulated arc therapy (VMAT). METHODS Ten patients treated with VMAT at the authors' institution for large brain tumors (> 3 cm in maximum diameter) were selected for the study. The median prescription dose was 25 Gy (range 20-30 Gy) in 5 fractions. The median planning target volume (PTV) was 9.57 cm³ (range 1.94-24.81 cm³). Treatment planning was performed using Eclipse External Beam Planning V11 for VMAT on the Varian TrueBeam system, Multiplan V4.5 for the CyberKnife VSI System, and Leksell GammaPlan V10.2 for the Gamma Knife Perfexion system. The percentage of the PTV receiving at least the prescription dose was normalized to be identical across all platforms for individual cases. The prescription isodose value for the PTV, conformity index, Paddick gradient index, mean and maximum doses for organs at risk, and normal brain dose at variable isodose volumes ranging from the 5-Gy isodose volume (V5) to the 15-Gy isodose volume (V15) were compared for all of the cases. RESULTS The mean Paddick gradient index was 2.6 ± 0.2, 3.2 ± 0.5, and 4.3 ± 1.0 for GK, CK, and VMAT, respectively (p < 0.002). The mean V15 was 7.5 ± 3.7 cm³ (range 1.53-13.29 cm³), 9.8 ± 5.5 cm³ (range 2.07-18.45 cm³), and 16.1 ± 10.6 cm³ (range 3.58-36.53 cm³) for GK, CK, and VMAT, respectively (p ≤ 0.03, paired 2-tailed t-tests). However, the average conformity index was 1.18, 1.12, and 1.21 for GK, CK, and VMAT, respectively (p > 0.06). The average prescription isodose values were 52% (range 47%-69%), 60% (range 46%-68%), and 88% (range 70%-94%) for GK, CK, and VMAT, respectively, thus producing significant variations in dose hot spots among the 3 platforms. Furthermore, the mean V5 values for GK and CK were similar (p > 0.79) at 71.9 ± 36.2 cm³ and 73.3 ± 31.8 cm³, respectively, both of which were statistically lower (p < 0.01) than the mean V5 value of 124.6 ± 67.1 cm³ for VMAT. CONCLUSIONS Significantly better near-target normal brain sparing was noted for hypofractionated GK radiosurgery versus linear accelerator-based treatments. Such a result supports the use of a large number of isocenters or confocal beams for the benefit of normal tissue sparing in hypofractionated brain radiosurgery.

Tailored Treatment Options for Patients with Brain Metastases by a Relocatable Frame System with Gamma Knife Radiosurgery

OBJECTIVE

To report on our experience with the Elekta Extend system, a relocatable frame system used in patients with brain metastases for single-session, hypofractionated, or staged hypofractionated Gamma Knife radiosurgery (GKRS); and the evaluation of its efficacy.

METHODS

From March 2014 to September 2016, 856 patients with brain metastases underwent GKRS at our hospital. Of them, 35 patients who were retrospectively investigated, were selected for treatment with GKRS using the relocatable frame system. Individualized treatment strategy was chosen according to prior treatment history, number, size and location of tumor, or tumor harboring gene mutation.

RESULTS

Thirty-two (91.4%) patients underwent treatment with hypofractionated GKRS or staged hypofractionated GKRS, whereas 3 (8.6%) patients underwent single session GKRS. The mean radial setup difference from the reference measurements was 0.50 ± 0.16 mm. The median follow-up time after GKRS with the Extend system was 12 months (range, 1-45 months). The median overall survival time was 12 months (95% confidence interval 6.43-17.57). On multivariable analysis, performance status and extracranial metastases were independently prognostic factors for overall survival. Radiation necrosis developed in 4 cases (11.4%) during the follow-up period (2 with common terminology criteria for adverse events grade 2 and 2 with its grade 3).

CONCLUSIONS

The relocatable frame system can maintain submillimetric accuracy and provide tailored treatment option with reasonable tumor control and good survival benefits in selected patients with brain metastases. Especially, hypofractionated GKRS or staged hypofractionated GKRS with noninvasive frame is a safe and effective treatment option for large brain metastases or tumor adjacent to eloquent structures.

Fractionated Gamma Knife Radiosurgery as Initial Treatment for Large Skull Base Meningioma

We present our experience on the hypofractionated Gamma Knife radiosurgery (FGKS) for large skull base meningioma as an initial treatment. We retrospectively reviewed 23 patients with large skull base meningioma ≥10 cm³ who underwent FGKS as the initial treatment option. The mean volume of tumors prior to radiosurgery was 21.2±15.63 cm³ (range, 10.09~71.42). The median total margin dose and marginal dose per fraction were 18 Gy (range, 15~20) and 6 Gy (range, 5~6), respectively. Patients underwent three or four fractionations in consecutive days with the same Leksell® frame. The mean follow-up duration was 38 months (range, 17~78). There was no mortality. At the last follow-up, the tumor volume was stationary in 15 patients (65.2%) and had decreased in 8 patients (34.8%). Six patients who had cranial neuropathy at the time of FGKS showed improvement at the last clinical follow-up. Following FGKS, 4 patients (17%) had new cranial neuropathy. The trigeminal neuropathy was the most common and all were transient. The mean Karnofsky Performance Status score at pre-FGKS and the last clinical follow-up was 97.0±10.4 points (median, 100) and 98.6±6.9 (median, 100) points, respectively. FGKS has showed satisfactory tumor control with functional preservation for large skull base meningiomas. Further prospective studies of large cohorts with long term follow-up are required to clarify the efficacy in the tumor control and functional outcome as well as radiation toxicity.

Radiologic Response and Disease Control of Recurrent Intracranial Meningiomas Treated With Reirradiation

PURPOSE

To evaluate the clinical outcomes of reirradiation of recurrent meningiomas and factors related to patient selection and treatment modality.

METHODS AND MATERIALS

Recurrent meningioma patients who failed prior stereotactic radiosurgery (SRS) or fractionated external beam radiation therapy (EBRT) received reirradiation using either SRS or EBRT. Complete response (CR), partial response (PR), and progression after reirradiation were evaluated using the MacDonald criteria. Local control (LC), progression-free survival (PFS), and overall survival (OS) after reirradiation were analyzed using the Kaplan-Meier method. Logistic and Cox regression analyses were performed to identify factors associated with reirradiation modality and PFS, respectively.

RESULTS

Forty-three patients (14 grade 1/unknown, 29 grade 2/3) were reirradiated with SRS (67%) or EBRT (33%). Median time from initial SRS/EBRT to reirradiation was 60 months (range, 7.5-202); median tumor volume at the time of reirradiation was 4.8 cm³ (range, 0.14-64). After a median radiologic follow-up of 19.4 months, the response rate (CR + PR) was 8% for grade 1 and 20% for grade 2/3 meningiomas. After 2 years, LC was 78%, PFS was 63%, and OS was 80%. Larger tumor volume and prior SRS were associated with reirradiation using EBRT. Reirradiated grade 2/3 meningiomas had significantly worse PFS than grade 1 (2-year PFS: 50% vs 92%, respectively; P = .02) but not LC (P = .11) or OS (P = .39). On multivariable analysis, worse PFS was significantly associated with grade 2/3 histology (hazard ratio, 3.92; 95% confidence interval, 1.33-11.6) as well as worse Karnofsky Performance Scale score but not reirradiation dose, volume, and modality. Grades 3 to 4 radiation necrosis developed in 4 patients (10%).

CONCLUSIONS

Reirradiation of recurrent meningiomas appears to be feasible with promising clinical outcomes and an acceptable toxicity profile.

Emerging Indications for Fractionated Gamma Knife Radiosurgery

BACKGROUND

Gamma Knife radiosurgery (GKRS) allows for the treatment of intracranial tumors with a high degree of dose conformality and precision. There are, however, certain situations wherein the dose conformality of GKRS is desired, but single session treatment is contraindicated. In these situations, a traditional pin-based GKRS head frame cannot be used, as it precludes fractionated treatment.

OBJECTIVE

To report our experience in treating patients with fractionated GKRS using a relocatable, noninvasive immobilization system.

METHODS

Patients were considered candidates for fractionated GKRS if they had one or more of the following indications: a benign tumor >10 cc in volume or abutting the optic pathway, a vestibular schwannoma with the intent of hearing preservation, or a tumor previously irradiated with single fraction GKRS. The immobilization device used for all patients was the Extend system (Leksell Gamma Knife Perfexion, Elekta, Kungstensgatan, Stockholm).

RESULTS

We identified 34 patients treated with fractionated GKRS between August 2013 and February 2015. There were a total of 37 tumors treated including 15 meningiomas, 11 pituitary adenomas, 6 brain metastases, 4 vestibular schwannomas, and 1 hemangioma. At last follow-up, all 21 patients treated for perioptic tumors had stable or improved vision and all 4 patients treated for vestibular schwannoma maintained serviceable hearing. No severe adverse events were reported.

CONCLUSION

Fractionated GKRS was well-tolerated in the treatment of large meningiomas, perioptic tumors, vestibular schwannomas with intent of hearing preservation, and in reirradiation of previously treated tumors.

Clinical Positioning Accuracy for Multisession Stereotactic Radiotherapy With the Gamma Knife Perfexion

Multisession stereotactic radiation therapy is increasingly being seen as a preferred option for intracranial diseases in close proximity to critical structures and for larger target volumes. The objective of this study is to investigate the reproducibility of the Extend system from Elekta. A retrospective review was conducted for all patients treated with multisession Gamma Knife between July 2010 and June 2015, including both malignant and benign lesions. Eighty-four patients were treated in this 5-year span. The average residual daily setup uncertainty was 0.48 (0.19) mm. We compare measurements of setup uncertainty from the Extend system to measurements performed with a linac-based approach previously used in our center. The Extend system has significantly reduced setup uncertainty for fractionated intracranial treatments at our institution. Positive results were observed in a small population of edentulous patients. The Extend system compares favorably with other approaches to delivering intracranial stereotactic radiotherapy and is a robust, simple-to-use, and precise method for treating multisession intracranial lesions.

Radiosurgery for Pediatric Brain Tumors

The utility of radiosurgery for pediatric brain tumors is not well known. For children, radiosurgery may have an important role for treating unresectable tumors, residual disease, or tumors in the recurrent setting that have received prior radiotherapy. The available evidence demonstrates utility for some children with primary brain tumors resulting in good local control. Radiosurgery can be considered for limited residual disease or focal recurrences. However, the potential toxicities are unique and not insignificant. Therefore, prospective studies need to be performed to develop guidelines for indications and treatment for children and reduce toxicity in this population.