Leksell model g frame

Single-session GKRS was performed using Gamma Knife unit models U, C, Perfexion, and Icon (Elekta AB). The first Leksell Gamma Unit at the University of Virginia was installed in March 1989. Leksell Gamma Knife model C was installed in 2001, Perfexion in 2007, and Icon in 2016. Radiosurgical techniques have been described in detail previously. 19 In brief, SRS was performed with frame-based stereotaxy using the Leksell Model G frame (Elekta AB); the patient was placed under local anesthesia with conscious sedation. Initially, stereotactic CT scanning was used for treatment planning, but around the year 2000, high-resolution MRI became the standard of care. Currently, radiosurgical imaging typically includes highresolution 1-mm-thick pre-and postcontrast T1-weighted 3-T MRI scans. GKRS dose planning was performed by a multidisciplinary team that included a neurosurgeon, radiation oncologist, and medical physicist. Planning was tailored toward individual patient needs and imaging findings; however, the maximal radiation dose to the optic nerve, chiasms, and tracts was generally kept below 8 to 12 Gy. Radiosurgical parameters, including the margin and maximum dose, optic apparatus maximal dose, the isodose line, the tumor volume, and the number of isocenters were recorded in all cases.

A stereotactic coordinate frame (Leksell Model G frame; Elekta Instruments AB) was applied under local anesthesia, supplemented with mild sedation in some cases. For target coordinate determination and dose planning, stereotactic Gd-enhanced T1-weighted axial MR images with a slice thickness of 2 mm, multiple slices of which covered the entire brain, were obtained. For dose planning, the Leksell GammaPlan (Elekta) was used. GK SRS was performed using a Leksell GK Model B unit (Elekta) from July of 1991 through June of 2003, a Leksell GK Model C unit (Elekta) from July of 2003 through November of 2013, and thereafter, a Leksell GK Perfexion (Elekta) through June of 2016. Standard, single-session GK SRS was performed. However, in 35 patients (3.8%) in whom the tumor volume was large, a 3-stage treatment was applied. 3 Our dose selection was based on our experiences accumulated during the 7-year period between 1992 and 1998 in Japan. The median dose at the tumor periphery was 22.00 (interquartile range [IQR] 20.00-24.00, maximum 25.00) Gy. In this series, peripheral doses of 15.00-25.00 Gy were used in more than 99% of patients. Radiosurgical parameters are summarized in Table 2. The mean/median CIs were 0.62/0.66 (IQR 0.53-0.74, range 0.08-0.88) and the mean/median GIs were 3.20/3.09 (IQR 2.83-3.39, range 2.27-11.4).

Baseline patient data included patient characteristics, AVM features, and SRS treatment parameters. Eloquent locations included the sensorimotor, language, and visual cortex, hypothalamus and thalamus, internal capsule, brainstem, cerebellar peduncles, and deep cerebellar nuclei. 24 Deep locations included the thalamus, basal ganglia, and brainstem. 28 The Spetzler-Martin (SM) grade, modified radiosurgery-based AVM score, and Virginia Radiosurgery AVM Scale score were calculated for each AVM. 24, 27, 28 SRS was performed using the Gamma Knife, and the specific model used varied by year and availability at each institution. The SRS technique for AVMs has been previously described. 30 In brief, the patient's calvaria was affixed within a Leksell model G frame (Elekta AB) under anesthesia. The nidal angioarchitecture and spatial anatomy of the AVM were delineated on DSA and thin-slice (slice thickness 1-2 mm) contrast-enhanced MRI or on CTA when MRI was contraindicated.