title: Dosimetric characterization of hypofractionated Gamma Knife radiosurgery of large or complex brain tumors versus linear accelerator-based treatments.
abstract: 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 cm3and 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 cm3for 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.
authors.affiliation: Departments of 1 Radiation Oncology and.|Department of Radiation Oncology, Stanford University, Stanford, California; and.
authors.forename: Peng
authors.initials: P
authors.lastname: Dong
authors.affiliation: Departments of 1 Radiation Oncology and.
authors.forename: Angélica
authors.initials: A
authors.lastname: Pérez-Andújar
authors.affiliation: Department of Radiation Oncology, The University of Arizona School of Medicine and St. Joseph's Hospital and Medical Center, Phoenix, Arizona.
authors.forename: Dilini
authors.initials: D
authors.lastname: Pinnaduwage
authors.affiliation: Departments of 1 Radiation Oncology and.
authors.forename: Steve
authors.initials: S
authors.lastname: Braunstein
authors.affiliation: Neurosurgery, University of California, San Francisco.
authors.forename: Philip
authors.initials: P
authors.lastname: Theodosopoulos
authors.affiliation: Neurosurgery, University of California, San Francisco.
authors.forename: Michael
authors.initials: M
authors.lastname: McDermott
authors.affiliation: Departments of 1 Radiation Oncology and.
authors.forename: Penny
authors.initials: P
authors.lastname: Sneed
authors.affiliation: Departments of 1 Radiation Oncology and.
authors.forename: Lijun
authors.initials: L
authors.lastname: Ma
mesh_terms: D001932:Brain Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D000069473:Radiation Dose Hypofractionation; D016634:Radiosurgery / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D047368:Tumor Burden
keywords: CI = conformity index; CK = CyberKnife; CyberKnife; GI = gradient index; GK = Gamma Knife; Gamma Knife; LINAC = linear accelerator; PTV = planning target volume; V10 = 10-Gy isodose volume; V15 = 15-Gy isodose volume; V5 = 5-Gy isodose volume; VMAT = volumetric modulated arc therapy; f-IMRT = fan beam–based intensity modulated radiotherapy; hypofractionation; normal tissue; oncology; stereotactic radiosurgery; volumetric modulated arc therapy