title: Dosimetric verification of stereotactic radiosurgery/stereotactic radiotherapy dose distributions using Gafchromic EBT3.
abstract: Aim of this study is to examine the feasibility of using the new Gafchromic EBT3 film in a high-dose stereotactic radiosurgery and radiotherapy quality assurance procedure. Owing to the reduced dimensions of the involved lesions, the feasibility of scanning plan verification films on the scanner plate area with the best uniformity rather than using a correction mask was evaluated. For this purpose, signal values dispersion and reproducibility of film scans were investigated. Uniformity was then quantified in the selected area and was found to be within 1.5% for doses up to 8 Gy. A high-dose threshold level for analyses using this procedure was established evaluating the sensitivity of the irradiated films. Sensitivity was found to be of the order of centiGray for doses up to 6.2 Gy and decreasing for higher doses. The obtained results were used to implement a procedure comparing dose distributions delivered with a CyberKnife system to planned ones. The procedure was validated through single beam irradiation on a Gafchromic film. The agreement between dose distributions was then evaluated for 13 patients (brain lesions, 5 Gy/die prescription isodose ~80%) using gamma analysis. Results obtained using Gamma test criteria of 5%/1 mm show a pass rate of 94.3%. Gamma frequency parameters calculation for EBT3 films showed to strongly depend on subtraction of unexposed film pixel values from irradiated ones. In the framework of the described dosimetric procedure, EBT3 films proved to be effective in the verification of high doses delivered to lesions with complex shapes and adjacent to organs at risk.
authors: School of Medical Physics, University of Milan, Milan, Italy. Electronic address: davide.cusumano@unimi.it.
authors: Davide
authors: D
authors: Cusumano
authors: Health Department, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy.
authors: Maria L
authors: ML
authors: Fumagalli
authors: Department of Neurosurgery, Radiotherapy Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy.
authors: Marcello
authors: M
authors: Marchetti
authors: Department of Neurosurgery, Radiotherapy Unit, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy.
authors: Laura
authors: L
authors: Fariselli
authors: Health Department, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy.
authors: Elena
authors: E
authors: De Martin
mesh_terms: D001932:Brain Neoplasms / Q000601:surgery*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D005373:Film Dosimetry / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
keywords: Dosimetric verification; Gafchromic EBT3; High dose; Stereotactic radiosurgery/radiotherapy