196. Preliminary comparison between two different stereotactic machines, robot based and linac based, by means of a 3D phantom. (December 2018)

• Record Type: Journal Article
• Authors: Reyes Ramos, A.K.; Strigari, L.; D'Andrea, M.; Iaccarino, G.; Borzì, G.R.; Candiano, G.; Franza, N.
• Is Part Of: Physica medica. Volume 56(2018)Supplement 2
• Page Start: 182
• Publication Date: 2018-12
• Subjects: Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2018.04.207
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract : Purpose: Two machines, Accuray Cyberknife and Varian linac TrueBeam Novalis STx, equipped with 6MV Flattering Filter Free (FFF) and stereotactic cones were used to compare similar plans on a 3D phantom in order to evaluate differences in the dose distributions. Moreover, this work aims to investigate the possibility to use with Cyberknife the same 3D phantom correction factors already applied with conventional linacs setup. Methods: Analysis was carried out with Scandidos Delta4 Phantom Plus (1069 p diodes types with 0.78 mm 2 active area) on which a Cyberknife plan and a TrueBeam plan with identical ballistics were superimposed for a series of measurements of narrow beams. The setup, originally selected from Cyberknife, was converted into linac coordinates (gantry and couch angles) with the same cone size. The plan for the TrueBeam was calculated and delivered using two energies, 6MV and 6MV FFF. Results: First, measurements were carried out on TrueBeam with separate dose fields, in order to evaluate the feasibility of narrow beams to be intercepted by diodes arrays in the phantom with different phantom tilt setups (0°, −4°), obtaining these gamma values: 99.0% with 6 MV, 98.8% with 6 MV FFF (local gamma, 2%-2 mm, threshold 20%). Then the delivered doses were compared obtaining a gamma value of 82.1% for 6 MV and 84.1% for 6 MV FFF. Conclusion: The two machines were similar in terms of dose fall (with a steeper gradient for Cyberknife), dose coverage of target and in general clinical acceptance of the plans. The 3D phantom was initially used on both machines with the same correction factors and it was able to detect dose differences when properly irradiated with beams with a no-parallel incidence on plates (4° was enough in the setup, varying agreement for the same plan from 83% gamma value to 99%).