30. Monte Carlo modeling Varian TrueBeam Novalis STX linear accelerator and methods of validation

• Published in: Physica medica Vol. 44; pp. 40 - 41
• Main Authors: Akunzi, J., Leni, P.E., Gschwind, R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2017
• ISSN: 1120-1797; 1724-191X
• DOI: 10.1016/j.ejmp.2017.10.110

In order to safely administrated highly complexes radiotherapy technics like VMAT or IMRT, the implementation of a quality assurance software is in progress at Chrono-environnement UMR CNRS 6249 laboratory based in Franche-Comté (France). The Monte Carlo modeling of the TrueBeam Novalis STx used in Montbéliard hospital was performed. Hereafter, the validation for clinic use of IAEA-compliant phase-space files for 10X, and 10XFFF. These phase-space files were calculated by the Varian Monte Carlo research team. The modeling of TrueBeam Novalis STX of Varian was implemented using the Monte Carlo code BEAMnrc/DOSXYZnrc. In order to validate the modeling, the simulations of the phase-space files for the 10 MV beams in both flattened and unflattened (FFF) mode were performed. BEAMnrc was used to create field specific phase spaces under the jaws for field ranging from 3 cm ∗ 3 cm to 20 cm ∗ 20 cm. DOSXYZnrc was used to calculate doses in water phantom. Calculated cross-lines profiles, percent depth doses (PDD) and output factors were compared with measurements provided by Montbéliard hospital. The γ-index test was performed on both PDDs and cross-lines profiles. For cross-line profiles, agreements in the 80%–20% width and in the 50% field size were better than 2 mm for all fields. More over agreement better than 1.5%, 1 mm and 2%, 2 mm were found for 10 MV FFF and 10 MV, respectively. Calculated and measured percent depth doses beyond the buildup region agreed within 1:5%, 1 mm for 10 MV FFF beams and within 2%, 2 mm for 10 MV beams. The agreement between calculate and measured output factors for all field were within 1%. The X10 and X10 FFF Varian phase-spaces files have been validated in homogeneous medium. The perspectives of this study include the validation of the modeling in a heterogeneous medium and then a comparison of Monte Carlo VMAT treatment with a TPS one.