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Validation of Monte Carlo simulation of 6 MV photon beam delivered by the Vero4DRT linear accelerator using BEAMnrc and DOSXYZnrc

University of British Columbia

The goal of this project is to develop a Monte Carlo (MC) simulation model for the 6MV Vero4DRT platform which is a stereotactic ablative radiation therapy (SABR) medical linear accelerator. This MC model can simulate a variety of radiotherapy delivery techniques, including three-dimensional conformal radiotherapy (3DCRT), dynamic conformal arc (DCA) therapy, as well as complex treatments such as static-field step-and-shoot intensity modulated radiotherapy (sIMRT), volumetric modulated arc therapy (VMAT) and non-coplanar trajectory-based Dynamic Wave Arc (DWA) in a single MC run. Open-source Monte Carlo applications based on EGSnrc particle transport codes are used to simulate the medical linear accelerator head components (BEAMnrc). The VERO4DRT has a maximum radiation field size of 15×15 cm² at 100 cm from the source. All beam shaping is achieved with a low-transmission multileaf collimator (MLC). The moving MLC leaves are modelled using the SYNCVMLC component module in BEAMnrc. Radiation doses to patients and phantoms are simulated using DOSXYZnrc codes. Electron energy tuning is achieved by comparing measured vs simulated percentage depth doses (PDDs) for a variety of field sizes in a water phantom. Electron spot size tuning is achieved by comparing beam profiles at depths 1.5 and 10 cm for the same field sizes. MC simulations with electron beam energy of 5.9 MeV and spot size FWHM=1.9mm demonstrated the closest agreement with measurement. The differences between measurement and calculation are <2.0% for the descending part of PDDs. The differences in beam profiles are <2.1% in all low dose gradient regions. Treatment plans are generated using the RayStation (RaySearch) treatment planning system (TPS). MC simulations of dose are performed on voxelized (2.5 mm³) patient CT datasets. Planning-target-volume (PTV) and organs-at-risk (OAR) dose-volume histograms (DVH) are compared to TPS calculated doses. Radiotherapy beam deliveries for 3DCRT, DCA, sIMRT, VMAT and DWA simulated on patient CT datasets result in dose distributions having acceptable DVH agreement with TPS calculated doses. The Vero4DRT accelerator was successfully modelled using MC simulations. This MC model can be used as an independent dose calculation and quality assurance tool for complex radiotherapy treatment plans generated by the RayStation TPS.

Text

2020-08-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/71463

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/