Establishment and validation of a FLUKA radiation model for a medical electron linear accelerator room based on a virtual source.

PURPOSE: In Monte Carlo (MC) simulations of medical electron linear accelerator (linac) rooms using FLUKA, time-consuming modeling and simulation of the accelerator head are typically required, and FLUKA cannot directly read the phase space files (PSF) for accelerator heads provided by the IAEA. To address this, this study aimed to establish and validate the accuracy of a radiation model for an accelerator room within FLUKA using a virtual source, thereby enhancing the applicability of FLUKA for the design and evaluation of rooms housing different medical electron linacs.

METHODS

The 6 MV photon beam from a Varian 23EX linac was modeled as consisting of primary photons, scattered photons, and contaminant electrons. Their energy spectra and spatial distributions were represented by mathematical formulas. Python code was used to sample particle information (type, position, direction, energy, weight) from this mathematically defined virtual source, generating a FLUKA-readable PSF. A room radiation model was then established in FLUKA. Its accuracy was validated by comparing simulated and measured percentage depth dose (PDD) and off-axis ratios (OAR) in a water tank, as well as comparing simulated and measured dose equivalent rates at selected points inside the accelerator room.

RESULTS

The deviation between simulated and measured PDD was within 1%, and that for the OAR was within 2%. At gantry angles of 0° and 90° (with the head oriented toward the maze inner entrance), the simulated dose-equivalent rates at the points of interest inside the treatment room closely agreed with the measured values.

CONCLUSION

The phase-space file sampled from the virtual source can faithfully reproduce the beam characteristics in FLUKA. The agreement between simulation and measurement at the points of interest demonstrates that the room radiation model established in FLUKA using the virtual source accurately reflects the actual radiation field in the treatment room. This approach replaces the need for simulating the accelerator head model and improves the efficiency of using FLUKA for radiation protection studies on rooms equipped with different medical electron linear accelerators.