GPU-Accelerated Optical Simulation of Cherenkov Emission Under Different Beam Conditions
Abstract
Purpose
Cherenkov imaging is a promising technique for visualizing and quantifying surface dose in radiation therapy. However, the absolute relationship between surface dose and emitted Cherenkov photons remains uncertain and varies with beam and tissue conditions. This study aims to systematically investigate the effects of beam conditions on Cherenkov emission using a GPU-accelerated Monte Carlo optical propagation code.
Methods
An in-house GPU-accelerated Monte Carlo optical simulation framework was developed using CUDA to model Cherenkov photon generation and transport. Initial Cherenkov photons were generated from electron phase-space data scored in TOPAS. The optical photon propagation in tissue was simulated using wavelength-dependent absorption and scattering coefficients, an anisotropy factor of 0.9, and a refractive index of 1.4. The framework was validated using silicone-based house-made optical phantoms with tunable optical properties achieved by varying concentrations of carbon and TiO2. Phantoms were irradiated using clinically relevant beam configurations, including 6 MV photon beams (TrueBeam 6X, 6XFFF, and Halcyon 6XFFF) and 6 MeV electron beams (TrueBeam 6e). Measured Cherenkov signals were compared with Monte Carlo simulations using matched beam phase-space data and corresponding tissue optical properties.
Results
Simulation results showed good agreement with experimental measurements across nine optical phantoms (MAE: 7.2% for 6 MeV electrons and 10.9% for TrueBeam 6 MV photons). Differences in superficial electron distributions between beam types directly led to distinct dose-to-Cherenkov responses. The effects of beam angular dependence and effective sampling depth on surface Cherenkov emission will be further quantified and evaluated.
Conclusion
A GPU-accelerated Monte Carlo optical model was developed and experimentally validated to characterize Cherenkov emission from clinical beams, providing a direct framework for understanding beam-dependent Cherenkov emission and optical property dependence through analysis of near-surface primary and secondary electron distributions.