Monte Carlo modeling and phantom studies show Cherenkov emission per unit dose during total skin electron therapy is...

Cherenkov imaging provides a noninvasive approach to visualize total skin electron therapy (TSET) radiation dose deposition on patient. Accurate conversion of Cherenkov intensity to radiation dose is necessary for in vivo dosimetry to assess the spatial dose distribution in TSET. Studies have shown a linear correlation between Cherenkov intensity and absorbed dose, but the effect of tissue optical properties on the Cherenkov emission per dose is not well understood.

This work uses Monte Carlo simulations and experiments to assess how tissue optical properties affect the Cherenkov emission per dose detected during TSET.

Monte Carlo modeling was used to simulate Cherenkov generation during total skin electron therapy and quantify the effect of tissue optical properties on the detected Cherenkov emission. The study examined a clinically relevant range of absorption coefficients (0.01-1 cm^-1) and reduced scattering coefficients (2-40 cm^-1) at 665 nm. The effect of tissue optical properties, depth of origin and the angular distribution of Cherenkov emission on tissue surface were systematically evaluated. The Monte Carlo results are compared to measurements for a series of solid phantoms. An analytical function is proposed to fit the optical properties dependence (µ_a and µ_s') of Cherenkov emission for tissue.

Simulation results show that Cherenkov emission decreases with increasing tissue absorption and effective attenuation coefficients but increases then decreases with tissue scattering coefficients. 80% of the surface-detected emission originated from superficial layers 0.17- 2.0 cm beneath the surface. Angle-specific generation of Cherenkov radiation in tissue has not resulted in preferential exiting angle as the propagation directions of most Cherenkov photons are randomized prior to reaching the surface. Monte Carlo simulation (max dev 0.23%) agrees with experiments to within a standard (maximum) % deviation of 2.8% (7.6%).

Our findings indicate that tissue optical properties exert a substantial influence on the surface Cherenkov emission. The optical properties dependence of Cherenkov emission per dose can be expressed as a two-dimensional function of µ_a and µ_s'. An analytical expression is presented. Monte Carlo simulation agrees with experiments for TSE electrons used in a series of tissue simulating phantoms.