Author: Baozhu Lu, Timothy C. Zhu, Yifeng Zhu π¨βπ¬
Affiliation: University of Pennsylvania π
Purpose: Cherenkov intensity can be quantitatively correlated to surface dose but need certain corrections for accurate dose measurements. This study aims to investigate the impact of incident beam angles, camera viewing angles, and surface curvature on Cherenkov emissions from the patientβs body during total skin electron therapy.
Methods: Monte Carlo simulations were conducted to model Cherenkov emission spectra (400β1000 nm) using a clinically relevant range of tissue optical properties (absorption coefficient ΞΌβ = 0.1β1 cmβ»ΒΉ; reduced scattering coefficient ΞΌβ' = 5β40 cmβ»ΒΉ at 665 nm). Initial Cherenkov photon distributions were sampled from electron phase spaces generated in TOPAS, a Geant4-based Monte Carlo code for electron transport. An in-house code simulated photon propagation in a semi-infinite medium (with different surface curvature) using different optical properties, an anisotropy factor of 0.9, and a refractive index mismatch of 1.4. The absorption and reduced scattering coefficient spectrum were derived from: (1) the spectra of oxy- and deoxyhemoglobin to emulate human tissue, and (2) measured spectra of optical phantoms, which are mixtures of carbon and TiO2. The escaping photons were recorded and compared to the experiment results.
Results: Simulation results show good agreement ( within 6.3% deviation) with experimental measurements of phantoms with different optical properties. Tissue optical properties dependence of Cherenkov emission can be expressed in function of tissue optical properties. The angular distribution of Cherenkov emission and the depth of origin of the escaping Cherenkov photons are further evaluated.
Conclusion: A Monte Carlo framework is developed to simulate Cherenkov emission under different conditions and validated against the experiments. The corrections factors in the Cherenkov-to-dose conversion, accounting for the beam incident angles and camera viewing angles, will be determined, enhancing the accuracy of dose quantification in clinical applications.