A Deconvolution Formulation for Cerenkov Light Dosimetry in Radiation Therapy

Abstract

Cerenkov light is the visible optical emission of photons that are created by the passage of high-energy charged particles in a dielectric medium. Since its discovery in 1934, Cerenkov light has been paramount to applications of high-energy radiation research. Recently, there has been considerable interest in imaging Cerenkov light during external beam radiation therapy as a means to perform in-vivo dose measurement. However, the exact relationship between Cerenkov light emission and dose deposition is not well characterized. In this thesis, the relationship between radiation beam fluence, dose deposition, and Cerenkov light emission is derived in an integral equation, describing the convolution relationships that exist between these physical parameters. This set of equations contained a convolution kernel called the Cerenkov scatter function (CSF). The CSF was solved with Monte Carlo techniques using the Geant4 architecture for medically-oriented simulations (GAMOS) to simulate radiation-induced optical emissions in an optical phantom and human skin tissue model. The theoretical formulation was experimentally evaluated using an optical phantom irradiated by high-energy photon beams. Next, the limitations and dependence of theoretical formulation were tested through a perturbation analysis performed on the CSF through Monte Carlo simulation. Lastly, the theoretical formulation was extended to clinically-relevant geometries, including curved surfaces, by breaking the limitation of space-invariance of the CSF. The theoretical formulation was found to improve the light-to-dose correspondence in Cerenkov light images, particularly in high dose gradient regions, and has the potential to improve the methods of Cerenkov imaging arising within radiation oncology. Based upon these results, it is expected that the theoretical formulation may be extended for use in a new Cerenkov imaging system which couples patient geometry imaging and measurement of Cerenkov light in-vivo.