Cherenkov emission dosimetry for electron beam radiotherapy: A monte carlo feasibility study of absolute dose prediction

Abstract

Current electron beam dosimeters face two major challenges. They are not water/tissue equivalent, and therefore require conversion to dose to water/tissue. Moreover, they must be placed in the radiation beam, which results in beam perturbation and dose averaging. These challenges limit their spatial resolution for intensity-modulated delivery or in vivo dosimetry. Yet, Cherenkov radiation by high-energy charged particles is emitted in water and in tissue, can be detected outside the beam, and is inherent to all high-energy radiotherapy beams. Despite these advantages, Cherenkov emission has yet to be implemented for clinical dosimetry. The work presented here investigates via first-principles derivation and Monte Carlo simulation the feasibility of absolute Cherenkov dosimetry for electron beam radiotherapy. A quantitative model for predicting absolute dose from Cherenkov intensity in a phantom was derived from first principles for highenergy charged particles of known incident energy with the assumption that all collisional energy loss is absorbed and all radiative energy loss escapes. The model was validated via simulation of 260 keV - 18 MeV electrons incident on water. Monte Carlo simulations were carried out in Geant 4. The absolute Cherenkov dosimetry model presented here was able to predict absolute dose from Cherenkov intensity to within a clinically viable uncertainty of less than 3%.