Polarized Cherenkov light imaging dosimetry: the impact of source to detector distance

Objective.With every treatment vault being different, the impact of geometrical parameters such as the signal source-to-camera distance on dose proportionality must be evaluated. The aim of this study is to characterize the Cherenkov signal and polarization state as a function of the source-to-camera distance. Our hypothesis is that with increasing distance, the need for angular correction distributions decreases, resulting in acquisition of a polarized Cherenkov signal directly proportional to dose.Approach.A water tank and a polyvinyltoluene-based plastic scintillator volume were irradiated by a 6 MV beam to respectively produce Cherenkov emissions as well as a control signal. Monte Carlo reference simulations were performed using TOPAS. Acquisitions of the Cherenkov signal were achieved using a cooled CCD camera and a time-gated intensified CMOS camera. By fitting a modified Malus Law to the Cherenkov acquisitions, the total Cherenkov signal intensity and its purely polarized component was extracted. Signal source-to-camera distance of 0.5, 1, 2, 3 and 4 m were tested to evaluate this distance's impact on the signal distributions. Projected percent depth dose (PPDD) and projected transverse profiles calculated from the different signal sources were then compared.Main results.All PPDDs at camera distances of 3 and 4 m agree with Monte Carlo (⩽5%) over depths ranging from 1.5 to 16 cm. Cherenkov PPDDs at camera distances of 0.5 and 1 m show significant discrepancies (⩾5%) compared to MC because no angular corrections are applied. Over the plateau region of projected transverse profiles, general agreement with MC is achieved. Thirteen of the 17 luminescence-based beam widths show⩽5% differences with MC.Significance.This study confirms the above-mentioned hypothesis up until the image quality diminishes. For this work's setup, the optimal camera distance for dosimetry using Cherenkov polarized imaging was found to be between 3 and 4 m.