Accurate Dose Measurements Using Cherenkov Polarization Imaging

TL;DR

This paper introduces a polarization imaging technique for Cherenkov radiation that significantly improves the accuracy of in-water dose measurements in radiotherapy by correcting anisotropy effects.

Contribution

It presents a novel polarization-based method that corrects Cherenkov anisotropy, achieving high-precision dose measurements in water-based phantoms.

Findings

Corrected polarized signals reduced depth deviation from 20% to 0.8%.

Dose profile differences from TPS predictions are within 3-8%.

Approximately 29% of Cherenkov signal was polarized.

Abstract

Purpose: Cherenkov radiation carries the potential of direct in-water dose measurements, but its precision is currently limited by a strong anisotropy. Taking advantage of polarization imaging, this work proposes a new approach for high accuracy Cherenkov dose measurements. Methods: Cherenkov produced in a 15x15x20 cm^3 water tank is imaged with a cooled CCD camera from four polarizer transmission axes [0{\deg}, 45{\deg}, 90{\deg}, 135{\deg}]. The water tank is positioned at the isocenter of a 5x5 cm^2, 6 MV photon beam. Using Malus' law, the polarized portion of the signal is extracted. Corrections are applied to the polarized signal following azimuthal and polar Cherenkov angular distributions extracted from Monte Carlo simulations. Percent depth dose and beam profiles are measured and compared with the prediction from a treatment planning system (TPS). Results: Corrected polarized signals on the central axis reduced deviations at depth from 20% to 0.8\pm1%. For the profile measurement, differences between the corrected polarized signal and the TPS calculations are 1\pm3% and 8\pm3% on the central axis and penumbra regions respectively. 29\pm1% of the Cherenkov signal was found to be polarized. Conclusions: This work proposes a novel polarization imaging approach enabling high precision water-based Cherenkov dose measurements. The method allows correction of the Cherenkov anisotropy within 3% on the beam central axis and in depth.