ESTRO 2022 - Abstract Book

S98

Abstract book

ESTRO 2022

four polarization axis (0°, 45°, 90°, 135°), as presented on figure 1. The polarized component of the signal is extracted using Malus law. This polarized portion should be proportional to the dose, given a correction factor that can be defined by Cherenkov polar and azimuthal angular distributions. Hence, Cherenkov emission was simulated using the Geant4 toolkit (v4.10.04). Monte Carlo angular distributions were then used to correct polarized measurements. The resulting images consist of 2D projections as the signal is summed along the camera’s optical axis. Projected percent depth dose (PPDD) and profiles were extracted for each measurement and compared to equivalent dosimetric film measurements.

Results Cherenkov emission generated from electron beams exhibited a strong polar dependence, peaked at 41°, with a distribution that varied with depth. This resulted in large dose discrepancies (up to 60%) using the raw Cherenkov emission for dose measurements. Overall, 42 ± 4% (6 MeV) and 47 ± 3% of the signal was found to be linearly polarized. After applying a polarization correction, PPDD presented differences (mean ± standard deviation) with film measurements of − 1 ± 2% (6 MeV) and 0.9 ± 2% (18 MeV). For projected profiles, differences of 0.9 ± 0.6% (6 MeV) and 0.8 ± 0.6% (18 MeV) between films and polarized corrected signals are obtained on the beam central axis. Figure 2 summarizes the dose measurement results.

Conclusion The results suggest that accurate, perturbation-free in water dose measurement can be achieved using Cherenkov radiation combined with polarization imaging. Since the correction function is based on angular distributions, which are not directly related to the dose, the method is expected to be less prone to redundancy errors than previously proposed Monte Carlo based correction methods.

OC-0123 Characterization of small active detectors for electronic brachytherapy dosimetry

F. Garcia Yip 1 , T. Schneider 1 , M. Reginatto 2 , R. Behrens 1 , L. Buermann 3 , F. Grote 1

1 Physikalisch-Technische Bundesanstalt (PTB), 6.3 Radiation Protection Dosimetry, Braunschweig, Germany; 2 Physikalisch- Technische Bundesanstalt (PTB), 6.4 Neutron radiation, Braunschweig, Germany; 3 Physikalisch-Technische Bundesanstalt (PTB), 6.2 Dosimetry for radiation therapy and diagnostic radiology, Braunschweig, Germany