ESTRO 2024 - Abstract Book

S3279

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

average gray value/dose within a region of interest in the center of the field and dosimeter. The response of the dosimeter was normalized by the reference dose.

Results:

The variation of the normalized response with dose varying from 3.6 to 12.6 Gy is within 3% for both dosimetric systems, within the facility, allowing linear calibration of both systems. The response per Gray, hence calibration factor, in Antwerp is 15.9% lower compared to Orsay while the setup was reproduced as good as possible. This is most probably due to the difference in phantom as the Cherenkov light generated in the PMMA phantom contaminates the scintillating signal. No dose rate dependence was observed for dose rates up to 140 Gy/s. Neither with variation of the pulse length, nor with variation of the PRF. The normalized response with dose rate was within 2.5% for both dosimetric systems, irrespective of the facility. The profiles of the tested and reference dosimeters can be appreciated in the figure below. High overlap between the three dosimeters is observed in the field, but the penumbra of the radiochromic film is with 9.5 mm wider than for the OSL and 2D scintillating sheet, which have penumbrae of respectively 8.7 mm and 8.8 mm. This suggests that radiochromic film might not be the most suitable for 2D UHDR dosimetry, and that the OSL system is preferred. The outliers for radiochromic film and the OSL system need further investigation. The 2D scintillating system was capable of dose assessment for individual pulses. Due to the absence of triggering, 2.8% of the pulses were not detected or underestimated. Triggered camera acquisition is currently under investigation and is expected to increase the reproducibility. No energy dependence was concluded for the 2D scintillating system, with differences of 1.7% and 0.6% in normalized response between 7 and 9 MeV, and 5 and 7 MeV, respectively.

Conclusion: