Author: Dominique Guillet, Arthur Lalonde, Bryan R. Muir, James Renaud, Karim Zerouali 👨🔬
Affiliation: Universite de Montreal, Centre Hospitalier de l'Universite de Montreal, National Research Council 🌍
Purpose:
To evaluate the dose rate dependence, beam quality dependence, and short-term stability of a novel flashDiamond (fD) prototype detector for conventional and ultra-high dose rate (UHDR) beams
Methods:
The fD detector (PTW, Freiburg) was calibrated across various beam modalities and energies (6 MV photons and 6, 9, 12 MeV electrons) and dose rates (conventional and UHDR electron beams). For the photon beams cross-calibration was performed using Cyberknife calibrated following AAPM’s TG-51. Electron beams were generated using a Mobetron, for which conventional mode was also calibrated using TG-51 while the UHDR absolute dose was determined using alanine dosimeters, with beam fluence correlated between alanine and fD irradiations using an electrostatically shielded beam current transformer. Beam quality dependence was investigated by comparing cross-calibration coefficients for different beam types and energies. Dose rate dependence was evaluated by comparing coefficients for conventional and UHDR electron beams of equivalent energy. Stability was assessed using repeated measurements over two weeks.
Results:
For conventional dose rates, cross-calibration coefficients were 0.159 nC/Gy (6 MeV), 0.160 nC/Gy (9 MeV), and 0.167 nC/Gy (6 MV photons), demonstrating a 4 % difference when comparing measurements in photon and electron beams. For electron beams, the UHDR calibration coefficient was around 5% lower than for conventional dose rates, likely due to saturation of the fD response. However, the fD response exhibited small dose and dose rate dependence (<0.5%) within the range of 80–200 Gy/s. The stability of the response of the fD was within 0.5% over four weeks under UHDR conditions.
Conclusion:
The prototype fD detector demonstrated excellent short-term response stability and negligible dose and dose rate dependence under relevant UHDR conditions. However, a marked beam quality and dose rate dependence was observed between photon and electron beams and between conventional and UHDR electron beams, necessitating further investigation for improved accuracy.