The Ionizing Radiation Laboratory participates in the activities in WP1 and WP2 and as WP Leader of WP2. All planned activities were carried out and completed.
The METAS accelerator for FLASH-RT was optimized on the basis of the beam parameters for FLASH radiotherapy (RT) compiled by the CHUV. The beam profile was characterized and compared with associated Monte Carlo simulations calculated at GUM. For these relative measurements, measurements with demonstrably dose rate-independent EBT3 films were introduced at METAS.
When parameterizing the radiochemical yield factor of the Fricke dosimeter, the dose rate was varied between (0.3 - 900) mGy/pulse. The dose of the Fricke dosimeter was compared with measurements of two different ionization chamber types (Roos and Adv. Markus chamber) and additionally with alanine dosimeters of the PTB and EBT3 films. In addition, Fricke dosimeters with (0.1 - 10) Gy/pulse were irradiated at the CHUV with their UHD accelerator. The Fricke dose was compared with that of EBT3 film.
However, the measured values fit well into the series of measurements and indicate that the Fricke dosimeter is dose rate-dependent from >1 Gy/pulse.
The information obtained from this was then used to establish the Fricke primary standard (total absorption). For this purpose, the current measurement was additionally calibrated traceable to a calibrated PTB current source in spring 2022. The primary realization of the absorbed dose to water for UHD electron radiation was compared with the calorimetric primary realization of PTB using alanine irradiations of the NRC (Canada) in summer 2022. The analysis of NRC shows that the two standards agree within the combined measurement uncertainty R METAS/PTB = 1.002 +/- 0.012 (k=1).
In addition, a specific Adv. Markus chamber was used by both METAS and PTB for comparison measurements. A close examination of these results has shown that for ionization chambers - used with FLASH-RT dose rates - not only an individual, serial number-specific determination of the saturation correction is essential, but also that the influence of the air pressure on the saturation correction must be taken into account to a higher degree than usual.
As WP2 leader, METAS was also involved in the project organization and project reporting. In this context, METAS co-authored interim reports, chaired the corresponding sessions at project meetings and monitored and presented the progress of the entire WP.