Characterizing the Stray Radiation Fields at a FLASH Therapy Facility Using Gas-filled Ionization Chamber with an ASIC Front-end

Ultra-high dose rate radiation therapy is gaining momentum in the treatment of cancer. Many recent studies have shown promising results with great potential. The instrumentation required for commercial, reliable therapy facilities is continuously evolving. Such facilities however face the challenge of developing radiation monitors with a wide dynamic range to ensure the safe operation and protection of the personnel. There is a shortage of reported work in this domain. The main challenge for radiation monitoring in such environments comes from the complex nature of the generated pulses. The dose delivered could be of the order of 5 Gy per pulse with a very short pulse width in the range of microseconds and a period of less than a second. The pulses could also be accompanied by pre and post-pulses which could be orders of magnitude less than the main pulse. The accurate measurement of the generated doses at different locations of a facility is paramount from a radiation protection perspective. This contribution summarizes the characterization performed recently at a FLASH radiation facility where gas-filled ionization chambers were used as radiation sensors. The specifically designed front-end electronics for these chambers is also detailed. The front-end utilizes a custom-designed ASIC which enables accurate measurements of the charges generated by the ionization chamber. It was seen that using the ionization chamber-based radiation monitor, the dose rates at different points in a treatment room could be measured and the time structure of the pre and post-pulses be recorded. The first results obtained on the linearity of the device and the saturation behaviour were encouraging. We will continue to investigate ionization chambers for pulsed radiation monitoring in FLASH therapy applications in the future with a focus on the dose calibration and the accuracy of the measurements.