Author: Seohyeon An, Yoonsun Chung, Seonghoon Jeong, Seongmoon Jung, Chae-Eon Kim, In Jung Kim, Sung Hun Kim, Se Byeong Lee, Sang-il Pak, Jong In Park 👨🔬
Affiliation: POHANG ACCELERATOR LABORATORY, Hanyang University, Korea Research Institute of Standards and Science (KRISS), Ilsan Paik Hospital, National Cancer Center, National Cancer Center Korea, Korea Research Institute of Standards and Science 🌍
Purpose: To evaluate the performance of three ion chambers—Advanced Markus (AMC), PinPoint, and Roos—under FLASH proton beam conditions and assess the response of the nozzle monitor chamber for their suitability in FLASH dosimetry.
Methods: A 228 MeV pristine Bragg Peak FLASH proton beam with a dose rate of 66 Gy/s was generated using a PROTEUS 235 system (IBA, Belgium) at the National Cancer Center Korea. A custom time control system based on Raspberry Pi 4 Model B enabled beam control with 1 ms resolution. Ion chamber performance was assessed at a 2 cm depth in a water-equivalent phantom following the revised TRS-398 protocol. To validate the accuracy of the ion chamber measurements, alanine dosimetry was used as a reference dosimetry method. The nozzle monitor chamber was evaluated by varying irradiation time and cyclotron current to analyze response.
Results: The nozzle monitor chamber exhibited saturation with increasing cyclotron current, while the responses of the ion chambers remained linear. Differences in chamber response due to sensitive volume were corrected, confirming the feasibility of using PinPoint and Roos chambers alongside AMC in FLASH proton environments.
Conclusion: This study confirmed the measurement capabilities of each ionization chamber under FLASH proton beam conditions. Through corrections based on the Advanced Markus Chamber (AMC), which is commonly used as a secondary standard, the PinPoint and Roos chambers were also found to be feasible for use in FLASH proton dosimetry.