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Published on: May 9, 2014
Thick Gas Electron Multiplier-based Air Ionization Chamber for Online Dose Monitoring in Conventional and FLASH
Tianli Qiu1, Feng Yang2, Yi Peng2
1Department of Radiation Oncology, Precision Radiation in Oncology Key Laboratory of Sichuan Province, Sichuan Cancer Hospital and Institute, University of Electronic Science and Technology of China, Chengdu, China; School of Medicine, University of Electronic Science and Technology of China, Chengdu, China.
Purpose:
The aim of this work was to develop an online dose monitoring device that can be applied to both conventional radiation therapy (RT) and ultrahigh dose rate RT.
Methods And Materials:
Thick Gas Electron Multiplier (THGEM) technology, with its uniform microstructure characteristics, emerges as an ideal solution to these challenges. This study introduces an innovative approach by covering both THGEM electrodes with Mylar conductive films, creating independent microionization chambers in each microhole that effectively reduce charge density issues in high dose rate environments.
Results:
Experimental results demonstrate that the developed THGEM-based air ionization chamber (THGEM-ADIC) exhibits nearly identical linear response to the standard PTW Farmer 30013 ionization chamber over a dose range of 1-100 Gy in conventional RT settings, with dose deviations within ±3% and a stable operational plateau of approximately 400 V. Accuracy at clinical single-field doses typical of intensity modulated RT or fractionated treatments remains to be investigated. More importantly, benefiting from its unique microstructure design, THGEM-ADIC has rapid signal response, enabling direct measurement of FLASH radiation therapy accelerator macro-pulse structures. In ultrahigh dose rate (UHDR) working environments, the detector maintains an operational plateau of about 200 V and demonstrates a dose response with linearity exceeding 99% compared with EBT3 film dosimetry measurements, even at extreme dose rates up to 250 Gy/s. However, a dose rate dependence was observed between 50 and 250 Gy/s under UHDR conditions, which should be taken into account for accurate dosimetry at UHDRs.
Conclusions:
Collectively, these results indicate that THGEM-ADIC, with its microstructure design and rapid response capabilities, not only provides measurement accuracy consistent with traditional ionization chambers in conventional RT but also enables precise dose monitoring under UHDR FLASH radiation therapy conditions, offering an important dosimetric tool for the clinical translation of FLASH-RT technology.
