Author: Fu-Xiong Chang, Arpit M. Chhabra, J Isabelle Choi, Chanda Guha, Nancy Y Lee, Chih-Hsun Lin, Haibo Lin, Hang Qi, Mahbubur Rahman, Charles B. Simone, Pingfang Tsai, Shouyi Wei, Irini Yacoub, Yunjie Yang, Ajay Zheng, Jun Zhou 👨🔬
Affiliation: New York Proton Center, Montefiore Medical Center and Albert Einstein College of Medicine, Liverage Biomedical Inc., Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, Memorial Sloan Kettering Cancer Center, Department of Radiation Oncology and Winship Cancer Institute, Emory University, Institute of Physics, Academia Sinica 🌍
Purpose: FLASH therapy presents an opportunity to alter the radiotherapy paradigm and significantly enhancing normal organ protection while maintaining the effectiveness of tumor control. The temporal resolution and saturation of existing detectors, however, are persisting challenges for FLASH dosimetry. We report a novel 2D discrete ionization chamber array (DICA) designed for the FLASH and conventional dosimetry with high spatiotemporal resolution.
Methods: The DICA contains 2025 mini parallel plate ion chambers (0.02 cc sensitive volume) with 3mm center-to-center distance and can measure a 13.5 cm x 13.5 cm radiation field. The DICA was tested for a 5 cm x 5 cm proton beam with 5 mm spot spacing on the Varian ProBeam system with a maximum 250-MeV proton beam with nozzle currents of 2-215nA. The dose-response of DICA was cross-calibrated with the PTW Advanced Markus chamber. The spatial, temporal and dosimetric performances of the DICA were characterized and compared to Monte-Carlo simulation.
Results: The sampling rate of 1kHz (1ms) was sufficient to resolve each single spot delivery for a wide dose rate range (nozzle beam currents: 2-215nA). A high dose linearity of R2 > 0.99 was achieved for a beam current of 2/100/215nA and indicated a high dynamic response range for absolute dose measurement in both conventional and FLASH conditions. With a given signal gain setting, the signal rate linearly increased with beam current up to ~100nA and exhibited a nonlinear trend beyond 100nA. Calibration for each FLASH beam current and signal gain combination or the implementation of a dynamic signal gain mechanism is needed to ensure dose linearity. 2D dose and dose rate distributions at 215nA were measured and compared to Monte-Carlo simulation.
Conclusion: The newly designed DICA demonstrated excellent spatial, temporal and dosimetric performance, critical to future FLASH radiotherapy applications