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Session: FLASH – Platforms and Instrumentation [Return to Session]

A High Spatiotemporal Resolution 2D Strip Ionization Chamber Array for Proton Pencil Beam Scanning FLASH Radiotherapy

Y Yang1*, C Shi1, C Chen1, P Tsai1, S Huang1, M Kang1, C Lin2, F Chang3, A Chhabra1, I Choi1, W Tome4, C Simone1, H Lin1, (1) New York Proton Center, New York, NY, (2) Academia Sinica, Taiwan, (3) Liverage Biomedical Inc., Taiwan, (4) Montefiore Medical Center, Bronx, NY


WE-D-BRA-1 (Wednesday, 7/13/2022) 10:15 AM - 11:15 AM [Eastern Time (GMT-4)]

Ballroom A

Purpose: Experimental measurements and validation of 2D dose rate distributions in proton pencil beam scanning (PBS) FLASH radiation therapy (RT) are currently lacking. In this work, we characterize a newly designed 2D strip-segmented ionization chamber array (SICA) with high spatial and temporal resolution and demonstrate its applications in a modern proton PBS delivery system for FLASH-RT.

Methods: A dedicated research beamline of the Varian ProBeam system was employed to deliver a 250 MeV proton PBS beam with nozzle currents up to 215 nA. The spatial, temporal, and dosimetric performance of the SICA was characterized and compared with measurements using a parallel-plate ion chamber (PTW Advanced Markus chamber), Gafchromic films (EBT-XD), and a Faraday Cup. A novel reconstruction approach for 2D strip ionization chamber was proposed and enabled the first experimental measurements of the 2D dose rate distributions under a proton PBS FLASH-RT delivery using the SICA.

Results: The SICA demonstrated a position accuracy of 0.12 ± 0.02 mm at a 20 kHz sampling rate (50 μs per event) and a linearity of R² > 0.99 for both dose and dose rate with respect to nozzle beam currents ranging from about 1 nA to 215 nA. The 2D dose comparison to the film measurement resulted in a gamma passing rate of 99.8% (2 mm/2%). The measured proton PBS 2D FLASH dose rate distribution was compared to simulation results and showed a gamma passing rate of 97.3% (2 mm/2%).

Conclusion: The newly designed SICA demonstrated excellent spatial, temporal, and dosimetric performance and is well suited for commissioning, quality assurance (QA), and a wide range of clinical applications in proton PBS FLASH radiotherapy.


Protons, Quality Assurance, Ionization Chamber


TH- External Beam- Particle/high LET therapy: Proton therapy – quality assurance

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