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Deliver Proton FLASH Beams with a Saturated Monitor Chamber for Pre-Clinical Studies

H Lin1*, Y Yang2, G Yu3, M Kang4, S Wei5, S Huang6, Q Chen7, h Zhai8, C Chen9, M Folkerts10, C Shi11, (1) New York Proton Center, New York, NY, (2) New York Proton Center, New York, NY, (3) New York Proton Center, New York, NY, (4) New York Proton Center, New York, NY, (5) New York Proton Center, New York, NY, (6) New York Proton Center, New York, NY, (7) New York Proton Center, New York, NY, (8) New York Proton Center, New York, NY, (9) New York Proton Center, New York, NY, (10) Varian Medical Systems, Palo Alto, CA, (11) New York Proton Center, New York, NY

Presentations

TU-D1030-IePD-F3-3 (Tuesday, 7/12/2022) 10:30 AM - 11:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: This study presents workarounds to overcome challenges when operating a ProBeam system in FLASH research-only mode for pre-clinical experiments. The challenges arise due to ultra-high beam currents (>20nA) saturating the machine’s monitoring chamber (MC).

Methods: Our FLASH experience is based on performance in one horizontal-beamline research room and one gantry room. The top three issues impacting performance and safety caused by the saturated MC are discussed. 1. under-reporting of delivered monitor units (MUs); 2. Machine output variations due to beam current fluctuation; 3. Radiation shielding and workload limits. Workaround and institutional recommendations for dose rate limits are proposed. We present our experience and recommendations for each major concern as a reference for other ProBeam centers conducting FLASH pre-clinical research and facing the same challenges.

Results: The system delivered more doses than requested due to MC saturation. This dose deviation depends on beam current and MU/spot. The relationship between planned and delivered doses were established to determine an MU scaling factor. The delivery is repeated 2-3 times, and the measured dose is averaged to fine-tune MU scaling factor, minimizing the impact of output variations to achieve an accurate dose delivery. The highest radiation survey reading in the clinical area was identified at the gantry 90 degrees in the clinical gantry room and along the beam direction in the imaging suite of the adjacent treatment room. Hourly and daily limits in a unit of nAseconds are recommended based on conservative evaluation of the radiation survey and occupancy factors of hot locations.

Conclusion: Understanding the ProBeam Figursystem behavior and safety concerns is critical when operating in FLASH research-only mode with a saturated MC. Institutional protocols, workflows, and safety guidelines should be developed to address the critical issues before using the system for research and pre-clinical experiments.

Keywords

Protons, Monitor Chambers, Radiation Therapy

Taxonomy

Not Applicable / None Entered.

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