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Session: Therapy: FLASH Techniques [Return to Session]

Development and Validation of a FLASH Pencil Beam Scanning Beam Model for Treatment Planning and Verification in First In-Human Trial

Y Zhang1,2*, E Lee1,2, Z Xiao1,2, J Speth1,2, M Folkerts4, E Abel4, J Breneman3, A Mascia1,2, (1) University of Cincinnati Medical Center, Cincinnati, OH (2) Cincinnati Children's Hospital Medical Center, Cincinnati, OH(3) University of Cincinnati, Cincinnati, OH (4) Varian Medical Systems, Palo Alto, CA


SU-IePD-TRACK 5-5 (Sunday, 7/25/2021) 5:30 PM - 6:00 PM [Eastern Time (GMT-4)]

Purpose: State-of-art clinical proton accelerators can readily deliver scanning proton beam at ultra-high dose rate. While conventional PBS beam models were validated for dose accuracy in an SOBP, the purpose of this work is to develop and validate a dose calculation model in support of treatment planning and verification under single-layer transmission mode.

Methods: FAST-01, the first in-human clinical trial for proton FLASH, adopted a library of pre-defined 250MeV rectangular plans to cover a variety of field size, ranging from 7.5x7.5cm to 7.5x20cm. The required beam data, including depth dose, in-air spot and absolute dose, are acquired, processed and calculated to create a beam model in Varian Eclipse. Prior to validations, reference dosimetry was established using a calorimeter, and absolute dose was cross-validated using various detectors at both conventional and FLASH dose rate. The beam model was validated for the pre-defined library of plans delivered in the gantry in FLASH mode. Ion chamber measurements at different locations using a parallel plate chamber were compared to the calculation. Radiochromic film was also deployed to validate 2D dose distribution using gamma analysis in mock and real patients.

Results: The measurement results were compared against dose calculations from FLASH beam model in Eclipse. For the plan library, the overall dose deviation was 0.2%±1.3% at 1cm and 5cm depths. So far, FAST-01 has accured four patients. For patient QA, the absolute doses were measured at 5cm using PTW Advanced Markus chamber. Cross-calibrated Gafchromic EBT3 film was used to acquire 2D dose distribution for gamma analysis. For these patients, the average dose difference was 1.8%±0.3%, and 2D gamma index all passed 90% at 3mm/3%.

Conclusion: The validation results have demonstrated that the beam model is an accurate and indispensable tool for transmission flash planning and dose verification in support of trial.

Funding Support, Disclosures, and Conflict of Interest: The research is supported by Varian Medical System



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