Commissioning a Fixed Field FLASH Pencil Beam Scanning Proton Therapy System in Support of the First In-Human Clinical Trial
A Mascia1,2*, Y Zhang1,2, E Lee1,2, Z Xiao1,2, J Speth1,2, M Sertorio2, E Abel3, M Folkerts3, A Lourenco4, N Lee5, A Subiel5, F Romano5, R Thomas5, R Amos4, J Breneman6, (1) University of Cincinnati Medical Center, Cincinnati, OH (2) Cincinnati Children's Hospital Medical Center, Cincinnati, OH (3) Varian Medical Systems, Palo Alto, CA (4) University College London, London, GB (5) National Physical Laboratory, Teddington, GB (6) University of Cincinnati, Cincinnati, OH
Presentations
SU-IePD-TRACK 5-4 (Sunday, 7/25/2021) 5:30 PM - 6:00 PM [Eastern Time (GMT-4)]
Purpose: Ultra-high dose rate radiotherapy, or FLASH radiotherapy (FRT), delivers therapeutic doses at dose rates exceeding 40Gy/s. With small modifications, some modern proton therapy systems are capable of treating deep-seated tumors with FRT. Pre-clinical and translational data shows potential for normal tissue sparing at ultra-high dose rates with no reduction in tumor control. FAST-01, the first in-human proton therapy FLASH clinical trial, began accruing patients in late 2020.
Methods: For FAST-01, the pencil beam scanning proton therapy system delivers pre-defined FLASH treatment plans using a 250MeV transmission beam at a minimum of 40Gy/s. Commissioning and characterization of the delivery system was performed using, primarily, ion chamber and film. A treatment planning beam model was validated and end-to-end tests performed. The shielding was evaluated for the FRT trial doses and dose rates. A quality assurance program was adapted to include FLASH deliveries.
Results: The parallel plate ion chamber was validated against a graphite calorimeter, with agreement within 1.0%. The radiochromic film dose-response curve was calibrated in the FLASH fields, cross-calibrated to the parallel plate ion chamber. A treatment planning beam model was created and validated for transmission FLASH fields. The machine trend analysis shows absolute dose variation within 1% and dose rate variation within 5% and always above 40Gy/s threshold. End-to-end tests and shielding evaluations all passed. Patient QA results meet a 90% passing rate at gamma criteria of 3%/3mm. Initial FLASH clinical treatments are performed with little modification to standard clinical workflow. In vivo dosimetry and log file analysis further confirms the accuracy and constancy of the FRT treatment delivery.
Conclusion: While following a standard commissioning methodology while also adhering to a quality assurance program that includes special consideration with respect to dose rate, the proton therapy system is capable of safe and efficient FLASH radiotherapy.
Funding Support, Disclosures, and Conflict of Interest: Funding/support from Varian Medical Systems
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