J Ryser*, A Husain, M Huang, K Shoniyozov, L Dong, Y Fan, E Diffenderfer, J Zou, University of Pennsylvania, Philadelphia, PA

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  J Ryser

(Saturday, 3/26/2022) 10:30 AM - 12:30 PM [Central Time (GMT-5)]

Room: Celestin D-E

Purpose: For small animal experiments under conventional and FLASH dose-rates with small-field proton beams, we developed and implemented a method for dose calibration and monitoring using a Faraday cup, a parallel-plate ion chamber and radiochromic films.

Methods: First, we determined a relationship between dose and optical density (OD) of EBT_XD Gafchromic™ film using scanned 30x30 cm² proton pencil beams delivered at clinical dose-rates. The dose was measured with an Advanced Markus chamber. Then, the double-scattered pencil beams at ultra-high dose-rates (130±7 Gy/s) were delivered to the film through an 8 mm diameter brass collimator, and the proton fluence charge was collected by a Faraday cup placed downstream from the film. The average of the film OD profile was related to the Faraday cup charge. Finally, we obtained a conversion from Faraday cup charge to average dose of the small-field proton beam.

Results: The relationship between the small-field average profile dose and Faraday cup charge was established for 10 and 15 Gy. Repeating the calibration procedure at conventional dose-rates (0.77±0.04 Gy/s) revealed that the film OD is independent of dose-rate. Before each small animal treatment, the durations of the proton beams at FLASH and conventional dose-rates were set against the Faraday cup readings. The doses to the small animals were monitored with the Faraday cup and found to be 10±0.23 and 15±0.29 Gy for 60 mice irradiated.

Conclusion: We established a dose calibration and monitoring method for small animal proton FLASH experiments with small-field irradiation. Because of the convenient conversion from Faraday cup charge to dose, this method has been used for experiments in an ongoing preclinical FLASH study for mice with medulloblastoma tumors.

Keywords

Protons, Radiation Dosimetry, Small Fields

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – experimental dosimetry

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