Proton Radiography with FLASH Dose Rates
A Stanforth1*, S Charyyev1, J Arrue2, M Duce2, A Erickson2, A Dhabaan1, (1) Emory Univeristy, Atlanta, GA,(2) Gerogia Institute of Technology, Atlanta, Atlanta, Ga
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PO-GePV-M-92 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: FLASH has shown great potential to reduce normal tissue toxicity. Proton FLASH most often uses the highest energy available with a shoot-through plan. The protons exiting the patient can be used to image and reveal valuable information for the validation of the tumor position and delivered dose. We investigate the use of a detector panel for use for FLASH proton radiography, specifically looking at the effect MU per spot and nozzle current have on image quality and contrast and motion artifacts.
Methods: A radiation hardened amorphous silicon flat-panel detector was used in frame mode with an anthropomorphic and a motion phantoms. Each raw image is obtained by summing all frames and then post-processed using in-house analysis tools. We investigated the effects of MU per spot and nozzle current on image quality, as well as tumor size and extent/speed of target motion. Square fields with even spot spacing were used. MU per spot was varied between 3 and 10. Nozzle current was varied between 1 and 20 nA and phantom motion between 2 seconds/cycle and 10 seconds/cycle. Images were evaluated qualitatively.
Results: Anatomic features were easily distinguished at a low number of MU/spot. As MU/spot increases, contrast decreases, and imaging artifacts increase. The time resolution of the panel can detect tumor motion. At an intermediate nozzle current, no motion artifacts are visible in the image.
Conclusion: This study shows a proof-of-concept for using proton shoot-through FLASH to image moving targets. This study also shows that image contrast and visibility of anatomic features are dependent on MU/spot with low MU/spot is favorable. This leads to minimum dose delivery to patient with proton imaging.
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