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BEST IN PHYSICS (THERAPY): Ionized Radiation Acoustic Imaging (iRAI) for In-Vivo FLASH Dosimetry

N Ba Sunbul*, I Oraiqat, W Zhang, S Clarke, M Matuszak, S Pozzi, I El Naqa, University of Michigan, Ann Arbor, MI


(Monday, 7/13/2020) 3:30 PM - 5:30 PM [Eastern Time (GMT-4)]

Room: Track 3

The aim of this work is to demonstrate through simulation studies the feasibility of Ionizing Radiation Acoustic Imaging (iRAI) as a promising relative in-vivo dosimetric tool for ultra-high dose rate radiotherapy (FLASH-RT).


The detection of induced acoustic waves following a single FLASH-RT pulse of a modified 6 MeV 21EX Varian Clinac in a gelatin phantom was simulated using an ideal ultrasound transducer. The full 3D dose distributions in the phantom for the 1x1 cm² electron field were simulated using EGSnrc (BEAMnrc\DOSXYZnrc) Monte Carlo codes and converted into an initial pressure source distribution using the medium dependent dose-pressure relation. The MATLAB based toolbox k-Wave was then used to model propagation of acoustic waves through the phantom and for reconstructing the resulting image. The simulated depth pressure (dose) curves and beam profiles were compared with film measurements from the modified Linac setup.


The Monte Carlo dose simulation results were in good agreement with the film measurement specifically at the central 80% dose region with ~2% error for the central profile region and <3.5% for PDD.
IRAI was capable of identifying the central beam edges within ~3.85% of the film measurement. The pressure signal change was in agreement with the dose changes demonstrating iRAI capability for predicting the beam position based on the pressure signal measured in real time. IRAI was verified through 2D simulations to be capable of measuring changes in the Linac operation parameters on a dose per pulse basis as expected theoretically from the pressure-dose proportionality.

A simulation work flow was developed for testing the feasibility of iRAI as a promising relative dosimetry tool for FLASH-RT. IRAI has the potential to be a useful dosimeter for at depth beam localization and potentially for in-vivo dosimetry in FLASH-RT, which is currently unattainable with common measurements.


FLASH Radiotherapy, Radiation Acoustics, Ultrasound


Not Applicable / None Entered.

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