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An Ionizing Radiation Acoustic Imaging (iRAI) Technique for Real-Time Deep Tissue Dosimetric Measurements for FLASH Radiotherapy

I Oraiqat*, W Zhang, D Litzenberg, K Lam, N Ba Sunbul, J Moran, K Cuneo, P Carson, X Wang, I El Naqa, The University of Michigan, Ann Arbor, MI


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

Room: Track 3

Purpose: In this work, we demonstrate a novel dosimetry method, iRAI, for FLASH-RT, which allows for deep tissue real-time dosimetry, constituting a major breakthrough towards safe and practical clinical implementation of FLASH-RT.

Methods: Two experimental setups were used to study the feasibility of iRAI for FLASH-RT (using 6 MeV electrons from a modified Varian Clinac). First, experiments were conducted using a single element focused transducer to take a series of point measurements in a gelatin phantom, which was compared with independent dose measurement using GAFchromic films. Second, a phased array transducer was used to take 2D iRAI signal amplitude images as well as capture ultrasound B-mode images to map dose deposition with respect to the surrounding anatomy in an ex vivo rabbit liver with a single Linac pulse precision.

Results: Using the single element transducer, iRAI measurements show a linear relationship between the iRAI amplitude and dose per pulse (r² = 0.9998) and high accuracy (1%) when compared with GAFchromic film. Additionally, a depth dose curve was generated that agrees with film after using a correction factor that takes into account changes in measurement conditions with respect to calibration conditions (RMSE of 0.0243). Using the phased array, a 2D iRAI map was generated using a single linac pulse and is registered with B-mode ultrasound to provide beam targeting with respect to soft-tissue anatomy.

Conclusion: This work demonstrates the potential of using iRAI for real-time deep tissue dosimetry for FLASH-RT. We demonstrated that iRAI signals are linear with dose and can map radiation dose with soft tissue anatomy. With its ability to measure dose for individual linac pulses at any location within soft tissue while knowing where that dose is being delivered anatomically in real time, iRAI can be a powerful tool to enable safe and practical clinical translation of FLASH-RT.


FLASH Radiotherapy, Radiation Acoustics, In-vivo Dosimetry


Not Applicable / None Entered.

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