A simulation study of ionizing radiation acoustic imaging (iRAI) as a real‐time dosimetric technique for ultra‐high dose rate radiotherapy (UHDR‐RT)

• Published in: Medical physics (Lancaster) 2021-10, Vol.48 (10), p.6137-6151
• Main Authors: Ba Sunbul, Noora H., Zhang, Wei, Oraiqat, Ibrahim, Litzenberg, Dale W., Lam, Kwok L., Cuneo, Kyle, Moran, Jean M., Carson, Paul L., Wang, Xueding, Clarke, Shaun D., Matuszak, Martha M., Pozzi, Sara A., El Naqa, Issam
• Format: Article
• Language: English
• Subjects: Acoustics; Animals; in vivo dosimetry; Monte Carlo; Monte Carlo Method; Particle Accelerators; Phantoms, Imaging; radiation acoustics; Radiation, Ionizing; Radiometry; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Swine; UHDR (Flash) radiotherapy
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1002/mp.15188

Purpose Electron‐based ultra‐high dose rate radiation therapy (UHDR‐RT), also known as Flash‐RT, has shown the ability to improve the therapeutic index in comparison to conventional radiotherapy (CONV‐RT) through increased sparing of normal tissue. However, the extremely high dose rates in UHDR‐RT have raised the need for accurate real‐time dosimetry tools. This work aims to demonstrate the potential of the emerging technology of Ionized Radiation Acoustic Imaging (iRAI) through simulation studies and investigate its characteristics as a promising relative in vivo dosimetric tool for UHDR‐RT. Methods The detection of induced acoustic waves following a single UHDR pulse of a modified 6 MeV 21EX Varian Clinac in a uniform porcine gelatin phantom that is brain‐tissue equivalent was simulated for an ideal ultrasound transducer. The full 3D dose distributions in the phantom for a 1 × 1 cm2 field were simulated using EGSnrc (BEAMnrc∖DOSXYZnrc) Monte Carlo (MC) codes. The relative dosimetry simulations were verified with dose experimental measurements using Gafchromic films. The spatial dose distribution was converted into an initial pressure source spatial distribution using the medium‐dependent dose–pressure relation. The MATLAB‐based toolbox k‐Wave was then used to model the propagation of acoustic waves through the phantom and perform time‐reversal (TR)‐based imaging reconstruction. The effect of the various linear accelerator (linac) operating parameters, including linac pulse duration and pulse repetition rate (frequency), were investigated as well. Results The MC dose simulation results agreed with the film measurement results, specifically at the central beam region up to 80% dose within approximately 5% relative error for the central profile region and a local relative error of