Author: Abdullah A. Alshreef, Grant A. McAuley, Jerry D Slater 👨🔬
Affiliation: Loma Linda University Medical Center, Loma Linda University 🌍
Purpose: In this project we investigate the use of a single permanent magnet quadrupole to create pass-through proton minibeams suitable for potential clinical use and preclinical radiobiology experiments
Methods: Monte Carlo simulations were performed using TOPAZ 3.9 with 250 MeV protons using Gaussian symmetric beam models (σ = 5 mm; σ’ = 2 mrad) focused by a single quadrupole modelled as a Halbach cylinder. Symmetric and planar beamlets were produced by modelling an axial spinning or stationary magnet, respectively. Dose distributions of single beamlets were scored in a water phantom, and minibeam composite dose distributions were created by laterally shifting beamlet distributions in the phantom. A pilot experiment analogous to the MC simulations was performed simulating the rotation of the magnet by rotating EBT3 film.
Results: Simulations produced symmetric beamlets with minimum FWHM = 3.4 mm at a 78 mm depth. Dose at this depth was ~ 7 times larger than at 150 mm. A preliminary pilot experiment analogous to the MC simulations consisting of only a 9% rotation showed a FWHM = 4.6 mm at 78 mm WED.
Conclusion: A single high lens power quadrupole permanent magnet can potentially be used to create symmetric and planar proton pass-through minibeams using standard clinical energies suitable for potential clinical use as well as radiobiology experiments.