Monte Carlo Investigation of Planar Electron Mimbeams Created by a Single Halbach Cylinder
GA McAuley*, JD Slater, Department of Radiation Medicine, Loma Linda University, Loma Linda, CA
Presentations
PO-GePV-T-75 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To investigate the potential to create planar electron minibeams using a single quadrupole Halbach cylinder
Methods: Monte Carlo simulations of 12 MeV electrons focused by a single quadrupole Halbach cylinder of length 30 mm, 25 mm bore diameter and field gradients of 60 T/m were performed in a model of a clinical linac using the TOPAS Geant4-based software application. The simulated magnets mimic Halbach cylinders that can be manufactured commercially as assemblies of radiation-hard Sm2Co17. Resultant dose distributions of single beamlets were scored in a water phantom comprised of 0.2 x 0.2 x 0.5 mm voxels. Composite dose distributions were created by laterally shifting copies of the single beamlet distribution to either side of the central beamlet with a center-to-center beamlet spacing chosen to achieve a quasi-homogeneous dose at target depth. Simulations with other energies and magnet configurations are ongoing.
Results: The single magnet produced planar beamlets with very narrow and elongated cross sections. The associated dose distribution displayed a high degree of spatial fractionation at entrance that blended into a quasi-homogenous distribution at a 15 mm WED target depth. At phantom entrance, PVDR was 140 and the horizontal FWHM was 0.9 mm for the composite beams (consisting of 5 beamlets).
Conclusion: Electron minibeam dose distributions with high PVDR and sub-millimeter FWHM beamlets can be produced by a single quadrupole Halbach cylinder with commercially available specifications. These permanent magnet cylinders have low external magnetic fields and do not require power or cooling. Coupled with precise 1D motion control, the proposed method could be used in existing linacs for inexpensive preclinical minibeam radiobiology investigations (potentially including FLASH implementations).
Keywords
Electron Therapy, Monte Carlo, Radiobiology
Taxonomy
TH- External Beam- Electrons: Development (new technology and techniques)
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