Monte Carlo assessment of beam deflection and depth dose equivalent variation of a carbon-ion beam in a perpendicular magnetic field

Abstract

Purpose: To evaluate beam deflection and dose equivalent perturbation of carbon-ion (C-ion) versus depth in a perpendicular magnetic field with the motivation of application to potential future development of MRI-guided carbon therapy. Methods: A therapeutic beamline, a rectangular water phantom (homogeneous) and a multi-layer tissue phantom were simulated by applying the FLUKA Monte Carlo simulation code. The C-ion beam deflection variation against depth inside the water phantom at 100, 220 and 310 MeV/nucleon (MeV/n) was calculated in the presence of 0.5, 1.5 and 3 T magnetic fields. The 220 MeV/n primary ion depth dose equivalent variations induced by a 1.5 T field were calculated inside the homogeneous and multi-layer phantoms. Results: The calculated deflections were ranging from 0 to 10.5 mm. The Bragg depth did not change by applying a 1.5 T field to both phantoms under study at 220 MeV/n energy. The dose equivalent in the Bragg depth inside the homogeneous and multi-layer tissue phantoms was found to be reduced by 5.1% and 2.95%, respectively. A dose equivalent reduction of 5.77% in the Bragg depth was obtained when an air layer of 1.8 cm thick was added to the multi-layer phantom. Conclusion: Dose equivalent perturbation and beam deflection become important at energies above 100 MeV/n, in both phantoms affected by a 1.5 T magnetic field. © 2019 Associazione Italiana di Fisica Medica