Technical Note: A Monte Carlo study of magnetic‐field‐induced radiation dose effects in mice

Abstract

Purpose: Magnetic fields are known to alter radiation dose deposition. Before patients receive treatment using an MRI-linear accelerator (MRI-Linac), preclinical studies are needed to understand the biological consequences of magnetic-field-induced dose effects. In the present study, the authors sought to identify a beam energy and magnetic field strength combination suitable for preclinical murine experiments. Methods: Magnetic field dose effects were simulated in a mouse lung phantom using various beam energies (225 kVp, 350 kVp, 662 keV , 2 MV, and 1.25 MeV ) and magnetic field strengths (0.75, 1.5, and 3 T). The resulting dose distributions were compared with those in a simulated human lung phantom irradiated with a 6 or 8 MV beam and orthogonal 1.5 T magnetic field. Results: In the human lung phantom, the authors observed a dose increase of 45% and 54% at the soft-tissue-to-lung interface and a dose decrease of 41% and 48% at the lung-to-soft-tissue interface for the 6 and 8 MV beams, respectively. In the mouse simulations, the magnetic fields had no measurable effect on the 225 or 350 kVp dose distribution. The dose increases with the Cs-137 beam for the 0.75, 1.5, and 3 T magnetic fields were 9%, 29%, and 42%, respectively. The dose decreases were 9%, 21%, and 37%. For the 2 MV beam, the dose increases were 16%, 33%, and 31% and the dose decreases were 9%, 19%, and 30%. For the Co-60 beam, the dose increases were 19%, 54%, and 44%, and the dose decreases were 19%, 42%, and 40%. Conclusions: The magnetic field dose effects in the mouse phantom using a Cs-137, 3 T combination or a Co-60, 1.5 or 3 T combination most closely resemble those in simulated human treatments with a 6 MV, 1.5 T MRI-Linac. The effects with a Co-60, 1.5 T combination most closely resemble those in simulated human treatments with an 8 MV, 1.5 T MRI-Linac. C 2015 American Association of Physicists in Medicine. [http://dx

Technical Note: Dose effects of 1.5 T transverse magnetic field on tissue interfaces in MRI-guided radiotherapy

“…On the other hand, the increase of D max in the HN case is only 1.6% (1.24 Gy). In a recent paper that used a Monte-Carlo analysis of the dose effect of magnetic field on human lung and mouse lung phantoms, Ashley et al 16 observed a dose increase of 45% at the tissue-to-lung interface and a dose decrease of 41% at the lung-to-tissue for a single beam orientation. However, these large dose changes are not observed in the cases we studied where multiple beam orientations are used.…”

Measurement validation of treatment planning for a MR‐Linac

“…The dosimetric effect of a transverse magnetic field (TMF) in phantom and patients has been studied extensively . Compared to conventional external beam RT without magnetic field, the magnetic field can generally lead to an altered buildup depth, and a larger, slightly shifted (asymmetric) penumbra arising from tilting of the dose kernel .…”

Effect of Low Magnetic Field on Dose Distribution in the Partial-Breast Irradiation

“…The consequences of these changes on dose distribution for radiotherapy treatment with a magnetic field have been studied by many groups using analytical, simulation and/or experimental techniques. [13][14][15] Largely, the focus has been on changes to the spatial distribution of dose resulting from the magnetic field influence on charged particle transport. The high magnetic field strength can have significant perturbations on dose distributions, such as changes to the percentage depth dose, tissue interface effects and lateral shifts in dose distributions in the photon beam radiotherapy.…”