Technical Note: A Monte Carlo study of magnetic-field-induced radiation dose effects in mice.
OBJECTIVE
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 [Cs-137], 2 MV, and 1.25 MeV [Co-60]) 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.
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030 and The University of Texas Graduate School of Biomedical Sciences, Houston, Texas 77030.
Ashley E
AE
Rubinstein
Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
Zhongxing
Z
Liao
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
Adam D
AD
Melancon
Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
Michele
M
Guindani
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
David S
DS
Followill
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
Ramesh C
RC
Tailor
Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
John D
JD
Hazle
Departments of Radiation Physics and Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030.
Laurence E
LE
Court
D000818:Animals; D006801:Humans; D008168:Lung / Q000528:radiation effects; D060526:Magnetic Fields; D051379:Mice; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage