Investigating magnetic field dose effects in small animals: a Monte Carlo study

Abstract

Purpose: In MRI-linac treatments, radiation dose distributions are affected by magnetic fields, especially at high-density/low-density interfaces. Radiobiological consequences of magnetic field dose effects are presently unknown and preclinical studies are desirable. This study investigates the optimal combination of beam energy and magnetic field strength needed for preclinical murine studies. Methods : The Monte Carlo code MCNP6 was used to simulate the effects of a magnetic field when irradiating a mouse lung phantom with a 1.0 cm × 1.0 cm photon beam. Magnetic field dose effects were examined using various beam energies (225 kVp, 662 keV [Cs-137], and 1.25MeV [Co-60]) and magnetic field strengths (0.75 T, 1.5 T, and 3 T). The resulting dose distributions were compared to Monte Carlo results for humans with various field sizes and patient geometries using a 6MV/1.5T MRI-linac. Results: In human simulations, the addition of a 1.5 T magnetic field causes an average dose increase of 49% (range: 36% - 60%) to lung at the soft tissue-lung interface and an average dose decrease of 30% (range: 25% - 36%) at the lung-soft tissue interface. In mouse simulations, no magnetic field dose effects were seen with the 225 kVp beam. The dose increase for the Cs-137 beam was 12%, 33%, and 49% for 0.75 T, 1.5 T, and 3.0 T magnetic fields, respectively while the dose decrease was 7%, 23%, and 33%. For the Co-60 beam the dose increase was 14%, 45%, and 41%, and the dose decrease was 18%, 35%, and 35%. Conclusion : The magnetic field dose effects observed in mouse phantoms using a Co-60 beam with 1.5 T or 3 T fields or a Cs-137 beam with a 3T field fall within the range seen in humans treated with an MRI-linac. These irradiator/magnet combinations are therefore suitable for preclinical studies investigating potential biological effects of delivering radiation therapy in the presence of a magnetic field. --------------------------- Cite this article as: Rubinstein A, Guindani M, Hazle JD, Court LE. Investigating magnetic field dose effects in small animals: a Monte Carlo study. Int J Cancer Ther Oncol 2014; 2(2):020233. DOI: 10.14319/ijcto.0202.33