Lee HJ, et al. - An investigation was performed of the effects of strong magnetic fields on 3D dosimeters [radiochromic plastic (PRESAGE), radiochromic gel (FOX), and polymer gel (BANG)] for MR-image-guided radiation therapy (MR-IGRT) applications. In this work, for all three 3D dosimeter systems, the percent differences in responses with and without strong magnetic fields were minimal. These 3D dosimeters thus seemed applicable to MR-IGRT without requiring a correction factor.