Ionizing radiation can create stable free radicals in solids that can be quantified, in a nondestructive way, by Electron Spin Resonance (ESR) leading to a dosimetric technique. Ionizing radiation can change the valence of iron ions and the viscosity of certain polymers leading to changes in the relaxation times of protons, allowing the use o nuclear magnetic resonance imaging (MRI) to image three-dimensional dose distribution. Both techniques are expected to improve the quality of medical care that rely on the use of ionizing radiation. ©2001 American Institute of Physics.