A device of estimating a dose of ionizing radiation absorbed in an intra bone volume. The device comprises a static magnetic field source adapted to generate a substantially static magnetic field in a probing space having a volume of less than 2 cubic millimeter (mm3), the probing space being placed in front of a distal end of static magnetic field source, a micro resonator mounted in adjacent to the distal end, and at least one transmission line which feeds the resonator so as to generate an microwave magnetic field at the probing space and to transmit a signal returned from said microwave magnetic field and indicative of radiation induced paramagnetic defects in said probing space so as to allow a spectrometer to compute a dose of ionizing radiation absorbed in a portion of a bone placed in the probing space according to an analysis of the signal. The static magnetic field source being sized and shaped to maneuver the probing space to overlap with an intra bone volume of the bone.