The present invention relates to the generation of an Atomic Therapeutic Indicator (ATI) for a test sample by the quantification of manganese; in voxels of a 3D region of the sample, wherein the 3D region is topographically defined by co-ordinates X′×Y′×Z. The ATI is used to assess the radio-responsiveness i.e. sensitivity or resistance to radiation treatment, of a cancer i.e. a tumor/neoplasm. In a preferred embodiment, the present invention relates to a method of generating the ATI, assessing the radio-responsiveness of a tumor/neoplasm based on the ATI and, based on the assessment, either treating or not treating the tumor with radiation. The present invention also relates to a method of determining if a cancer is likely to reoccur post radiation treatment comprising quantifying the level of manganese in voxels of a 3D region of a test sample from the cancer and determining the frequency of high metallomic regions (HMRs) in the cancer, wherein a high frequency of HMRs is indicative that the cancer is likely to reoccur and a low frequency of HMRs is indicative that the cancer is unlikely to reoccur; and associated methods of treatment.