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′xY′xZ. The ATI is used to assess the radio-responsiveness i.e. sensitivity or resistance to radiation treatment, of a cancer i.e. a tumour/neoplasm. In a preferred embodiment, the present invention relates to a method of generating the ATI, assessing the radio-responsiveness of a tumour/neoplasm based on the ATI and, based on the assessment, either treating or not treating the tumour 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.The invention further relates to a method of determining the radio-responsiveness of a melanoma, the method comprising determining the level of melanin in a test sample from the melanoma, wherein the lower the level of melanin the more sensitive the melanoma is to radiation and the higher the level of melanin the more resistant the melanoma is to radiation; and associated methods of treatment.