A method for the ex vivo real-time determination over a period of time of one or more of the magnitude, location, and volume of radioactive material in the body by measuring radiation that decays in vivo emitted by a subject, the method comprising: (i) applying one or more ex vivo radiation measurement sensors proximate an area of interest on a patient; (ii) detecting radiation over a desired period of time and producing signal data associated with the desired period of time; (iii) amplifying the signal data using a signal amplifier in operable communication with the radiation sensor, wherein the measurement sensor has at least one sensor output for such amplified signal data, and outputting the amplified signal data; (iv) processing the amplified signal data using a computer processor in operative communication with a non-transient memory and the measurement sensor output by performing the steps of: (a) receiving the amplified signal data associated with the desired period of time; (b) comparing the amplified signal data to a set of expected signal data for radioactive sources of various magnitudes, locations, and volumes; (c) determining, based on the comparison of amplified signal data to a set of expected signal data for radioactive sources of various magnitudes, locations, and volumes, one or more of a magnitude, location, and volume of the radioactive source in the body over the desired period of time by fitting the amplified signal data to the most likely set of expected signal data. (i) applying one or more ex vivo radiation measurement sensors proximate an area of interest on a patient; (ii) detecting radiation over a desired period of time and producing signal data associated with the desired period of time; (iii) amplifying the signal data using a signal amplifier in operable communication with the radiation sensor, wherein the measurement sensor has at least one sensor output for such amplified signal data, and outputting the amplified signal data; (iv) processing the amplified signal data using a computer processor in operative communication with a non-transient memory and the measurement sensor output by performing the steps of: (a) receiving the amplified signal data associated with the desired period of time; (b) comparing the amplified signal data to a set of expected signal data for radioactive sources of various magnitudes, locations, and volumes; (c) determining, based on the comparison of amplified signal data to a set of expected signal data for radioactive sources of various magnitudes, locations, and volumes, one or more of a magnitude, location, and volume of the radioactive source in the body over the desired period of time by fitting the amplified signal data to the most likely set of expected signal data. (a) receiving the amplified signal data associated with the desired period of time; (b) comparing the amplified signal data to a set of expected signal data for radioactive sources of various magnitudes, locations, and volumes; (c) determining, based on the comparison of amplified signal data to a set of expected signal data for radioactive sources of various magnitudes, locations, and volumes, one or more of a magnitude, location, and volume of the radioactive source in the body over the desired period of time by fitting the amplified signal data to the most likely set of expected signal data.