A system and method for the measurement of radiation emitted from an in-vivo administered radioactive analyte. Gamma radiation sensors may be used to determine the proper or improper administration of a radioactive analyte, and identify patient administration factors that correlate with improper administration over a set of patients so as to identify administration risk factors to improve administration of radioactive analyte. In some cases, the system employs a sensor having a scintillation material to convert gamma radiation to visible light, which enables embodiments of the sensor to be ex vivo. A light detector converts the visible light to an electrical signal. This signal is amplified and is processed to measure the captured radiation. The sensor enables collection of sufficient data to support separate application to predictive models, background comparisons, or change analysis.