European Union Council Directive 2013/59/EURATOM (2013) requires that nuclear medicine therapies are performed using treatment planning for individual patients based on dosimetry. The aim of this project is, therefore, to develop a compartmental model to describe the 223Ra distribution in the human body to better understand the underling mechanisms. Compartmental models of Radium in the literature have only been developed for healthy humans and animals. As part of this study, available compartmental models will be evaluated and a new compartmental model designed based on the findings in the literature. 223Ra is routinely used at the RMH and extensive data (activity retention measurements in the whole body, individual organs, blood, urine, and feces) has been collected as part of “Phase 1, Open-Label Study of the Biodistribution, Pharmacokinetics, and Dosimetry of 223Ra-Dichloride”. The newly developed compartmental model will be adapted to allow for a fit to the available dataset. Compartmental analysis will be performed using SAAM II v2.3, a well-established kinetic modelling software. The fit to the available dataset should allow for the determination of rate constants which can be compared to those rate constants of healthy humans.