**Abstract**

Adequate understanding of radiopharmaceutical distribution in the body of the patient has both spatial and temporal characteristics and they are the key factor to consider when planning successful radio pharmaceutical therapy, because they are an integral part of the radiation dosimetry calculations of any proposed personalized treatment. In this chapter we will focus on radioiodine therapy for thyroid cancer patients since it is a widely known practice in clinical oncology. Factors affecting the radioiodine organs' distribution will be examined in sufficient details using the available published research in the scientific literature. The literature will be reviewed extensively and summarized in this chapter. Another aim is to provide the medical practitioners with a quick reference guide to this clinically important area of expertise; often mastered by medical physicists with background in radiation physics, mathematics and medical imaging analysis. This chapter will cover recent advances in the area of radioiodine biodistribution modeling with applications in preclinical and clinical studies.

**Keywords:** radioactive iodine, biodistribution, clinical applications, recent advances
