Radiation Dosimetry: Formulations, Models, and Measurements

Abstract

As measurements of doses received by internal tissues of the body cannot be made, internal dose estimates must be performed via calculations and the use of theoretical models. Standardized models of the human body, and often standardized models of radiopharmaceutical behavior in the body, are employed to describe and predict the radiation doses received by various tissues in the body. The use of agreed-upon standardized models will result in calculations that are traceable and reproducible, but one must bear in mind that calculated dose estimates are only as good as the input assumptions and models employed as input to the calculations. One must also remember that these calculated doses are doses to a model, not a patient. In diagnostic applications, this is generally acceptable. All input data has some associated uncertainty, and the calculated results reflect the inherent uncertainty in the data as well as those related to the application of standardized models of the body to a variety of patients who vary substantially in size, age, and other physical characteristics (this subject is discussed in detail later in this chapter). When the radiation doses are relatively low, this kind of uncertainty is tolerable, because if calculated answers are not entirely accurate, the consequences for the patient will be small or even nonexistent (depending on what one believes about radiation risk at low doses and dose rates). In therapeutic applications, however, more attention to accuracy and precision is needed, as with these higher doses, the chances of reaching or exceeding an organ’s threshold for expressing radiation damage are more significant.