Appendix D: Internal Dosimetry

Abstract

IntroductionInternal dosimetry can be overwhelming and sometimes confusing because there is a wealth and diversity of models and terminology. International Commission on Radiological Protection (ICRP) and Medical Internal Radiation Dose (MIRD) methodologies are the most commonly used internal dosimetry models. The various ICRP and MIRD models are similar in terms of their assumptions and defining equations. This similarity is obscured by difference in the terminology and notation. These differences contribute to the confusion and can limit a full understanding of these models. Emphasizing the definition of absorbed dose and using this definition to illustratethe terminology andnotation of theMIRDandICRP minimize theconfusion.Contemporary internal dosimetry models began with the single-compartment models of ICRP 2 and 10 (ICRP 2/10). The MIRD methodology and ICRP 26 and 30 (ICRP 26/30) developed the concept of source and target organs. ICRP 60 and supporting publications, including ICRP 66 (ICRP 60/66), continue to refine the internal dosimetry methodology. In this appendix, we use the notation ICRP 2/10, ICRP 26/30, and ICRP 60/66 to refer to the defining internal dosimetry publications and supporting documents. Additional refinement is planned as a part of the 2007 ICRP recommendations and supporting publications.In this appendix, the essential elements of internal dosimetry are presented. The presentation begins by defining the key elements of the MIRD and ICRP models in terms of the absorbed dose. With the key elements established, the MIRD and ICRP methodologies are presented in additional detail. D.2 Overview of Internal Dosimetry ModelsAs an introduction to the MIRD and ICRP internal dosimetry models, the absorbed dose rate following the intake of radioactive material is calculated. If an isolated (single-compartment) organ having a mass m contains an activity q(t) of radioactive Health Physics in the 21st Century.