The Operational and Protection Quantities for External Radiation Exposure: A review

The concepts of protection and operational quantities are fundamental in radiation protection, essential for assessing and controlling exposure to ionizing radiation. Protection quantities are designed to reflect the risk of stochastic health effects resulting from radiation exposure. However, these quantities cannot be measured directly, as they depend on knowledge of the energy deposited in organs and tissues, as well as the biological sensitivity of different tissues. To address this gap between theoretical risk assessment and practical measurement, operational quantities were introduced. These serve as practical surrogates that conservatively estimate protection quantities under specific exposure conditions. In the context of external radiation exposure, it is crucial to evaluate the effects associated with the radiation exposure processes to ensure adequate protection for workers, members of the public, and healthy parts of patients. For this purpose, the International Commission on Radiation Units and Measurements (ICRU) and the International Commission on Radiological Protection (ICRP) have provided definitions and phantoms for protection and operational quantities in reports such as ICRU-57 (1998) and ICRP-74 (1997). Furthermore, the ICRU-95 (2020) report suggests a different approach to defining operational quantities, based on the same phantoms used for defining protection quantities, making them good estimators of protection quantities. This research provides a summary of the definitions and phantoms for both protection and operational quantities. Understanding the relationship between operational and protection quantities is essential for ensuring accurate monitoring and control of radiation exposure. Therefore, this study presents definitions for radiometric and dosimetric quantities, as well as their relationships. Additionally, comparisons between protection and operational quantities are discussed, drawing on all relevant ICRU and ICRP reports.