Radiation Units, Limits and Dose Constraints
A number of radiation units exist for representing radiation dose to patients, staff, public and quantities for radiation equipment performance in radiological practice. What is important is how ably to communicate these to medical professionals. The concept of air kerma, a measurable quantity outside the human body has been recommended by the IAEA and ICRU (International Commission on Radiation Units and Measurements). From air kerma, one estimates the entrance air kerma on patient or other quantities such as CTDIw or CTDIv. Also the kerma area product (KAP) is useful quantity that is easily measured in particular in fluoroscopic procedures. The organ doses have direct relationship with biological effects and can be estimated from entrance air kerma. By using the tissue weighting factor, one estimates the dose equivalent and effective dose. In specific situation of interventional procedures, cumulative air kerma at interventional reference point has been described. Similarly there are quantities for staff dose estimation based on measurable values and estimation of dose equivalent and effective dose. There is a concept of dose constraint that is applied to carers and comforters of patients. This concept is also applied in occupational protection. Radiation dose limits are given for staff and members of the public, dose constraints for comforters and there are no dose limits for patients but the concept of diagnostic reference level applies. The lecture will cover these quantities, explain the role played by international organizations and discuss how they can be used in day-to-day practice in hospitals.