The central dose quantities used in radiological protection are absorbed dose, equivalent dose, and effective dose. The concept of effective dose was developed by the International Commission on Radiological Protection (ICRP) as a risk-adjusted dosimetric quantity for the management of protection against stochastic effects, principally cancer, enabling comparison of estimated doses with dose limits, dose constraints, and reference levels expressed in the same quantity. Its use allows all radiation exposures from external and internal sources to be considered together and summed, relying on the assumptions of a linear non-threshold dose-response relationship, equivalence of acute and chronic exposures at low doses or low dose rates, and equivalence of external and internal exposures. ICRP Publication 103 provides detailed explanation of the purpose and use of effective dose and equivalent dose to individual organs and tissues. This publication provides further guidance on the scientific basis for the control of radiation risks using dose quantities, and discusses occupational, public, and medical applications. It is recognised that best estimates of risk to individuals will use organ/tissue doses and specific dose risk models. Although doses incurred at low levels of exposure may be measured or assessed with reasonable accuracy, the associated risks are increasingly uncertain at lower doses. Bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, it is concluded that effective dose may be considered as an approximate indicator of possible risk, recognising also that lifetime cancer risks vary with age at exposure, sex, and population group. A further conclusion is that equivalent dose is not required as a protection quantity. It will be more appropriate for limits for the avoidance of tissue reactions for the skin, hands and feet, and lens of the eye to be set in terms of absorbed dose rather than equivalent dose.
Following the issuance of new radiological protection recommendations in Publication 103 (ICRP, 2007), the Commission released, in Publication 110 (ICRP, 2009), the adult male and female voxel-type reference computational phantoms to be used for the calculation of the reference dose coefficients for both external and internal exposures. While providing more anatomically realistic representations of internal anatomy than the older stylised phantoms, the voxel phantoms have their limitations, mainly due to voxel resolution, especially with respect to small tissue structures (e.g. lens of the eye) and very thin tissue layers (e.g. stem cell layers in the stomach wall mucosa and intestinal epithelium). This report describes the construction of the adult mesh-type reference computational phantoms (MRCPs) that are the modelling counterparts of the Publication 110 voxel-type reference computational phantoms. The MRCPs include all source and target regions needed for estimating effective dose, even the m-thick target regions in the respiratory and alimentary tract, skin, and urinary bladder, assimilating the supplemental stylised models. The MRCPs can be directly implemented into Monte Carlo particle transport codes for dose calculations, i.e. without voxelisation, fully maintaining the advantages of the mesh geometry.
This report describes the development and intended use of a series of ten computational phantoms representing the reference male and female at newborn, 1-year-old, 5-year-old, 10-year-old, and 15-year-old as defined in Publication 89. These phantoms have been formally adopted by the ICRP for use within ICRP Committee 2 in the development of age-dependent dose coefficients following the 2007 Recommendations. They are presented in this report in the very same voxelised structures and tissue ID numbers as given in Publication 110 for the adult reference computational phantoms. These paediatric phantoms have been used by Task Group 90 of ICRP Committee 2 in the development of age-dependent dose coefficients representing external exposures to contaminated air, water, and soil. They have also been used by Task Group 96 of ICRP Committee 2 in the development of age-dependent specific absorbed fractions for internally emitted photons, electrons, alpha particles, and neutrons, in a manner similar to the adult SAF (Specific Absorbed Fraction) values given in Publication 133.
