4 Conversion Coefficients

Conversion coefficients link the protection and operational quantities to radiometric and dosimetric quantities characterizing the radiation field. In practice, the quantity that is usually used or calculated in external radiological protection is the particle fluence, Φ, of a radiation type. In the case of photon radiation, air kerma free-in-air, Kair, is also used. Thus, effective dose, E, may be related to the fluence of a particle type by means of the appropriate conversion coefficient. An internationally agreed set of conversion coefficients for protection quantities is available for general use in radiological protection for occupational exposures in ICRP Publication 116 (2010). They are calculated for whole-body irradiation of phantoms in vacuo to broad uniform parallel beams assumed to represent occupational exposure for the following field geometries with antero-posterior (AP), posterior-anterior (PA), left lateral (LLAT), right lateral (RLAT), and to rotational (ROT), isotropic (ISO), superior hemisphere semi-isotropic (SS-ISO), and inferior hemisphere semi-isotropic (IS-ISO) fields. Conversion coefficients to effective dose are available for these ideal exposure geometries only.