A critical appraisal is made of quantities and units in radiation protection work and a different approach is suggested for establishing permissible limits of radiation exposure. There is an ambiguity in the current health physics terminology, particularly with reference to such quantities as dose equivalent. It is pointed out that dose equivalent has been specified for a macroscopically small volume element w around a point r in a medium which can be a phantom or a human body. In such cases dose equivalent has been assumed to vary from one point to another; it is therefore a field quantity, representing a condition spacially distributed in a medium. There exists, however, another quantity erroneously called “dose equivalent” which is not a field variable but a single numerical entity. This other quantity, which for all practical purposes has remained anonymous, represents the “amount” of exposure and is related to what is known to be the maximum permissible dose (MPD). There is also confusion in speaking about the quality factor (QF). The name “quality factor” is currently used to represent several quantities, conceptually different one from the other, and the usefulness of some interpretations of the (QF) is open to question. It is shown that the relationship between the dose equivalent and the quality factor recommended by the International Commission on Radiation Units and Measurements (ICRU) is not that which is used in health physics calculations; there is therefore a discrepancy between the “official” and the “non-offcial” points of view. The assumptions which lead to the derivation of the quality factor and of other similar concepts are analyzed from an operational and more particularly from an instrumental point of view. It is pointed out that the requirements for radiation protection have not been adequately systematized and in order to give a more complete account of what is considered to be the responsibility of a health physicist, and alternative, anticipatory approach to the interpretation of radiation quality is presented. It is proposed that a “quality index” Q = Deeff/Dr be defined where Dr is the “reference dose” to be used in monitoring a radiation field and Deeff is the “effective dose equivalent” which is the name given in this analysis to the “amount” of exposure. The reference dose is expressed by the quotient of Er by mr, where Er is the energy imparted by ionizing radiation to the matter having “standard” chemical composition (approximating that of soft tissue) in a volume element vr and mr is the mass of matter in that volume element (Dr = Er/mr). Since radiation protection procedures are anticipatory, the measurements of reference dose should be made in an unperturbed radiation field, whereas the effective dose equivalent should be obtained from a perturbed field, the perturbation being produced by a phantom, introduced in a locale in which the measurement of the reference dose has been previously made. The suggested anticipatory point of view is intended to supplement rather than to replace the one in which “simultaneous” measurements are made, as with dosimeters and other instruments worn by workers in the radiation field.
©1970Health Physics Society