Effective Doses from Diagnostic X-Ray Procedures

Abstract

It is useful to set into perspective the doses received from diagnostic medical procedures whenconsidering human exposure to low doses of ionizing radiation. The manner in which diagnostic x-raydoses are specified leaves confusion and makes their significance difficult to evaluate. On the onehand, the numbers may be quoted in terms of entrance skin exposure; on the other hand,knowledgeable radiation workers are accustomed to specifications in terms of effective dose. Thispaper discusses doses received from conventional diagnostic x-ray procedures in terms of effectivedoses and determines the effective doses for standard procedures from recent survey measurements ofmedical x-ray units.The conversion of the exposure data to effective doses requires a step wise approach. Firstly, exposuredata are converted into air kerma, then the absorbed doses to critical organs in the field of view aredetermined and, finally, the tissue weighting factors are applied to convert absorbed dose equivalents toeffective dose. A body-compartment model has been used in the apportioning of critical organs for thevarious fields of view in imaging procedures.We have applied the information in ICRP-74 to determine absorbed dose equivalents from air kerrnafor x-ray procedures. To simplify calculations we advocate the use of a compartment-weighting-factormodel in converting organ dose equivalents to effective doses for the respective diagnostic procedures.Compartment weighting factors have been derived from a Health Physics Society Standard preparedfor multiple badging of radiation workers.The objective of this discussion is to provide dose information for diagnostic x-ray procedures in termsof effective dose. In this way an appropriate comparison can be made with effective doses arising fromother activities and an assessment can be made of the role of diagnostic procedures in the discussion ofpotential low-dose effects. As an example, the average effective dose for a chest x-ray in ourjurisdiction is 0.02 mSv (2 millirem) corresponding to the average entrance skin exposure of 11.7 rnR( 1 997).