Computed Tomography Dose Assessment - A Practical Approach

Abstract

A survey of the pattern and frequency of computed tomography (CT) examinations in Sweden has been conducted covering 89 of the 90 existing CT scanners (in 1991). The radiation output and the absorbed doses in phantoms have been measured for all types of CT scanners. For the assessment of the effective dose to the patient a new, practical approach has been developed. The average absorbed doses measured in cylindrical PMMA phantoms were assumed to be valid also for patients, those in the 320 mm diameter phantom for the trunk region and those in the 160 mm diameter phantom for the neck and head. With guidance from the ICRP 60 concept of tissue weighting factors, average weighting factors were adopted for the trunk, the neck, and the head region. Effective patient doses were calculated using three factors for doses measured in phantoms with the settings of exposure parameters as recorded in the survey. The results were compared with dose evaluations based on Monte Carlo calculations. The agreement was found to be satisfactory. It is suggested that this new practical approach should be adopted as a standard method for the assessment of effective dose in CT practices thus enabling direct access to dose evaluations in daily clinical practice - a prerequisite for the implementation of radiation protection concepts into the radiological society.