A survey of radiation doses to patients in five common diagnostic examinations. I. Principles and techniques of dose evaluation by indirect measurement II. Survey results

Abstract

Techniques for the determination of radiation doses to patients in diagnostic radiology are briefly reviewed. Attention is focused upon indirect methods in which measurements of X-ray output are made prior to the actual examination, thereby enabling the entrance skin dose to be calculated if radiographic factors are known. Indirect methods are compared with direct methods which involve TLD measurements on the patient. For certain examinations involving automatic exposure control, and in fluoroscopy, retrospective simulations of the examination or direct methods may be used to supplement the calculations. In order to appreciate the significance of inter-hospital variations, the “speed” of an X-ray imaging system is quantified in terms of the “speeds” of individual components of the imaging chain such as tube potential, film-screen speed, grid attenuation and the performance of the automatic film processor. These “system speed factors” (SSF) may be multiplied together to give a combined SSF which indicates the relative efficiency with which a particular X-ray imaging system utilises the X-ray flux incident upon the patient.