Effective energy in diagnostic radiology. A critical review

The concept of effective energy, commonly used to characterise the photons in a roentgen beam exhibiting a distribution with respect to energy, is critically reviewed. Definitions are given in terms of equations which clearly demonstrate that values of effective energy depend on the physical quantity with respect to which they are calculated. Examples are discussed which quantify the errors which may result due to incorrect application of effective energy in deriving values for various physical quantities. For instance, the energy imparted to the patient in diagnostic radiology may be underestimated by as much as a factor of two.