Dose descriptors for computed tomography

A weakness in the dose descriptor, the computed tomography dosimetry index, is discussed and an alternate descriptor is proposed. The new descriptor, the equivalent rectangular width, conveniently expresses the spatial spread of dose and is simply derived from customary dose measurements. A measure of performance, which expresses the relative size of the volume being imaged with respect to the volume receiving the dose, is suggested for computed tomography. 87.70.Es, 87.60.Mv.