ABSTRACT
Perhaps the most measured metric of beam quality is the half-value layer (HVL). The first and second half-value layers (HVL1 and HVL2), together, give a good indication of the penetrative characteristics of an x-ray beam. It is straightforward to obtain estimates of HVLs using the spectrum calculation software discussed in this book. When predictions do not agree with expectations, however, it is often troublesome to identify the source of the problem: is it the measurements, the spectrum model, or the input selections for the model that are at fault? This chapter discusses the issues to consider when predicting or matching beam-quality metrics such as half-value layer and illustrates the points with a comparison of the predictions of a spectrum model (SpekPy V2) to measurements by three Primary Standards Dosimetry Laboratories.
