Limitations of diagnostic reference level (DRL) and introduction of acceptable quality dose (AQD).

It is normal for a patient undergoing a radiological examination to expect that the radiation dose he/she will receive will be within a reasonable range of standard. Do we have that “standard” dose? The precise answer is actually no. The most common approach has been to use diagnostic reference level (DRL), which is a 75th percentile of the mean doses for a sample of patients close to the standard size, typically 70 kg or, in some countries, 60–70 kg. The purpose in cases of DRL is to detect outliers (higher 25th percentile cases) from a sample. In the absence of a standard dose, there has been an erroneous tendency to assume that being below DRL means adequate optimization.1 Removing rotten pieces of fruit is different from picking good pieces of fruit. DRLs do not provide guidance on what is achievable with optimum performance. DRLs were not developed as a tool for optimization within 75th percentile. DRLs provided good tools in previous years when the spread of doses were by a large order of magnitude and the shape of dose distribution curve was right-skewed asymmetric. There is no problem with DRL but stopping at DRL and using DRL in ways it was not supposed to be used creates problems.