This is a welcome document. Thank you for the hard work in putting it together.
Below are comments from the Medical Sector Committee of the Society for Radiological Protection in the United Kingdom.
Section 1.6, paras 33 & 34, page 26
The concept of ‘Achievable Dose’ is much more readily understood than DRLs, so is to be welcomed in this document. However, after explaining the concept in paras 33 & 34, para 35 then reverts to the much more complex phrase “median value of the distribution of a DRL quantity observed in a survey of healthcare facilities”. It has been suggested that using ‘Achievable Dose’ here and throughout the document would improve and simplify the understanding of the text.
Section 1.6, para 35, page 26
Paragraphs 33 & 34 define ‘Achievable Dose’ as the “median value of the distribution of a DRL quantity observed in a survey of healthcare facilities”, whereas paragraph 35 appears to use the same definition to describe “an additional value specified that would serve as a simple test to identify situations where levels of patient dose are low and investigation of image quality should be the first priority”. One can’t have an achievable dose and a trigger for situations where the dose might be too low set at the same value!
The idea of combining an Achievable Dose (a dose for a group of patients that one might expect to be able to achieve), coupled with a DRL (a dose that one would not be expected to exceed), might be a way to proceed, but one couldn''t see this explained as simply as this anywhere in the text.
Section 2.1, para 49, page 34
The document refers to comparison of local data with a DRL as being the ''first step'' in optimisation. It has been commented that this ought to be the ''last step''. Here''s the main issue that some people have with DRLs - they are derived using an arbitrary cut- off in the ranking of mean (or median) doses from a wide range of practices, over a wide geographical area, using a broad range of equipment types. However, one does not know which, if any, of these doses are ''optimised''. It has ben argued that ideally, the ''first step'' in optimisation should be to set up the system optimally before use and subsequently keep it there. In this case, one should be using an internal reference point, not an external one. A statistical process control approach, similar to the way one monitored processor temperature in the old days, would be much more sensitive to local change. Essentially, in an ideal situation, one should get it right to start with, balancing adequate image quality with lowest reasonably achievable dose, then monitor the dose continuously, or periodically, to make sure it doesn''t wander too far off. The statistical criteria for determining the threshold for triggering action will use data generated from the same equipment. Once we are all getting it right, using the most dose-efficient equipment in the most dose-effective way, there should be quite a narrow distribution of median doses across facilities, in which case it would not matter very much precisely where a facility sits in that distribution. The data reported by Sutton, referenced as ‘Sutton 2014’ appears to demonstrate that this has indeed happened in this particular situation.