Diagnostic Reference Levels in Medical Imaging

Draft document: Diagnostic Reference Levels in Medical Imaging
Submitted by Carmel J. Caruana, Medical Physics Department, University of Malta
Commenting as an individual

Thank you for this document. I would like to make some generic comments:

1. Although it has been noted within the document, it is important to emphasize and emphasize again within the same document that adherence to DRLs does NOT mean an optimised service (a legal requirement). It only means an assessment of how one stands with respect to other institutions; hence, if the institutions in a region are all overdosing then one''s levels would appear OK even though they are not really optimised. There is an attitude making the rounds of the sort "our levels compare well with so-and-so''s DRLs therefore everything''s ok....". Most radiology department managers only offer lip service to radiation protection and if they are below DRLs then it''s a perfect excuse not to carry out any real optimisation or ''policing'' of the service, since this obviously comes at a cost.

2. I am not sure whether the median is an appropriate quantity. Distribution of a cohort of patients with respect to dose is usually lognormal (like most physiological variables and dose follows physiological variables such as girth etc) and therefore the geometric mean might be more appropriate. The median may hide high values, the geometric mean does not.

3. Although the use of ANTHROPOMORPHIC phantoms (the "Atom'' type not simply blocks of tissue equivalent material) is being discouraged in the establishment of DRLs (so that measured values would also include unacceptable variations in operator performance) it is important to emphasize within this document that such phantoms are still crucial for real protocol optimization studies involving measurement of actual absorbed doses and image quality. This is particularly true in the establishment of new protocols, commissioning of equipment etc

4. It is important to also emphasize that reducing radiation dose to a level below a DRL (just reduce the mAs!) without ensuring that the quality of the image is still sufficient for accurate diagnosis is not only unethical, it is also illegal.

5. The use of weight for establishing standard patient samples has been known to be problematic. There is so much literature on this that I fail to see why it has even been considered (except that it''s the easiest thing for the radiographers to measure) e.g., for abdo CT body shape varies so much (e..g, from North to South Europe, this is bould also to vary with change of degree of obesity with time) - girth has been found to be much more correlated with dose and hence much more appropriate.

Carmel J. Caruana
Medical Physics Department
University of Malta