The Medical Dosimetry Group (MDG) in UKHSA focuses on radiation doses to patients in diagnostic imaging (planar X-rays, dental, computed tomography (CT), fluoroscopy and interventional).

The core work is to benchmark the doses used for diagnostic x-ray examinations nationally, and to calculate typical organ doses and effective doses for these exams.

National dose audits are undertaken in specific modalities looking at the more common examinations and those with higher dose. From these national dose audits, benchmark values, National Diagnostic Reference Levels (NDRLs), for different clinical examinations are established; quoted in units of dose index as given by the different types of diagnostic imaging systems. NDRLs support the implementation of the UK IRMER legislation.

The Medical Dosimetry Group also facilitates the NDRL Working Party, which consists of representatives from a number of organisations. The NDRL Working Party ensures a consistency of approach to the establishment of NDRLs and also facilitates a process to enable results from other, professional body run, national audits to be incorporated into the UK NDRL list.

Calculations of organ doses and effective doses are undertaken via general purpose Monte Carlo simulations. This work is primarily in computed tomography. For further information see dosimetry for patients.

Typical dose index values, such as dose length product (DLP), together with Monte Carlo calculated dose conversion coefficients give rise to a typical effective dose for the examinations reviewed.

When the frequency of examinations is incorporated, a population dose estimate from diagnostic x-ray examinations can be established. These are fed through to the UKHSA review of population dose.