Thank you for the opportunity to comment on the ICRP document for managing patient dose in multi-detector computed tomography (MDCT). These are the comments of the United Kingdom Ministry of Defence. General comments In general the document provides a useful technical description of MDCT and the various parameters and factors which affect patient dose and the ways that patient dose can be reduced. The use of diagrams illustrating points that are being made in the text certainly improves clarity and understanding. Specific comments Summary – It would be helpful if the summary points were grouped by the chapters to which they refer. It would be helpful to have a list of abbreviations at the start of the document as there are a lot of different abbreviations used in the text. Line 158 We would question ICRP’s view that there should be joint responsibility between the requesting clinician and the radiologist. We believe that there are separate roles and responsibilities for the clinician and the radiologist which should be reflected in this document. The responsibility for the care of the patient and hence the choice of the procedure to be undertaken should be that of the person requesting the examination e.g. the clinician. However, he/she should seek the opinion of the expert as to the most effective imagining examination. This will be the specialist health professional, normally the radiologist, who should have adequate training and expertise in all medical imaging modalities. The specialist health professional has a responsibility to confirm that the imaging sought is appropriate for the purpose and suggest alternatives if a better outcome will result for the patient. This may be in terms of improved diagnostic power in relation to dose delivered (justification and optimization), to offer the best interpretation of images obtained and to discuss with the clinician when uncertainties arise. Clearly there is a need for close cooperation between all those involved. Lines 343 - 345 A simple diagram to explain the principle of pitch would be useful here – especially as it is a fundamental parameter that reoccurs later in the document. Lines 411 - 415 It would be useful to aid understanding to include examples of what is considered medically appropriate and what is medically questionable. Lines 500 - 507 A statement indicating whether manufacturers have now implemented this definition of pitch would help users decide if re-interpretation of equipment settings is required. Line 623 What are the new tools from manufacturers to tailor exposure factors? Are they software based or hardware/equipment? More detail would be appreciated. Lines 1298 – 1302 There are circumstances where there is a need to identify foreign/unwanted pieces of metal in the body e.g. shrapnel. Therefore it is important that machines are not all designed to eliminate streak artefacts. Lines 1385 – 1389 There will be circumstances where the patient is not conscious and there is no next of kin immediately available yet a decision on MDCT has to be taken quickly to save life. Therefore it is important that although this paragraph may recommend informed consent of radiation risks it should recognise such situations. Lines 1595 – 1600 As there may be occurrences where non-radiation based or low-radiation dose imaging techniques are not available and MDCT may be the only option. Therefore although alternative techniques should be recommended the use of MDCT must not be excluded.