SRP response to the ICRP consultation on the use of Effective dose
SRP believes that the proposed changes in the ICRP document are reasonable and pragmatic from an occupational dosimetry perspective. SRP agrees with ICRP that deterministic radiation-induced health effects should now be measured in the quantity of radiation absorbed dose in Gray rather than in the quantity of equivalent dose in Sievert. However, a practical implication of such a change in ICRP recommendation is that some may consider that international standards may need to be updated at a time when these standards have yet to be fully implemented internationally. SRP notes that, in lines 1970 to 1973 of the draft report, the Commission makes clear that the report’s recommendations would not be formally published in advance of its publication of new general recommendations on radiation protection matters in due course. SRP strongly supports this position both from the standpoint of maintaining confidence by stakeholders in the international standards and the current radiological protection framework.
One issue that has not been addressed is the retrospective calculation of organ/tissue ‘doses’ for compensation scheme / litigation purposes (and possibly also relevant for epidemiology studies). In such cases the end point is often to derive a dose relationship to a diagnosed cancer in a specific organ/tissue; in such cases the use of Absorbed Dose would not be appropriate, and Equivalent Dose (or some similar quantity which retains a radiation-weighting factor) would still be more appropriate (ie the incidence of biological/clinical effect is of a stochastic from rather than deterministic).
SRP note that some believe that over the years ICRP has sometimes been guilty of change for change sake. With average annual occupational doses being steadily reduced (typically less than 2 mSv) is a change to Gray really necessary and might it undermine public confidence in the system of radiological protection?
The main advantages of the use of effective dose and Sieverts were that it allowed the addition of assessed doses from various sources eg internal, external and individual organ doses in some sort of logical fashion, and that it allowed some account to be taken of risk and lifetime risk. The main disadvantage being that you can't measure Sieverts directly in metrology terms.
There is of course always the option for regulatory authorities to continue to set dose limits in Sieverts if ICRP choose to recommend constraints or similar in Gray?
With regard to eye lens SRP notes that the cause and effect to the eye lens has to be primarily a Deterministic effect. Although arguments are made to apply dose as Stochastic for the eye lens this is primarily based on use or application to Occupational Exposure. ICRP should make this argument transparent. This would help with control for occupational dose limits as now applied in Legislation for Work with Ionising Radiation. Noting there is no weighting factor for the eye lens. ICRP then need to comment on a difference between occupational exposure and emergency exposures in relation to setting dose limits and the appropriate quantity to use in both situations. Clearly should there be an emergency exposure (to an operator, responder or member of the public) this is most likely a one off lifetime occurrence (unlike that for occupational exposure). ICRP would help to comment on appropriate dose quantity and limits to use for the eye lens in an emergency to differentiate between what are two different types of situations and consequences to those exposed to ionising radiations where the dose to the eye lens could be used for both Deterministic and Stochastic parameters.
We note the detailed additional comments from Sellafield Limited and our member Graham Smith.
Additionally we endorse the comments of the IRPA.