SRP Comments on the ICRP Draft Tissue Reaction Report dated January 2011.
This document has the potential to be a significant contribution to the understanding of the biological effects of ionising radiation or in the field of radiation protection philosophy. However, it fails to deliver in either area because the document is not clear which area it is addressing. Is the document a review of the underlying science, or is it a review of dose limits and radiation protection philosophy?
The abstract and introduction fail to clarify what is intended, and as such meaningful comments are difficult to make. Indeed, even the draft title of the report, which extends over 3 lines of text, illustrates a lack of clarity of thought.
This problem is further illustrated in relation to discussions concerning cataract formation and threshold doses. Section 2.6.2 at page 102 indicates that formerly cataract formation was seen as a deterministic effect with a high threshold, but that there was now evidence indicating cataract formation was a stochastic effect without threshold. Section 4.7 at page 277 seems to say exactly the opposite. Nowhere in the document is there a clear statement on how cataracts should be considered.
As a review of the science, this apparent inconsistency can be accepted as part of the debate leading to clarification of the situation. However, a clear statement on which effect is favoured, or a clear statement that there is insufficient evidence to chose, is required.
When considering the underlying radiation protection philosophy, this degree of uncertainty is far less acceptable. Despite this, even though the thinking regarding cataract formation is unclear, the document takes the very brave step of indicating changes in the dose limits may be required. Clearly, this step is NOT justified on the strength of this confused document.
There are further objections on the way these potential “new” effects are being integrated into radiation protection philosophy. Based on the far from certain possibility that cataract formation is a stochastic effect, there is a proposal for a significant reduction in the dose limits.
This recommendation seems to be based on the existing concept that stochastic effects have a detriment that must be minimised. However, in the definitions to this document, detriment is defined in terms of fatal and non fatal cancer effects – detriments that are severe for the person concerned and costly to society. Cataracts, however are not fatal, easy to treat and, although there is a cost to society, that cost is small compared to the costs related to cancer.
There has been no attempt to review detriment in relation to cataracts before suggesting an ill advised reduction in dose limits. In suggesting this, ICRP seem to have ignored their own concept that doses should be as low as reasonably achievable, SOCIAL AND ECONOMIC FACTORS BEING TAKEN INTO ACCOUNT. No evidence is presented on social and economic grounds to support any proposed reduction in dose rates. No evidence is provided that show levels of cataract currently found in society are unacceptable and that there is a requirement on cost grounds to reduce the incidence of cataract.
Given these problems, it is recommended that ICRP fundamentally revise this document so that the issues of a science review and a consideration of underlying radiation protection philosophy are separated. Indeed, it is suggested that the report confine itself to a review of the science rather than addressing the philosophy, as it appears from the current document that the science is not yet clear enough to allow a consideration of dose limits. Dose limits and underlying radiation protection philosophy should be considered at a much later date, once the scientific matters are clear.
S M Clark
SRP Legislation and Standards