|Dose Constraints and topical issues on the new draft ICRP recommendations (S.H. NA, KINS)
Even though there is no time for extension of full consultation, the following comments are submitted on behalf of the Korean Association for Radiation Protection.
The ICRP¡¯s elaboration to clarify the meaning and use of the concept of constraints is an improvement from the previous draft, however its complexity to implement and burden to take the legislatorial actions is still remained for further tasks, which may cause negative response against the concept of constraints.
Our group feels that further development is needed for the concepts of Constraints in conjunction with the Single Source: the term of ¡°constraint¡± is repeated more than 170 times in the draft and this causes confusion; the practice of release from a site of nuclear power plants may considered as a single source however it is not clear for the case of adding or decommissioning a reactor at the same site. How about a moving source, which has been taken into account as the group of single source practice ?.
Regarding the subject of cancer and hereditary effects, the uncertainties of the use of LNT should be described in balance without biasing in favor of the proportionate relationship between increments of dose and risk. Some scientific facts of epidemiological study or some pilot survey results need to be described to harmonize the balance of evidence, which will show the difference contrast in increment of cancer and hereditary effects among the population living in significantly high natural radiation background comparing to the normal.
The description of Diagnostic Reference Level is appropriate, however, the warning of potential risk increment from unreasonable diagnostic medical exposure needs to be added especially for impractical repetitions of PACS (Picture Archiving Communication System) in the hospital: the radiation exposure for the health care check is increasing and it causes the expansion of normal public exposure. Can we keep this exposure aside without comments when we deal with the occupational exposure which does not show much contrast.
Biological Aspects of Radiological Protection (Para. 44-87)
3.2. The induction of cancer and hereditary effects
The term of Low Dose does not express clear picture below the value of 100 mSv above which will produce a directly proportionate increment in the detrimental effects attributable to radiation (LNT). When this value is used in the frame of radiation protection it is a dose limit value, which means that it is Low Dose Exposure if an individual dose is lower than the limit (Para. 55-56):
Refer to low individual, extremlely low, trivial, very low in Para 146-148.
Remove the term of Low from Para 55 and editorial in relation in Para. 56 and 146-148.
The clarity of the use of collective dose and the new approach to estimate hereditary risks accounted two generations of human body resulted in decreased values and this reduction is agreed upon in the fact of no direct evidence that exposure of parents to radiation leads to excess heritable disease in offspring. Regarding the judgement of exclusion of the concept of Equilibrium Generation from the methodology, it should not be allowed to bring it back into consideration again in future.
In a practical sense, the shape of the linearity of relationship or the threshold of dose effect is not a major problem. The problem is, however, that the LNT hypothesis brings the major cause of the concern to the general public by perceiving that radiation is harmful no matter how low the dose is. To get rid of this misunderstanding ICRP should clearly mention that LNT hypothesis does not reflect the actual effects of radiation but a tool for radiation protection/control.
Regarding the uncertainties of dose response at low doses/dose-rates for cancer and heritable effects, they need to be balanced without biasing in favor of the proportionate relationship between increments of dose and risk. Some scientific facts of epidemiological study or some pilot survey results need to be described to harmonize the balance of evidence, which will show the difference contrast in increment of cancer and hereditary effects among the population living in significantly high natural radiation background comparing to the normal.
Adaptive response or hormesis
Adaptive response or hormesis surely would reduce the risk from low dose radiation. However, we know that these protective phenomena depend on the genetic background; these responses may differ from one individual to another. Before we understand the mechanism underlying the adaptive response/hormesis, it should be difficult, at present, to take them into the framework of radiation protection.
Comments to the Draft Recommendation
The radiological protection policy should protect people from the potential risk from radiation; also, it should never give an unreasonable concern or fear to the general public. Due to the LNT hypothesis the general public tends to believe that ionizing radiation is harmful no matter how low the dose is. Therefore, the Commission should clearly mention that the LNT hypothesis is a tool for radiation protection and is not a description of the actual risk from ionizing radiation of low doses. In this sense, it is
Appreciated that the paragraphs 57,143,and 147 describe the caution for inappropriate use of the LNT hypothesis it self, and effective dose and collective dose, which are based on the LNT hypothesis. However, the caution should be added in the paragraph 54, where the appropriateness of LNT hypothesis is claimed. It should be helpful for the understanding the situation to add examples showing no significant increase in risk at low dose range, e.g. epidemiological study in high natural background radiation.
Add scientific facts of epidemiological study or some pilot survey results to harmonize the balance of evidence, which will show the difference contrast in increment of cancer and hereditary effects among the population living in significantly high natural radiation background comparing to the normal.
Constraints and Single Source
The concept of Constraint is or will be useful therefore further clarification is needed to include the following:
- Definition of Single source for the cases of adding new NPPs at the existing NPP site, occupying more than one institute at a single site NPPs, etc.
- Develop the senarios to assign the constraint value to single source or the specific values, otherwise it will be the burden to the Authority.
- The concept should be implemented inside the principle of radiation protection described in the draft for example, Justification, Optimisation, Limitation, Constraints as well as Exclusion and Exemption.
- The case of existing exposure and patient release should be clarified.
- Benchmarking test or pilot examination is required before implementaion
It should not be confused with the complementary requirement to optimize the level of protection. The Commission has previously recommended in its system of protection for practices that the optimisation process should have restrictions on the doses to individuals, termed dose constraints, in order to reduce inequities inherent in the optimisation process. --- Para192-198:
- Clarify the vagueness between Optimization and Constraints and their functions within the radiation protection in conjuntion with Para 159.
- Constraints defined in planning stage should not be used for other practice as stated in the last sentence of Para 197, which is conflicted with Para 174.
The principle of optimisation of protection is the selection of an appropriate value for the dose constraint ---- : potentially misleading in implementation.
- Rewrite (210) to avoid misinterpretation (editorial)