1. The current system of radiological protection based on the Linear No-Threshold (LNT) hypothesis has greatly contributed to the minimization of doses received by workers and members of the public. However, it has brought about gradiophobiah among people and waste of resources due to over-regulation, because the LNT implies that radiation is harmful no matter how small the dose is.
2. Now that the existence of bio-defensive mechanisms such as DNA repair, apoptosis and adaptive response are well recognized, the linearity assumption cannot be said to be gscientifich. Evidences increasingly show that there are threshold effects in risk of radiation.
3. Radiation protection professionals do not need to convince scientists; they need to convince ordinary citizens who are afraid and worried and who want to judge and decide for themselves.
Ordinary adult members of the public understand the statement gLow doses of radiation are safeh. They do not understand comparative risk. All they want to know is if radiation is safe or not. They know that nothing is absolutely safe and they donft expect anything to be.
4. The US Health Physics Society updated its position statement in 2004, in which the Society recommends against quantitative estimation of health risks below an individual dose of 5 rem (50 mSv) in one year or a lifetime dose of 10 rem in addition to background radiation, because below 10 rem, risks of health effects are either too small to be observed or are non-existent.
5. A concept of gpracticalh thresholds or gvirtually safe dosesh will have to be introduced into the new system of radiological protection in order to resolve the low dose issues. gPracticalh thresholds may be defined as dose levels below which induction of detectable radiogenic cancers or hereditary effects are not expected. If any workers and members of the public do not gain benefits from being exposed, excepting intentional irradiation for medical purposes, their radiation exposures should be kept below gpracticalh thresholds.
Specific comments on the FD-C-1
1. Principal Conclusions and Proposals of the Task Group
Draft (lines 188-190): For cancer and hereditary diseases at low doses/dose rates the use of a simple proportionate relationship between increments of dose and increased risk is a scientifically plausible assumption.
gscientifically plausibleh should be deleted from the sentence above, because a simple proportionate relationship is not scientifically justified but just an assumption.
3.1.1 Definition of stochastic effects and tissue reactions
As there is a remarkable similarity between so-called gstochastic effectsh and gtissue reactionsh, it seems reasonable to classify adverse health effects of ionizing radiations into the following two categories for the purpose of radiation protection:
1. Somatic effects; early and late effects (including cancer)
2. Genetic (Hereditary) effects
Descriptions of gtissue reactionsh can be applied to gstochastic effectsh as shown below.
(1) Draft (lines 853-856) for tissue reactions:
Now it is recognized that both early and late tissue reactions are not necessarily predetermined, and they can be modified after irradiation by the use of various biological response modifiers.
Proposed description for stochastic effects (lines 830-831):
Modifications in single cells with genetic changes or transformations leading ultimately to malignancy are not necessarily predetermined, and they can be modified after irradiation by the use of various biological response modifiers.
(2) Draft (lines 845-847) for tissue reactions:
In order to reach the level of detection, a given proportion of cells must be depleted. This constitutes a threshold, which depends on the specified level of injury.
Proposed description for stochastic effects:
In order to reach the level of detection, a given proportion of cells must be irradiated among the population. This constitutes a threshold, which depends on the specified type of cancer and exposure conditions.
3.2 Effects in the embryo and fetus
Comment: The following statement for radiation effects on IQ (lines 1211-1213) is so
reasonable that a similar description is proposed for cancer effects.
However, even in the absence of a true dose-threshold, any effects on IQ following in-utero doses of a few tens of mGy would be undetectable and therefore of no practical significance.
Proposed description for cancer effects:
However, even in the absence of a true dose-threshold, any effects on cancer induction following whole body doses of a few tens of mGy would be undetectable and therefore of no practical significance.
4.4.5 Allowing for the possibility of a low dose threshold for cancer risk
Draft (lines 2170-2171): it (LNT hypothesis) is considered to be a prudent judgment for public policy aimed at avoiding unnecessary risk from exposure.
Draft (lines 2272-2278): In summary the Task Group judges that there is at present no good reason to include the possibility of a low dose threshold in cancer risk calculations for the purposes of radiological protection. On this basis it is recommended that the LNT hypothesis, combined with an uncertain judged value of DDREF for extrapolation from high doses, remains a prudent basis for the practical purposes of radiological protection at low doses and low dose rates.
1. A malignant transformation of a single cell is not synonymous with a tumor or cancer. Tumor formation requires several cell divisions and genome multiplications and the eventual outcome of such iterative processes are fundamentally unpredictable. The contribution of radiation to a malignant cell transformation is not a stochastic effect but a highly conditional one. Cancer induction is such a complex matter that it almost certainly cannot be adequately described by a simple linear model.
2. The ICRP discusses only ga real thresholdh, however, what we need in practical radiation protection is gvirtually safe doseh. Regardless of the debate over whether there are thresholds or not for stochastic effects, the public should be aware that there are practical thresholds for radiation induced adverse health effects.
3. There seems to be no clear evidence of deleterious health effects from radiation exposures at the current dose limits (50 mSv/y for workers and 5 mSv/y for members of the public), which have been adopted worldwide in the second half of the 20th century. Those dose limits can be assumed to have been set below certain gpracticalh thresholds.
4. The large combined study of nearly 96,000 United States, United Kingdom and Canadian nuclear workers showed no excess risk of total cancer mortality excluding leukaemia (ERR= - 0.07/Sv, 90% CI: -0.4, 0.3).
5. The 15 country study published on 29 June 2005 (BMJ online) purportedly suggests that there is a small excess risk of cancer, even at the low doses and dose rates typically received by nuclear workers. However, such a conclusion came from the less reliable analytical results (with very wide confidence interval) on the selected population excluding most of the highly exposed workers because of their potential neutron exposures or internal contamination.
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