| Statement by the Academy of Medicine of France, December 4, 2001 source | |
Medical Irradiation, Radioactivity Releases, and Disinformation: The Academy of Medicine, preoccupied by the problems that arose in the public about medical exposure to X rays and radioactive releases in the environment, and erroneous information that these subjects give rise to, wishes to give an opinion on this subject.An opinion by the Academy of Medicine Humanity is exposed to ionizing radiation Since the beginning, life developed in a bath of ionizing radiation to which it is adapted. These radiations have a cosmic origin or originate in the earthly crust where, since the creation of the earth, the unstable isotopes of the elements of very long physical half-lives remain: thorium, uranium, potassium, and rubidium. Natural exposure results therefore from internal and external sources, both characterized by various physical properties and different effects on human body. The presence of radionuclides in the environment results in an average radioactivity of 10,000 Bq in the human body, essentially from carbon-14 and from potassium-40 whose concentration is regulated by homeostatic control of intracellular potassium content. Average exposure of humans to natural sources is evaluated to 2.4 mSv per year expressed as effective dose. It exists nevertheless with important variations according to the altitude and nature of the rock and soils in the ground, generally varying from 1 to 10 mSv, and attaining more than 100 mSv in wide regions such as Kerala in India, or the city of Ramsar in Iran (1). These natural variations involve different target tissues for the dose being delivered, such as lung for radon, kidney for uranium, bones for radium, and bones, hepatic and systemic phagocytes for thorium, of which the behavior and the radiological characteristics are similar to those of plutonium. To natural background irradiation is added, since the end of the 19th century, a diagnostic medical irradiation which delivers an average of about 1 mSv per year, but with variations from less than 1 mSv to more than 20 mSv per year. And last, since 1950, it is necessary to add irradiations of industrial origin - notably the one from producing electricity by nuclear energy (extraction and treatment of uranium, functioning of reactors, etc.) corresponding to an exposure of the order 0.01 to 0.02 mSv per year - and one of the other natural sources, from coal extraction and burning to 0.01 mSv per year. In addition, radioactivity releases to the atmosphere contribute to an average exposure of 0.005 mSv/yr, and the Tchernobyl accident to about 0.002 mSv/yr (1). In measuring dose effectiveness, the biological effects of the different types of ionizing radiation are identical whether their origin is natural or artificial. Exposure of workers to ionizing radiation (200,000 in France, of which more of than half are in the medical sector) results, in France, in an average exposure of 2 mSv per year (OPRI annual report) with less then 1% surpassing the average statutory limit of 20 mSv per year. Except for diagnostic irradiations, these exposures are characterized by low dose rate, chronic irradiation doses. This aspect distinguishes them clearly from accidental and therapeutic irradiations that are performed at high dose-rate, causing instantaneous accumulation of damaged molecules that perturb components of cellular repair mechanisms, with as little as a few absorbed mGy in a few minutes (2). Dismantling of nuclear power plants and nuclear waste storage are activities that make small dose increases to the populations at very low dose rates (about 0.005 µSv per year for iodine-129 for example) (1), essentially by transfer in the food chain of various man-made radionuclides of long half-lives leading to either: –homogenous exposure of the whole body (as in the case of natural potassium-40), or to –selective organ exposure, e.g., to the large intestine, bone, liver and kidney, as in the case of the natural isotopes of uranium and thorium. It is therefore legitimate to infer their possible effects on human health from those known to result from natural sources which expose populations of many millions of residents. The health consequences of the exposure of humans to a few mSv. There exists data (3) establishing that high natural exposure is associated in adults to an increased rate of chromosome aberrations of the circulating lymphocytes, a biological indicator of exposure. It cannot be concluded, however, that this is an index of harm since there are detected no global increase of cancer risk (4), increase of congenital malformations (5), or abnormalities induced by cytogenetic effects with newborns (6), in the well-studied population of the particular highly-exposed region of Kerala India to external irradiation and to internal contamination. Identical conclusions are obtained in the exposed Chinese populations (7-8). And last, as stated by the NCRP in the United States (9): «It is important to notice that the incidence of cancers in most of the exposed populations to low-dose radiation has not been found to be increased, and that in most of the cases this incidence seems to have been reduced». | |
| The hypothesis of the risks of cancer induced by low doses and dose-rates is founded on the extrapolation of data of highly-exposed human groups, applying the risk as being constantly proportional to the received dose without being limited by a threshold, the linear no-threshold (LNT) assumption. This hypothesis conflicts with itself and has many scientific objections (10); and it is contradicted by experimental data (11) and epidemiology. In the groups having received more than 200 mSv as adults, and 100 mSv as infants, excesses of cancer have been observed: in e.g., Japanese atomic bomb survivors in Hiroshima and Nagasaki, irradiated medical patients, nuclear workers, and residents of the former-USSR contaminated by nuclear wastes. No excess of cancers has been observed for doses lower than 100 mSv. A doubt remains nevertheless in the case of irradiation for x-ray in utero from 10 mSv because the epidemiological data are contradictory (12). Having not observed excess cancer does not allow an effect for low doses to be excluded because of statistical limitations. Nevertheless it is necessary to recall that the linear theory with no threshold (LNT): -is contradicted by the observation of thresholds for bone cancers induced by radium-226, and cancers of the liver induced by Thorotrast; -is not compatible with induced leukemias in Hiroshima, nor with the patients treated by radioactive iodine (1,10,13). Besides, the historic epidemiological study of the British radiologists for the period 1897-1997 (14) showed that for the registered radiologists after 1954 these practitioners have no excess of cancers in comparison with their non-radiologist colleagues, with a tendency to a lower cancer rate, as in the case of populations described by the NCRP (9). Similar deficits were observed for many groups of exposed professional workers to ionizing radiation, notably radiologic technicians: while the frequency of cancers increased in their jobs during the period when there was limited radiation protection, the excesses of cancers disappeared when regulatory limits were reduced to 50 mSv/yr, as enforceable up to 1990 (12). These observations, associated with the recent biological data, showing complexity and the variety of molecular and cellular mechanisms that control cell survival and mutagenesis according to the dose and dose-rate (1,2,11,13), remove all scientific rationale to a linear extrapolation that overestimates very widely the effects of low doses and dose-rates. One cannot add the exposures of a few mSv/yr, and a fortiori lower than 0.02 mSv/yr, delivered to a large number of individuals (as done with the use of collective doses) to estimate the risk of excess cancers (15). The Academy of Medicine, joining the position of the large international institutions, strongly affirms that such calculations have no scientific validity, notably to evaluate the associated risks to radiation, such as the effects claimed outside the former-USSR from the fallout from Tchernobyl. The UNSCEAR 2000 report and the controversy with the OCHA. The Tchernobyl catastrophe has caused to this day about 2,000 cancers of the thyroid in children, essentially from exposure to iodine-131 and the short-lived iodine isotopes. The delivered doses to the thyroid were on average of the order of 1 Gy, and of 3 Gy on average in the most exposed regions (16). This carcinogenic effect is therefore in keeping with the sum total of our knowledge of radiation risks. In 2000, UNSCEAR concluded that there is an absence of excess leukemias and of cancer other than thyroid cancer in the population around Tchernobyl. It also did not find a relationship between the exposures to radiation and congenital malformations in these populations (1). This conclusion was questioned in 2001 by the OCHA, the humanitarian organization of the UN, but the OCHA publication was refuted in a response by the UNSCEAR committee, which alone has the medical and scientific competence to speak with the name the UN and of the WHO on this subject (17). A conference was therefore held in Kiev in June 2001, with the WHO, OCHA, UNSCEAR, ICRP and IAEA, and the conclusions have been published (annex). These conclusions find that the health conditions are alarming because of the general deterioration of the health and social conditions, notably in Belarus, but do not contradict the UNSCEAR conclusions. In fact, this deterioration is probably caused by the living conditions of the relocated populations, associated with psycho-sociological factors. Different questions have been raised that do appear to necessitate epidemiological research of the conditions of the catastrophe consisting of multiple susceptible factors that altered the health of populations: this is the recommendation of the Kiev conference. It is possible to reduce human exposure to ionizing radiation, in particular of radiation medical origin, with the necessary means. Radiological examinations represent, by very far, the principal cause of irradiation of human origin (effective average dose of about 1 mSv/yr in France). The recent direction of the European Union introduces two notions to this subject: -cost-optimization (to reduce as much as possible the dose per examination), -and justification (to evaluate the benefit and the risk of each examination, and to not practice it unless it is advantageous). These principles necessitate therefore the evaluation of effective doses received by the examined subject and the relevant risks. Now, according to the examinations and the techniques used, the effective doses vary from a fraction of a mSv to several tens of mSv (examinations by x-ray scanners or radiological interventions) and the risks vary widely according to age. An over-evaluation of risks could deprive a child of a useful examination; inversely, an under-evaluation could favor the multiplication of medical X ray examinations that are not useful. The Academy counsels therefore, in a first step: 1) to focus on the study and evaluation of examinations from which the potential risks are the largest: x-ray scans with young subjects, multiple radiological examinations with premature interventional angiography; 2) to promote the likely techniques to reduce or to eliminate irradiation without harm to the quality of clinical information and to stimulate the technical and basic research in this area; 3) to conduct epidemiological studies on groups of patients, notably infants, which have received the most important doses from radiological examinations; and 4) to favor the initial and continuing training of clinicians in matters of radiation protection. It is unacceptable, while irradiation of medical origin represents, in France, 95% of the irradiation added to the natural background, that there is little benefit to affect reduction in the industrial environment by applying radiation protection at very high costs. It is necessary to define health priorities in the matter of releases. Outside of this context, some recommendations can be undertaken concerning the problem of radiation releases in the matter of health. It appears essential to support epidemiological studies concerning the populations exposed naturally to high-level background radiation, and even concerning the populations of the ex-USSR that were massively exposed to radioactivity releases and to other pollution. In the framework of studies dealing with potential health effects of nuclear waste management, the priority isotopes should not be selected according to the collective dose that some would use, but according to the potential doses to individuals because the calculated collective doses from low individual doses to a few microSieverts cannot have any effect on health. A significant national effort should be undertaken, as the one undertaken in the framework of the programs of the U.S. DOE, on the biological mechanisms in the cellular response to doses below 100 mSv, in particular, health effects from DNA repair, cell signaling, and the hereditary transmission in DNA sequence encoding of parental DNA modified by irradiation. | |
| – Recommendations – The Academy of Medicine:1 – recommends increased effort for radiation protection in the area of radiological examinations, on the one hand to reduce received doses from certain types of examinations (x-ray scans with infants, interventional angiography, lung X ray examinations with premature treatments, etc…), and on the other hand, to allow radiology services, notably in radio-pediatrics, to obtain benefits of well-educated physicists for dosimetry and quality control of the devices, in a way similar to that previously undertaken with mammography in breast cancer surveys. It recommends to this end to support clinical and technical research in this area. 2 – recommends an effort of basic research: on the biological mechanisms activated by the repair of DNA damage after low doses up to 100 mSv; and on the effects of these doses on the exchanges of intra- and inter-cellular molecular signals. 3 – denounces utilization of the linear no-threshold (LNT) relation to estimate the effect of low doses to a few mSv (of the order of magnitude of variations of natural radiation in France) and a fortiori of doses hundreds of times lower, such as those caused by radioactive releases, or 20 times lower, such as those resulting in France from the fallout of radioactive materials from the Tchernobyl accident. It associates with many international institutions to denounce improper utilization of the concept of the collective dose to this end. These procedures are without any scientific validity, even if they appear be convenient to administrative ends. 4 – subscribes to the conclusions of the 2000 Report of the Scientific Committee on the Effects of Atomic Radiation of the United Nations (UNSCEAR) concerning the analysis of health consequences of the Tchernobyl accident, and denounces the propagation of allegations concerning excesses of other cancers than the thyroid cancer, and excesses of congenital malformations. 5 – recommends introduction of the ADIR (Annual Dose of Incorporated Radioactivity, being equivalent to 0.2 mSv, resulting from homogeneous exposure of the human body to natural potassium-40 and carbon-14) as this dose equivalent is almost constant whatever the size of the individual and the geographic region. 6 – The Academy of Medicine, in accordance with its October 3rd 2000 statement, continues to recommended maintaining without modification the European directive concerning regulatory limits (to 100 mSv/5yr). To substitute dose limits of 20 mSv/yr would reduce the flexibility of the European norm, all without any health advantage, and would harm the functioning of medical radiology services while making the improvement of applicable techniques more difficult. Glossary -Bq or becquerel, the radioactivity characterized by a disintegration per second. In the human body 10,000 Bq of the natural sources represent 1 ADRI that is equivalent by convention to a dose equivalent of 0.2 mSv -Gy or gray, the absorbed dose corresponding to 1 joule per kg. -Sv or sievert, the unit of equivalent dose obtained from the product of the dose absorbed by the weighting factor for radiation quality (1 for X, beta and gamma radiations … 20 for alpha radiation). The effective dose, also expressed in Sv, is the product of the dose equivalent by the weighting factor for organs (0.05 for the thyroid… 1 for the entire body). IAEA: International Atomic Energy Agency ADRI: Annual Dose of Incorporated Radioactivity, recommendation G. Charpak. DOE: Department of Energy, U.S. ICRP: International Commission on Radiation Protection NCRP: National Council on Radiation Protection and Measurements (USA) OCHA: Office for the Co-ordination of Humanitarian Affairs WHO: World Health Organization UNSCEAR: United Nations Scientific Committee on the Effects of Atomic Radiation References:
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