Medical irradiation, radioactive waste, and disinformation:
The position of the French Academy of Medicine
27 November 2001
The French Academy of Medicine, preoccupied by the concerns that arose in the public regarding medical exposure to X rays and radioactive waste in the environment, and by erroneous information that these topics give rise to, wishes to express its position.
Humanity is exposed to ionizing radiation
From the beginning, life developed in a bath of ionizing radiation to which it has adapted. This radiation has a cosmic origin or originates in the earth’s 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 the 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 potassium-40 whose concentration is regulated by homeostatic control of intracellular potassium content. Humans are exposed to natural sources of ionizing radiation and the effective dose they receive is on the average equal to 2,4 mSv per year. This dose varies according to the altitude and nature of the soil, from 1 to 10 mSv, and attains 100 mSv in large regions such as the Kerala in India, or the city of Ramsar in Iran (1). Various tissues are specifically irradiated, such as the lung by radon, the kidney by uranium, bones by radium, and bones, hepatic and reticulo-endothelial system by thorium whose metabolic and radiological characteristics are similar to those of plutonium. The dose the tissues receive varies widely throughout the world.
Since the end of the 19th century, to natural irradiation has been added diagnostic medical irradiation delivering an average of 1 mSv per year, but with variations going from less than 1 mSv to more than 20 mSv per year.
Since 1950, it is necessary to add irradiation of industrial origin - notably that of nuclear energy for the production of electricity (extraction and treatment of uranium, functioning of reactors) corresponding to an exposure of about 0.01 to 0.02 mSv per year. Coal, a natural source, represents 0.01 mSv per year. Nuclear testing in the atmosphere contributes to an average exposure of 0.005 mSv/yr and the Chernobyl accident to 0.002 mSv/yr (1).
For equal doses, 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 than half is 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. With the exception of diagnostic irradiation, these exposures are characterized by a low dose rate, close to types of chronic irradiation. The dose rate clearly distinguishes them from accidental and therapeutic irradiations which have a high dose-rate, leading to an instantaneous accumulation of damaged molecules that perturb the cell repair mechanism components, from a few mGy absorbed in a few minutes (2).
The dismantling of nuclear power plants and nuclear waste storage facilities are activities that contribute to small increases of delivered doses to the population at very low dose rates (1) (about 0.005 µSv (1) per year for iodine-129 for example). This is due essentially to the transfer to the food chain of various man-made radionuclides of very long half lives leading to — either homogenous exposure of the entire body, (as in the case of the potassium natural 40), or to selective organ exposure, especially to the digestive tract, 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 several millions.
The health consequences of the exposure of humans to some 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 it is an index of harm since no global increase of cancer risk (4), or increase of congenital malformations (5), or abnormalities in newborns induced by cytogenetic effects (6) were detected in the well studied population of Kerala region, which is highly exposed to external irradiation and to contamination. Identical conclusions are obtained in the exposed Chinese populations (7-8). As the NCRP reported in the United States (9) : "It is important to note that the rates of cancer in most of the exposed populations to low level radiation have not been found detectably increased and that, in most cases, the rates have appeared to be decreased. "
The hypothesis of the risks of cancer induced by low doses and dose rates is founded on the extrapolation from data of highly exposed human groups, postulating that the global risk is constantly proportional to the received dose without being limited by a threshold (LNT). This hypothesis raises many scientific objections (10) and is contradicted by the experimental data (11) and epidemiology.
In the groups having received more than 200 mSv in adults and 100 mSv in children, an increase in cancer incidence has been observed: the survivors of Hiroshima and Nagasaki, irradiated patients, nuclear workers, and residents of the former USSR contaminated by nuclear waste. No cancer excess was observed for doses lower than 100 mSv; a doubt remains nevertheless in the case of irradiation by X-ray in utero from 10 mSv as the epidemiological data are contradictory (12).
Even though no excess of cancer has been observed, effects from low doses cannot be excluded because of statistical limitations. Nevertheless, it is necessary to recall that the linear theory with no threshold is contradicted by the observation of thresholds for bone cancers induced by radium-226 and cancers of the liver induced by Thorotrast. It is also not compatible with induced leukemias in A-bomb survivors and with patients treated by radioactive iodine (1,10,13). Furthermore, the epidemiological study of British radiologists for the period 1897-1997 (14) showed that after 1954 there is no excess of cancers in these practitioners in comparison with their non-radiologist colleagues. On the contrary, the incidence tended to be lower, as in the case of populations described by the NCRP (9). Similar findings were observed for many groups of exposed professional workers to ionizing radiation, notably the radiological technicians (12). While the frequency of cancers was increased during the period when no radioactive protection measures were taken, the excess of cancers disappeared when regulatory limits were reduced to 50 mSv/year, as enforced up to 1990 (12).
These observations, as well as recent biological data, show the complexity and the variety of molecular and cellular mechanisms governing cell survival and mutagenesis according to the dose and dose rate (1,2,11,13), remove all scientific rationale for a linear extrapolation that very greatly overestimates the effects of low doses and low dose rates. Exposures of a few mSv/yr cannot be accumulated, especially for those 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 other large international institutions, strongly states that such calculations have no scientific validity, notably to evaluate the risks associated with low dose or dose rate radiation such as in the case of the fallout from Chernobyl outside the USSR.
The UNSCEAR 2000 report and the controversy with the OCHA
The Chernobyl catastrophe has caused to this day about 2,000 cancers of the thyroid in children, essentially by exposure to iodine-131 and to the short-lived iodine isotopes. The delivered doses to the thyroid were in the order of 1 Gy and 3 Gy on average in the most exposed regions (16). This carcinogenic effect is therefore in keeping with our current knowledge. No increase in thyroid cancers was observed outside of the USSR, for example in Poland or other bordering countries.
In 2000 UNSCEAR concluded that there is an absence of excess in leukemia and in cancers other than thyroid cancer in the population around Chernobyl; it 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, that alone has the medical and scientific competence to speak in the name the UN and WHO on this subject (17). A conference was therefore held in Kiev in June 2001 with WHO, OCHA, UNSCEAR, ICRP and the IAEA, and the conclusions have been published (17). These conclusions find that health conditions are alarming because of the general deterioration of 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, as well as psycho-sociological factors. Different questions have been raised that do appear to necessitate research on the epidemiology of the conditions of the catastrophe consisting of multiple possible factors that altered the health of these populations: this is the recommendation of the Kiev conference.
It is possible to reduce human exposure to ionizing radiation, in particular of medical origin, but this necessitates means.
Radiological examinations represent, by far, the principal cause of irradiation of human origin (effective dose about 1 mSv/yr in France). The recent directive of the European Union introduces two important notions to this problem: 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 useful). These principles necessitate therefore the evaluation of effective doses received by the patient examined and the associated risks. According to the examinations and the techniques used, the effective doses vary from a fraction of a mSv to several tens of mSv (examination by CT scan or interventional radiology) 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: 1) to focus on the study and evaluation of examinations from which the potential risks are the largest: CT scans of young subjects, multiple radiological examinations of premature infants, and interventional radiology, 2) to promote techniques likely to reduce or to eliminate irradiation without harming the quality of clinical information and to encourage technical and fundamental research in this area, 3) to conduct epidemiological studies on groups of patients, notably children, having received the highest doses from radiological examinations, 4) to favor initial and continuing training of clinicians in matters of radiation protection.
It is unacceptable that, while irradiation of medical origin represents in France 95% of irradiation added to natural background irradiation, so little money is devoted to its reduction, whereas radiation protection in industry is well funded.
It is necessary to define health priorities with regard to radioactive waste.
Outside of this context some recommendations can be made concerning the problem of radioactive waste and health. It appears essential to support epidemiological efforts concerning the populations exposed naturally to a high level of radiation, as well as populations of the ex-Soviet Union massively exposed to radioactive waste and other pollution. In the framework of studies dealing with potential health effects of nuclear waste management, the isotopes that should be considered in priority should not be selected according to the collective dose that would result, but according to the individual dose potentials, since the calculated collective doses from low individual doses to a few microSieverts do not have any health significance. An important national effort should be undertaken, as was done within the framework of the programs of the U.S. DOE, on the biological mechanisms involved in the cellular response to doses below 100 mSv, in particular regarding effects on DNA repair, cell signaling, and the hereditary transmission in DNA sequence encoding of parental DNA modified by irradiation.
The French Academy of Medicine:
1 — recommends increasing efforts in radiation protection in the area of radiological examinations, on the one hand to reduce received doses from certain types of examinations (CT scans of children, interventional radiology, lung X-ray examinations of premature infants, etc…) and on the other hand, to allow radiology departments, notably in radio-pediatrics, to benefit from a staff well trained in dosimetry and capable of ensuring the quality control of equipment, in a way similar to that previously done with mammography in breast cancer screening. It also recommends reducing patient exposure through increased clinical and technical research in this area and improved training.
2 — recommends an effort in fundamental research: on the biological mechanisms activated by the repair of the 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 the utilization of the linear no-threshold (LNT) relation to estimate the effect of doses lower than a few mSv (equivalent to variations of natural radiation in France) and of doses hundreds of times lower, such those caused by radioactive waste, or 20 times lower, such as those resulting in France from radioactive fallout from the Chernobyl accident. In agreement with many international institutions, the Academy denounces the improper use of the concept of the collective dose to this end, since these procedures are without any scientific validity, even if they appear to be convenient for administrative purposes.
4 — subscribes to the conclusions of the 2000 Report of the Scientific Committee of the United Nations (UNSCEAR) concerning the analysis of health consequences of the Chernobyl accident, and denounces the propagation of allegations purporting an excess in cancers other than that of the thyroid, and an excess of congenital malformations.
5 — recommends the 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 statement given October 3rd 2000, continues to recommend 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, without offering any health advantage, and would harm medical radiology departments by making the development of new 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 Agency of Atomic Energy
ADRI: Annual Dose of Incorporated Radioactivity, recommendation G. Charpak.
DOE: Department of Energy, US
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