Jeder, der für seine (medizinische) Arbeit auf Röntgenbilder angewiesen ist, kennt die Furcht der Patienten vor Röntgenbildern, vor allem wenn es um Bilder bei Kindern geht.
Man muß diese Ängste ernst nehmen und sachlich darauf eingehen. In der Presse kommen immer wieder große Artikel, die auf die Gefahren ionisierender Strahlung hinweisen und durch fast immer unsachliche Berichterstattung diese Furcht schüren.
Immer wieder werden dann Hochrechnungen veröffentlicht, wieviel Krebsfälle durch medizinisches Röntgen verursacht seien (z.B. „Risk of cancer from diagnostic X-rays: estimates for the UK and 14 other countries.“ Berrington de Gonzalez A, Darby S.; Lancet (2004) 31;363(9406):345-51.).
Wenn man sich die Mühe macht, die Arbeiten genau zu lesen, fällt auf, wieviele Annahmen auf dem Weg zum Ergebnis gemacht werden müssen, um dann schlußendlich zu einem kumulierten Risiko von 0,6-0,9% zu kommen). Nun soll das auf keinen Fall bedeuten, mit der Indikationsstellung für Röntgenuntersuchungen leichtfertig umzugehen. Man muß aber eben manchmal auch Fragen stellen, die nicht ‚pc‘ („politically correct“) sind, und dazu gehört die, ob man wirklich das Strahlenrisiko einfach einer schiefen Ebene bis Null runterrechnen kann. Es ist erfrischend, auf eine Zusammenfassung des aktuellen Wissensstandes verweisen zu können, die diese Problematik einmal sozusagen von der anderen Seite her aufrollt.
D.Taverne hat kürzlich ein Buch veröffentlicht (The March of Unreason, Oxford Univ Press), in dem er sich mit derartig tabuisierten Themen auseinandersetzt. Seine Ausführungen zum Strahlungsrisiko sind in der Augustnummer des englischen ‚Prospekt‘ erschienen
Man muß nicht mit all seiner Argumentation zur Kernenergie einverstanden sein, um die Basisargumente des Textes zu akzeptieren.
Prospekt, August 2004
Part of the anti-nuclear case is based on the false, official view that all exposure to radiation is harmful. Small quantities are good for you
Most of us assume that public policy is based on evidence. Alas, not so.
Why do green campaigners, with the notable exception of James Lovelock, reject nuclear power, which emits no greenhouse gases? Because they are frightened of accidents and of radiation emanating from nuclear power stations and nuclear waste. Their fears of radiation are not only widely shared, but they are nourished by official sources and have even become official policy.
Present policies for radiation safety are based on the „linear no-threshold assumption,“ which is endorsed by the International Commission on Radiological Protection. This is the assumption that even the smallest amount of radiation is harmful and may cause cancer and genetic disorders, and that the risk of harm increases proportionately with the dose. On this basis, we should aim to avoid any exposure at all. Accordingly, the standards for radiation protection set by the commission have become more exacting and the maximum exposure dose declared to be safe is continually lowered.
The standard measurement of radiation is set in terms of milliSieverts (mSv) per year. In the 1920s, the maximum dose regarded as safe was 700 mSv. By 1941, it was reduced to 70. By the 1990s, it became 20 for occupationally exposed people and 1 mSv for the general population. Some people believe that the maximum exposure dose should be lower still.
Unfortunately, far from safeguarding our health, current safety standards will almost certainly increase the incidence of cancer. The evidence shows that the effect of radiation on human health is not a linear one, but is aJ-shaped curve. Exposure starts by being beneficial at low doses and only becomes harmful at higher doses. This effect is known as hormesis. A low dose of ionising radiation seems to stimulate DNA repair and the immune system, so providing a measure of protection against cancer. The benefit of low doses of radiation in treating cancer have been known for some time and are confirmed by a mass of evidence, particularly from Japan where it has been studied in detail as a result of Hiroshima and Nagasaki.
Many other examples of the hormesis effect are well known. A bit of sunshine does you good; too much may cause skin cancer. Small doses of aspirin have many beneficial effects; too much will kill you. It also appears to apply to arsenic, cadmium, dioxins and residues of synthetic pesticides, but that is another story.
Epidemiological evidence confirms the hormesis effect of radiation. The prediction that there would be terrible after-effects from the atomic bombs dropped on Hiroshima and Nagasaki on the survivors and their children was proved wrong. Japanese studies of the life expectancy of survivors who suffered relatively low amounts of radiation show that their life expectancy turned out to be higher than those of the control group and no unusual genetic defects have been found in their children. Again, a follow-up study of Japanese fishermen who were contaminated with plutonium after the nuclear tests at Bikini found 25 years later that none of them had died from cancer.
After the Chernobyl disaster it was also predicted that the incidence of cancer among those affected by fallout would greatly increase and there would be huge genetic damage to future generations. It was about as bad an accident to a nuclear power station (a badly constructed one) as is likely to happen. Its psychological effect was huge and changed people’s perception of the risk of nuclear energy all over the world. Indeed, it is constantly cited as an example of the unparalleled threat to health from nuclear disasters.
Tragically, it led to 31 deaths, mainly among rescue workers who were exposed to very high doses of radiation. Yet in the areas around Chernobyl the extra radiation to which people were exposed in the nine years following the accident was slight – an increase of about 0.8-1.4 mSv. In May 2001, in the Ukrainian town of Pripyat, which is now a ghost town after its complete evacuation, the average amount of persistent radiation found was 0.9 mSv a year, five times lower than the level in New York’s Grand Central station. In parts of southwest France the levels of natural radiation are as high as 870 mSv a year.
There is strong evidence that people exposed to low doses of radiation – amounts 100 times more than the minimum recommended – actually benefit. The incidence of thyroid cancers among children under 15 exposed to fallout from Chernobyl was far lower than the normal incidence of thyroid cancer among Finnish children. The death rate from leukemia of nuclear industry workers in Canada is 68 per cent lower than average.
Workers in nuclear shipyards and other nuclear establishments in the US and many other countries have substantially lower death rates from all cancers and are much less likely to die from leukemia. This might be explained by the fact that their health is regularly checked and that only healthy workers are employed. But it corresponds with a mass of other evidence that people who live in areas of unusually high natural radiation, in Japan, China, India and the US, are less likely to die from cancer than a control group.
These facts destroy what are perhaps the strongest objections to nuclear power. They show that the regulations seeking to enforce present, let alone proposed, minimum standards of safety not only cost billions of pounds and have undermined the prospects of our development of nuclear power, but do more harm than good. It is time that we looked more closely at the phenomenon of hormesis and in particular at the successful Japanese experience of using low-dose radiation in the treatment of cancer patients. When the evidence is clear, we should not allow it to be brushed aside by conventional wisdom and ignorance.
Dick Taverne’s book „The March of Unreason“ will be published in November by Oxford University Press