Radiation risk
As radiation risk is defined as the probability of a specific population, the ionizing or other high-energy radiation was exposed to the consequences of this additional radiation exposure ill or dies. So it is not about acute radiation sickness , but about stochastic consequences of exposure to relatively low radiation doses . Often this radiation damage refers to cancer as a secondary disease.
The International Commission on Radiation Protection (ICRP) specifies the following formula for calculating the risk factor (for persons who are not professionally exposed to radiation):
- If 100 people are exposed to an additional equivalent dose of 1 Sievert , radiation-induced cancer can be expected in five cases; four of these cancer cases are fatal. This relationship applies per Sievert, ie with an equivalent dose of 2 Sievert, the cancer risk is increased by 10 percentage points, etc. This is chronic exposure over several decades, not acute exposure, for example through an accident.
In the case of cancer, it cannot be determined whether they were caused by chemical influences, viruses or radiation, or whether they occurred spontaneously. Such DNA changes that can be caused by exposure to radiation can also occur "spontaneously". Therefore, in a single person, a causal relationship between radiation exposure and clinically manifest cancer cannot be proven in principle. A significant risk statement is only ever possible for a large collective, and only if other causes for an increase in the cancer rate could be ruled out.
Determination of the radiation risk
The knowledge about the effects of high-energy or ionizing radiation comes from the epidemiological observation of patients, victims of accidents, from animal experiments, but also from the investigation of the survivors of the atomic bombs on Hiroshima and Nagasaki .
In the Japanese study ( Life Span Study ) that was further evaluated to date (2009), around 100,000 people affected by the attacks have been recorded since 1950. Attempts were made to reconstruct the dose to which they were exposed during the explosions, for example based on their whereabouts. The cohort size (the number of people recorded) fluctuates depending on the publication, as people were added in the course of the study and a distinction is also made between cities.
The Radiation Effects Research Foundation (RERF) collects the data from the Japanese study, and organizations such as UNSCEAR (United Nations Committee on the Effects of Atomic Radiation) and BEIR (Committee of the Academy of Sciences of the USA) investigate the effects of the Radiation exposure to humans. They determine the course of the mortality rate (death rate) depending on the age of the radiation victims compared to the spontaneous rate and also the dose dependency of the number of additional deaths. The International Commission on Radiation Protection (ICRP) uses this to develop risk models, radiation protection recommendations and guide values for risk coefficients . These are subject to constant change and criticism. Children and other radiation-sensitive people are not explicitly taken into account, which leads to special assumptions for the radiation protection of these groups.
In the following, the effect of radiation is shown first on the risk of mutations with serious consequences and then on the tumor rate.
Radiation effects
Radiation Induced Mutations
A mutation is a change in DNA, be it individual bases , genes or chromosomes . Ionizing rays can cause mutations. It is known from experiments on fruit flies , bacteria , yeast and other microorganisms that the mutation frequency increases proportionally with the dose and that there is a linear dose-effect relationship . Experiments with mice were used to investigate whether this also applies to humans. Since mice have a similar number of genes as humans, a transfer of the results is considered justified.
The experiments were carried out under the name Mega Mouse Project . About 8 million mice were screened for seven different mutations (six in the color of the coat and another in the form of crippled ears). The spontaneous rate of these mutations was determined and then the mice were irradiated.
The result: The additional number of mutations is proportional to the dose or the dose rate during fractionation. The doubling dose is 1 Sv , i.e. every increase in the dose by 1 Sv doubles the number of mutations. The ICRP names the overall probability of severe genetic damage as 1% per Sv. Divided into the generations: 1st generation 0.15% Sv −1 , 2nd generation 0.15% Sv −1 , all other generations together 0.70% Sv −1 .
Radiation-induced tumors
The Japanese study shows the following mortality rate curves for leukemia and solid tumors :
leukemia
If the additional rate of leukemia deaths per year is plotted over time (years after exposure), the rate rises from about 5 years after exposure, reaches a maximum 10 to 15 years after exposure, and then subsides again. This means that the mean latency period for the occurrence of radiation-induced (radiation-induced) leukemia cases in the atomic bomb victims is around 15 years.
Solid tumors
The number of radiation-induced tumors increases about 5 years after exposure and has an exponential course, similar to that of the spontaneous rate. 30 years after radiation there are about 20 additional cancer deaths per year and 10,000 people. Even after 30 or 40 years, the rate continues to rise. The mean value of the latency period is around 40 years.
Models for determining lifetime risk
From the data for the time courses, models can be set up for the development of tumors in the course of life.
Absolute risk model
For leukemia, the ICRP considers an absolute risk model to be appropriate: The number of leukemia deaths in addition to the spontaneous rate is proportional to the dose suffered . For the spontaneous rate, which runs roughly exponentially with age, this means: After exposure, the mortality rate rises, but after a peak falls back to the spontaneous rate 20 years later, as if no irradiation took place.
Relative risk model
In the case of solid tumors, the following should apply: The percentage with which the overall curve for age dependency (ergo the spontaneous rate) is increased is proportional to the dose . After exposure, the incidence of tumor deaths increases, even many years later. The exponential spontaneous rate becomes "steeper" after irradiation and increases more rapidly; an equal number of additional deaths is thus reached at an earlier age. The larger the dose, the more rapidly the mortality rate increases.
Dose dependence and risk coefficient
The number of radiation-induced tumor cases depending on the organ dose can be described by a linear function (the higher the dose, the more cancer cases), although large error limits must be observed. Another problem is that radiation doses only differ statistically from zero from around 200 mSv and thus the question is whether the dose dependency is really linear down to zero without a threshold value . It is unclear whether very small doses have harmful effects or whether a certain threshold dose is required before they occur, because most studies are based on findings from exposure at medium to high doses. Some scientists are even of the opinion that low doses of radiation have positive effects ( hormesis ), but this thesis has not been scientifically supported by methodically correct studies.
If one assumes a linear relationship between dose and mortality, one gets a straight line for leukemia and cancer. At a dose of 2 Sv there are 5 additional cases of leukemia and 20 additional cancer cases per 10,000 people per year. The slope of the straight line in the dose-response relationship corresponds to the risk coefficient , so the risk (with the unit deaths per year) is the coefficient times the dose.
In its currently valid recommendation from 2007, the ICRP estimates the additional individual lifetime cancer mortality risk from ionizing radiation in the case of whole-body exposure with a low single dose at a total of 5% per Sv. So if 100 people are exposed to a dose of 1 Sv, 5 of them will likely die of cancer in their lifetime. The coefficient is the sum of individual organ coefficients (e.g. red bone marrow: 0.5% Sv −1 ; lungs 0.85% Sv −1 ; large intestine 0.85% Sv −1 ; stomach 0.7% Sv −1 ; Breast 0.6% Sv −1 ).
Examples of risk calculation
The risk of dying in Germany from cancer caused by natural radiation sources (see table in the article Radiation exposure ) is calculated as follows:
“Risk” = risk factor R × dose H × number of people = 5 · 10 −2 Sv −1 × 2.1 · 10 −3 Sv × 80 · 10 6 people.
The recommendation of the ICRP from 1990 was used. With this formula one can estimate that around 8,400 cancer deaths per year and thus around 3% of all around 220,000 cancer deaths per year in Germany can be attributed to the average natural background radiation. Of course, it should be noted that the actual mean dose values are far lower, differ from region to region and also depend heavily on the individual lifestyle (e.g. diet, travel). If the risk factor is extrapolated linearly to lower dose values (which is controversial), an increase in radiation exposure of 1 mSv (50% of the natural dose) would result in 5 additional cancer deaths per 100,000 people. But that would only be an increase in general cancer mortality from currently 25% to 25.005%. Such increases are epidemiologically undetectable.
The medical contribution to radiation exposure consists of 90% of the use of X-ray diagnostics and 10% of radiation therapy and nuclear medicine. 50% of all X-ray examinations are carried out on patients over 65 years of age who probably do not have to suffer from cancer due to the latency period.
The individual risk should be illustrated by means of an X-ray image of the organ with an organ dose of 0.3 mSv and a total body dose of 0.2 mSv.
- Lung cancer risk = organ dose × organ-related risk coefficient = 0.3 · 10 −3 Sv × 0.85 · 10 −2 Sv −1 = 2.5 · 10 −6 . That's a 1 in 400,000 risk.
- Total cancer risk = effective dose × risk coefficient = 0.2 · 10 −3 Sv × 5 · 10 −2 Sv −1 = 10 −5 . That's a 1 in 100,000 risk.
For comparison: the risk of dying of cancer in Germany (regardless of what caused it) is around 25%. The value fluctuates between 20 and 30% depending on the lifestyle and living space. So to a certain extent everyone takes care of their individual risk; By avoiding long air travel or drugs such as alcohol and cigarettes and choosing your place of residence, it can be reduced accordingly.
Radiation protection
Irrespective of the risk assessments drawn up by committees, it is the task of radiation protection to keep the risk to the population as low as possible. The basic principle is to avoid any unnecessary radiation exposure ( ALARA ). If irradiation cannot be avoided, the dose should be as small and proportionate as possible.
The regulation for unnatural radiation (per person, whole body dose) applies in Germany (according to BfS, 2001): The total population may be exposed to a maximum of 1 mSv per year. Occupationally exposed persons may receive a maximum of 20 mSv per year or 400 mSv per working life. There is no limit value for patients undergoing radiation therapy , but the benefit must always outweigh the risk.
Radiation Fear and Risk Perception
Psychological research has been concerned with the risk perception of radiation since the 1970s . It was found that laypeople do not consistently assess the risks of different types of radiation and that their perception differs significantly from that of experts. Since the 1950s, the term radiophobia has been used to describe a fear of the negative consequences of certain types of radiation.
See also
Individual evidence
- ↑ a b 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. International Commission on Radiation Protection, Oxford, England: Pergamon Press.
- ^ Andreas-Claudius Hoffmann, Kathleen D. Danenberg, Helge Taubert, Peter V. Danenberg and Peter Wuerl: A Three-Gene Signature for Outcome in Soft Tissue Sarcoma. (No longer available online.) Formerly in the original ; accessed on March 13, 2009 . ( Page no longer available , search in web archives )
- ↑ IRCP Publication 103 (2007) , German translation by the BfS
