Radiation Exposed Populations

Introduction

Researchers from all over the world are investigating the health consequences of exposure to ionising radiation. They are seeking answers to questions which range from how to improve the benefits of using radiation to treat diseases such as cancer through to what the potential adverse health effects of exposure may be. As part of this endeavour, many scientists are studying the effects of exposure within different groups of people who are known to have been exposed to radiation. In this article we briefly describe these populations, as the findings from these studies are often very relevant for British nuclear test veterans and their families.

The main human populations include:

People who receive natural doses of radiation that are higher than the global average dose of 2.4 mSv per year.
Patients who receive doses of radiation for medical reasons.
Workers who are exposed to radiation because of their occupation.
People who are exposed to radiation through war.
People who are exposed to radiation through accidents.

High Natural Background Radiation

We all receive a natural background radiation dose which depends upon our geographical location. The annual natural dose for the average person in the UK is 2.3 mSv. However, this is higher in places where the rocks in the ground contain higher levels of uranium (a radioactive substance), for example in Cornwall the annual radiation dose is 7.8 mSv which is more than three times the UK average.

The radioactive substances in the ground, uranium and thorium, produce radon gas, which is the most hazardous part of this background radiation. This radioactive gas emits alpha-particles, which can damage lungs and other cells when it is inhaled. Indeed, radon is the second most important cause of lung cancer after smoking, though smoking poses far greater health risks. Scientists have found that the combination of exposure to radon gas and smoking (which is predominately a chemical hazard) is more harmful than either radon or smoking alone.

Medical Exposure to Radiation

Many of us will have been exposed to radiation such as X-rays for medical reasons, which can range from the lower doses which are used for diagnostic purposes to the high doses which are given during radiotherapy.

The average annual radiation dose for medical purposes in the UK is 0.44 mSv, which is much lower than for the United States (3 mSv). The bulk of the UK medical average dose (0.40 mSv) is accounted for in diagnostic procedures. Many procedures that we commonly receive such as dental X-rays (0.005 mSv) and chest X-rays (0.014 mSv) have very small doses. There are some diagnostic procedures which have larger doses. For example, a computerised tomography (CT) scan has a dose in the region of 10 mSv. Doctors get useful information from these procedures, which are performed based on medical need and the benefits gained for the patient.

Many procedures that we commonly receive such as dental X-rays (0.005 mSv) and chest X-rays (0.014 mSv) have very small doses.

Radiotherapy patients receive the highest doses of radiation because of the medical need to kill cancer cells. The total dose applied depends upon the type of cancer being treated and the stage of its progression. For example, a dose in the region of 20 to 80 Gy may be required to treat a solid tumour. This could be fatal to the patient if applied as a single dose, so the radiation is applied in repeated doses called fractions with each single dose being no more than 2 Gy.

Targeted radiotherapy is a newer form of radiotherapy which ‘concentrates’ or targets a radioactive substance at specific disease sites to kill the cancer cells whilst minimising damage of non-diseased normal tissue. One example of this treatment is where patients are injected with radium (an alpha-particle emitter) to treat late-stage prostate cancer which has spread to the bone.

Occupational Exposure to Radiation

Workers performing their normal, day-to-day duties receive low radiation doses in a number of occupations. For many of these professions exposure levels are monitored, any health effects are recorded and exposure limits are set using all of the available evidence. In the UK, the annual whole body dose limit for a worker is currently set at 20 mSv, based on research into health effects. In practice, most workers do not reach these limits.

Three out of four workers are exposed to ionising radiation work in the healthcare sector with an annual average radiation dose per worker of 0.5 mSv. This includes members of clinical teams who use radiation during surgery or to treat cancer.

Workers in the nuclear power industry have been monitored for exposure for several decades. The global average annual dose for these workers has fallen from 4.4 mSv in the 1970s to 1 mSv today, because of the successful implementation of radiation protection measures. This is lower than the doses experienced by coal miners (2.4 mSv). Coal miners may not consider themselves to be radiation workers, however, they are exposed to radioactive radon gas.

A very large health effects project called "The Million Persons Study" is in progress in the USA. This study includes registered radiation workers in a range of occupations and also a population of American nuclear test veterans.

Atomic Bombings of Japan

A joint Japanese-American scientific body called the Radiation Effects Research Foundation (RERF) is investigating the long-term health consequences of the survivors and their descendants of the atomic bombings of Hiroshima and Nagasaki in 1945. Scientists from RERF (formerly known as the Atomic Bomb Casualty Commission) have produced thousands of peer-reviewed scientific papers and continue to publish findings today.

RERF’s investigation into the health of the survivors is called the Life Span Study (LSS), because starting from 1950 all of the participants are subject to follow-up studies at regular intervals for the rest of their lives. The areas of health that have been monitored by RERF include cancer, non-cancer diseases (such as cataracts and heart disease) and mortality.

To date, RERF have found that people who were exposed to radiation have a greater risk (called an excess relative risk) of getting cancer during their lifetime than people who had not been exposed.

The size of this excess relative risk was found to depend upon the radiation dose. It was found that the excess relative risk could be as high as 50% for people who received a dose of 1 Gy. However, just 2.5% of the survivors received this dose or more. Approximately, 80% of survivors received a dose of 100 mGy or less and their excess relative health risks are considered to be very low. There are uncertainties in precisely quantifying the low risks to health for low radiation doses (below 100 mGy or 100 mSv) and for low dose rates (below 0.1 mGy/minute) and a great deal of research is underway to address this.

There is evidence that people who were either young children or who were in the womb at the time of the bombings do have a greater lifetime risk of developing cancer than people exposed as adults. Furthermore, some children exposed to radiation when in the womb were born with smaller head sizes and mental disabilities.

RERF’s investigation into the children of the survivors conceived after the bombings is called the F1 study, because they are following the health of the first generation of the survivors’ descendants over their entire lifetimes. Scientists have found no clear evidence of an increase in the incidence of cancer or of any other health condition in children conceived after the time of the atomic bombings.

Scientists have found no clear evidence of an increase in the incidence of cancer or of any other health condition in children conceived after the time of the atomic bombings.

Radiation Exposure through Accidents

The most serious accident in the history of nuclear power occurred at the Chernobyl nuclear power plant on 26th April 1986. The Chernobyl accident resulted in the exposure of different populations to varying low to high doses of radiation which were received over relatively short times or over a period of several years.
populations to varying low to high doses of radiation which were received over relatively short times or over a period of several years.

Plant workers and emergency workers, especially firefighters, received large radiation doses at the scene of the accident. This caused a number of cases of radiation sickness requiring hospitalisation (134) with some cases leading to death (28 died within three months of the accident).

Those surviving plant workers, emergency workers and the recovery workers who were tasked with decontaminating the scene of the accident (called the liquidators) have been enrolled in health surveillance programmes. This will allow individuals to be supported and also help scientists to understand the long-term health effects such as cancer which may emerge decades after the accident.

The accident resulted in a large quantity of radioactive material being released into the environment. The contamination of fresh milk with the short-lived radioactive substance, iodine-131 (half-life 8 days) led to children and adolescents receiving large doses of radiation to their thyroid glands. This has led to an excess of cases of thyroid cancer. However, there has been no relative increase in thyroid cancer amongst people who were adults at the time of the accident.

Many residents of contaminated areas in Belarus, the Russian Federation and the Ukraine were evacuated from their homes. Many of these residents would have received low doses of radiation and although there are many uncertainties about health consequences after low dose exposure, the risks are considered to be small.

However, many evacuated residents showed symptoms of psychological stress. Indeed, more people were affected by the Chernobyl accident with regards to their mental health than their physical health.