Radiation from radioactive decay causes the material it passes through to become ionised, hence the term 'ionising radiation'. Ionising radiation attacks the cells of the body by producing chemical changes in the cell DNA, leading to abnormal cell growth.
The effect on body tissues depend on:
- the type of radiation
- the dose and duration of exposure
- whether the source is internal or external to the body.
Ionising radiation is commonly encountered in healthcare through:
- X-rays
- radioactive materials used as tracers to help diagnose diseases
- radiotherapy
- occasionally treating people who have been exposed to excessive amounts of radiation, either deliberately or through an accident.
The use of these procedures in healthcare has to be justified by the benefit of the patient - exposure to a small amount of radiation may carry a tiny risk for health, but this may be outweighed by the benefits of diagnosing and then being able to treat serious conditions.
However, these procedures may expose others to small doses of radiation - generally those who carry out the procedure or who are caring for the patient. Because there is no benefit to these people, exposure is strictly controlled and has to be kept below certain limits.
There are strict regulations on the permitted radiation exposure for employees, although the emphasis should be on reducing the exposure as much as possible, not just keeping within legal limits.
Sources of ionising radiation
Healthcare is one of the main workplaces where ionising radiation is deliberately used - others examples include the nuclear industry, academic research centres and the construction industry (where X-rays are used for non-destructive testing). Smoke detectors, used in many workplaces and homes, also use low levels of ionising radiation.
Ionising radiations can also occur naturally, the best example of this being radon, which is a radioactive gas that occurs mainly at or near granite outcrops where there is a presence of uranium. It is particularly prevalent in Devon and Cornwall. The gas normally enters buildings from the substructure through cracks in flooring or around service inlets. Buildings where radon is detected may need to be fitted with sumps and extraction fans.
We are all exposed to a little radiation in the environment, but at levels which are not considered harmful. This is referred to as background radiation.
When radiation is used in healthcare, staff may be exposed to a small dose during the procedure or while they are caring for a patient who has received treatment with radioactive substances.
The legal position
The Ionising Radiation Regulations 1999 lay down very strict rules about how
radiation may be used and the limits of exposure for staff, including young staff and pregnant women.
These include:
- restriction of employees' exposure
- control of access to areas where radiations may be present
- appointment of suitably trained or qualified persons to ensure safe use of sources
- implementation of rules for the safe use of sources
- training and instructing any employee who uses radiation sources
- measuring the exposure levels of employees working with radiations
- provision of medical examinations for staff exposed to sources
- keeping accurate records of the use and locations of all sources
- reporting to the Health and Safety Executive (HSE) any damage to or loss of a
source
- investigating cases of over-exposure and taking corrective action.
Guidance on these regulations is given in HSE publications L121, Work with ionising radiation. Where the use of radiation sources is contemplated, advice should be sought from the supplier, the National Radiation Protection Board and/or a suitably qualified consultant.
The limits on effective dose (dose to the whole body) introduced by the IRR99 are for employees aged 18 years or over, 20 millisieverts in a calendar year (except that in special cases employers may apply a dose limit of 100 millisieverts in five years with no more than 50 millisieverts in a single year, subject to strict conditions). In comparison, a single chest X-ray would expose a patient to 0.02 millisieverts.
There is a lower limit for trainees of six millisieverts in a calendar year; and one millisievert in a calendar year for any other person, including members of the public
and employees under 18, who cannot be classed as trainees.
Limits for pregnant women are lower than this.
