About Screening
Information Leaflets - Information about the radiation risk from mammography
Is there a risk from radiation?
In Breast Test Wales (BTW) we use mammography to detect breast cancer. This involves passing radiation (X-rays) through your breast to form a picture (mammogram). Radiation can cause cancer, but the risk from mammography is very low. The benefit far outweighs the radiation risk. The number of lives saved by detecting and treating breast cancer is much greater than the number of lives that may be lost because of cancer caused by radiation.
What do we do to minimise the risk?
The amount of radiation is referred to as the dose. The lower the dose, the smaller the risk. However, if the dose is too low the mammogram may not be clear enough to show whether cancer is present. We monitor our equipment to ensure that the correct balance is struck between the dose and the quality of the mammogram. Doses from all our equipment comply with UK standards. We also minimise unnecessary radiation dose by ensuring that very few mammograms need to be repeated.
How is radiation dose described?
The accepted measure of dose in mammography is the mean glandular dose (MGD), which is the average dose to the glandular tissues of the breast. It is expressed in units of milligray (mGy). The dose depends on the size and type of breast.
How is radiation risk described?
Radiation does not cause breast cancer immediately, but it slightly increases the chance that a cancer may arise several years later. The “lifetime risk” is the chance of a cancer arising during the remainder of your life. The risk therefore depends on your age when you are exposed to radiation – the risk at age 70 is less than half the risk at age 50.
How big is the risk?
The risk from mammography is very low. The measured dose can be used to estimate the risk to a 60 year old woman as follows:
Average value of MGD for a two-view mammogram in BTW: 4.4 mGy
Lifetime risk of cancer being caused by radiation: about 10 per million per mGy
So the lifetime risk of the mammogram causing cancer in this woman is about 44 per million, or 1 in 23,000.
How does the risk compare with the benefit?
To put the risk of 1 in 23,000 into perspective, of every 23,000 women aged 60 who have breast screening in BTW about 200 already have cancers that will be detected by the mammogram.
How does the risk from mammography compare with other risks?
Things that expose you to about the same radiation risk include:
- A few months of natural background radiation (or a few weeks in Cornwall)
- Flying from Cardiff to Australia and back
Other activities with roughly the same risk include:
- Driving about 3000 miles by car
- Being aged 40 for about a week (risks from everyday activities, illness etc)
What is the effect of having many X-ray examinations?
Each individual X-ray examination carries its own level of risk. To estimate the effect of having many examinations, the risks are simply added together. It does not make any difference whether the examinations are all done in one day or spread over many years, the total risk is the same.
What about mammography during pregnancy?
In mammography, the radiation is directed only at your breast. The risk to a baby in the womb is negligible. However, if you think you may be pregnant and have any concerns about the risk, please discuss these with us before having your mammogram.
Sources of information used in preparing this information leaflet:
British Medical Association The BMA guide to living with risk 1990 ( London : Penguin Books) ISBN 0 14 012504 3
National Radiological Protection Board X-rays: how safe are they? May 2001 (Chilton: NRPB)
NHS Breast Screening Programme Publication No 54:Review of radiation risk in breast screening February 2003 (Sheffield: NHS Cancer Screening Programmes) ISBN 1 871997 99 2
