Download Screening mammograms and their radiation risks

Risks and benefits
Risks
The risk of getting cancer from a screening
mammogram is considered to be very low.
Table 2 below shows the additional risk in a
person’s lifetime of developing cancer from X-ray
procedures at each examination.
Examination
Lifetime additional risk
of cancer per exam*
Negligible Risk
Chest, teeth, arms &
Less than 1 in 1,000,000
legs,
hands
&
feet
x-rays
Skull, head, neck x-rays
Minimal Risk
1 in 1,000,000 to
1 in 100,000
Very Low Risk
hip, spine, abdomen,
pelvis x-rays, CT head,
breast mammography
1 in 100,000 to
1 in 10,000
Screening
mammograms
and their
radiation risks
If you are pregnant, it is advisable you postpone
your screening mammogram until after the birth.
A screening mammogram is not recommended for
women who suspect they are pregnant.
Benefits
The low dose of radiation used in a screening
mammogram has not been proven to cause
harmful effects. The benefit of early diagnosis and
treatment of breast cancer far outweighs the risk
of the small amount of radiation received during a
screening mammogram.
How often should I have
a mammogram?
At least every two years unless there are reasons
for more frequent mammograms. If breast cancer
is detected early, there is a good chance it can be
treated successfully.
Low Risk
Kidney & bladder [IVU], 1 in 10,000 to 1 in 1,000
Stomach – barium meal,
CT chest, CT abdomen
Table 2
* These risk levels represent very small additions to the
1 in 3 chance we all have of getting cancer throughout
our life time.
www.breastscreen.health.wa.gov.au
© BreastScreen WA, Department of Health 2011
Helping Deliver a Healthy WA
HP10724 JULY ‘11 23468
Source: Adapted from UK National Radiological Protection
Board (2001).
13 20 50
Natural background radiation
Radiation occurs naturally all around us from
sources such as the sun, rocks, soil, buildings,
air, food and drink. This is known as ‘background
radiation dose’.
The scientific unit of measurement for radiation
dose is millisieverts (mSv). In Australia the average
background radiation dose is about 2.0 mSv per
year.
Diagnostic imaging and radiation
X-rays are a form of ionising radiation which
penetrates the body to form pictures on film or
digital imaging (eg. a computer screen). This type
of radiation is used widely in medical facilities to
perform diagnostic imaging procedures.
X-rays provide valuable information about the inside
of your body and are important in helping your
doctor make an accurate diagnosis.
Diagnostic imaging with no radiation
Other forms of diagnostic imaging such as magnetic
resonance imaging (MRI) and ultrasound are
procedures that do not expose you to ionising
radiation.
Radiation exposure
Studies have linked high doses of ionising radiation
(>50mSv) to an increased risk of cancer. Living
cells can be damaged by X-rays. However, the risk
is extremely low with the radiation dose you will
receive from a mammogram.
Table 1 compares the radiation dose of a screening
mammogram, (which involves 2 X-rays of each
breast), to other imaging tests.
Radiology
Typical
effective
dose
(mSv)
Equivalent
period of
natural
background
radiation
X-ray Examination
Chest
0.02
5 days
Mammogram
0.7
24 weeks
Abdomen
0.7
24 weeks
Pelvis
0.7
24 weeks
Lumbar spine
1.0
35 weeks
2.0
1.3 years
8.0
10.0
5.3 years
CT Examination
Head
Chest
Abdomen
6.7 years
Table 1
Source: Towards appropriate use of diagnostic imaging: A
guide for medical practitioners and their patients. Cancer
Council WA, 2011.
Screening mammography
and radiation
A screening mammogram is an X-ray of the breast
tissue for women without any breast symptoms. It
uses low doses of radiation (about 0.7mSv for
4 X-rays).
X-ray safety
X-rays are produced only when a switch is
momentarily turned on, like a light switch. No
radiation remains after the switch is turned off.
BreastScreen WA contracts licensed medical
physicists (a scientist specialising in physics in
medicine) to routinely evaluate the radiation dose
from X-ray equipment used to ensure it is as low
as possible and does not exceed regulatory limits.
Factors affecting X-ray dose
The radiation dose from a screening mammogram
is the amount of X-rays that are absorbed in the
breast tissue. Two of the major factors affecting
radiation dose are the amount of compression
and the thickness and structure of the breast.
Breast compression during a screening
mammogram reduces the radiation dose
significantly since a thinner amount of breast
tissue absorbs less radiation. It also separates
overlapping folds of breast tissue that may
obscure small abnormalities.
Breast implants can block a clear view of the
breast tissue making mammograms less effective
in breast cancer detection.
Therefore, radiation exposure will be greater in
women with implants, because more X-rays need
to be taken (between 6 - 8) and less compression
is used.