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Radiation Exposure - Should I get that scan?

Chris Ball - Thursday, February 23, 2017

Should I get that scan? 
Getting a scan sounds simple and straightforward but it is actually a more complex decision than most people would be aware. Using my own experience working in sports medicine, I order many scans. I am requested to order more than are required from my perspective while patients refuse others I consider necessary. There are a several important issues to consider when having a scan but the two main ones are:

1. Radiation exposure 
2. Utility of the test. 
 
In this blog I will discuss radiation exposure and in the following I will discuss test utility. 
 
What is radiation?
Radiation is the emission or transmission of energy in the form of waves or particles through space or through a medium. Light and sound are forms of radiation but are considered non-ionising radiation. This means that although light and sound can travel through structures in our body they are not strong enough to break down any of the chemical bonds in the molecules that make up our cells. Ionizing radiation however is radiation which is strong enough to change the subatomic structure of a molecule and leave it “ionised”. Ionising radiation has been shown to cause some changes in cells and increases the risk of cancer. Sunlight is a good example of this difference. Normal light poses no risk to the human body but UV radiation from the sun is a type of radiation which all North Queenslanders will understand is associated with sunburn, melanoma and other skin cancers.

What dose of ionising radiation do common scans emit?
When determining the safety of having a scan it is important to understand the radiation dose emitted by the scan. This level needs to be considered in context of understanding theradiation dose we are all exposed to daily due to our environment (background radiation dose) and the level of radiation dose considered to be harmful.

--

"We are exposed to radiation
from natural sources all the
time. Estimates show that
an average person receives
an effective does of about
3mSv per year (Sv or Sievert
is the unit for absorbed dose)
from naturally occurring
radioactive materials and
even cosmic radiation from
outer space."
--

We are exposed to radiation from natural sources all the time. Estimates show that an average person receives an effective dose of about 3mSv per year (Sv or Sievert is the unit for absorbed dose) from naturally occurring radioactive materials and even cosmic radiation from outer space. These natural “background” doses vary throughout the world but 3mSv is considered the average background dose. This means that if you are exposed to a 3mSv dose of radiation at one time, it is equivalent to a year’s worth of background radiation. It is hard to put a number on how much radiation is safe or what dose will cause health problems. People have different genetics and different susceptibilities to different cancers so estimates need to be made. Below is a table which outlines ionising radiation dose from various imaging modalities and the associated increased risk of cancer with them.



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