Hi there,
Yes CT's can deliver a significant dose of radiation, but so can a whole range of other things, including just living. It is one of those thing where we have to balance cost versus benefit. There are also a lot of assumptions being made that people don't get told. The big assumption is that there is a linear relationship between radiation dose received and cancer risk. That appears to hold true for high doses of radiation and the evidence for this comes from atomic bomb survivors and nuclear accident survivors. When it is low doses the evidence is less clear. Most dose response curves for radiation or chemical expose look like a flattened letter 'S'. At low dose there is little response, then it goes through a region where the response is linear, then it flattens off. The problem is that you can't predict from the linear part of the curve, what will happen down at low dose, and collecting data at low dose is difficult and takes a long time.
All of us are exposed to radiation all the time - it is called the background radiation. It ranges, depending on where you live, from 1 - 3 milli Sieverts a year. (A Sievert is the measure of the biological effects of radiation - shortened to Sv). Flying from Sydney to Singapore delivers about 17 micro Sv. From Sydney to London about 60 micro Sv. Flights crews build up about 5 milli Sv for each 1000 hours of flying.
A standard chest X-ray is about 0.1 milli Sv, or 100 micro Sv. A full body CT is about 10 milli Sv (3 - 4 times background radiation) and a mammogram is about 3 milli Sv. Balanced against that is the benefit is terms of better imaging and diagnosis. Does this increase cancer risk. The correct answer is that we do not know, it might, so it pays to be cautious. Is MRI safe - again we do not know as MRI involves fluctuating magnetic field and radio-frequency radiation. At this stage there is no good evidence that these may have cancerous side effects, but many people believe that they could. So it plays to be cautious there as well.
So, as said before, there is huge benefit from these procedures, but there is also some risk. The question is more like, 'if these procedures can help give me a good quality of life for the next ten, twenty, thirty or forty years, with some small risk of a second cancer in that time, whereas the alternative is to die from cancer in five years, which will I choose?' . To me that's a bit of a no-brainer.
Cheers
Sailor
Even with the best charts, we are cautious about fixing our position, for it is so easy to goof. And the easiest way of all is by taking a mark, assuming it is the right one, and ignoring any others that may be in sight.
Patrick Ellam
