Get checked out - have a full body CT?

March 27, 2014 By: Bjorn Rembacken

Get checked out - have a full body CT?

Since my teenage years I have been afraid of radiation. Two phrases stuck in my mind: 1) “there is no safe limit for radiation exposure”, 2) “the DNA damage is cumulative and never goes away” ...

Indeed this is why I see little point in radiology for disease which can be assessed by endoscopic means.  For the same reason I am incredulous when people voluntarily expose themselves to ionising radiation as part of a health check-up.

During ERCP I diligently carried my personal radiation exposure meter for many years.  Although the device was issued for “exposure prone activities”, such as ERCP, I decided to always carry the meter with me at work.  After all, the ionising radiation is even more significant when not shielded by a lead apron. 

Last year I had an Eureka moment and also started to wear the dosimeter during flights.  In the UK the average annual background radiation dose is 2.2 millisieverts (mSv).  However, at cruising altitude (35.000 feet), the hourly radiation may be up to 50 times greater than at the surface.  In addition, those body scanners which are replacing metal detectors at airports also emit radiation.

Your precise dose depends on the number of hours spent at high altitude and the latitude of the flight.  Latitude is important as earth's magnetic field deflects charged particles. The shielding is most effective at the equator where earth's magnetic lines are parallel to earth’s surface. Conversely, the magnetic shielding disappears over the poles where the magnetic lines point perpendicular to the surface.  Not sure how do penguins manage to cope with the large amount of radiation they receive at the South Pole?  Perhaps they don't live long enough to get cancer? 

For every 200 hours in the air, you receive 1 mSv of radiation exposure (look for yourself by clicking this link).  I was therefore surprised that our radiation protection officer did not phone me after I had travelled with my radiation exposure meter for year.  It turns out that most of the radiation received in an aircraft is from neutrons which can not be detected with classical dosimeter!

Official calculations estimate that for each 1 mSv of radiation exposure (above background radiation), will give rise to another 6.3 cancers per 100.000 people/year.  It is for this reason that EU-based air crews are limited to a maximum of 100 mSv of exposure in every 5 year period.  Nevertheless, there is evidently no safe radiation limit as pilots have been found to have an increased risk of cancer. 

My Radiologist friend tried his best to reassure me and pointed out that these radiation figures must be put into context.  “For example, a trip to Mars, will give you a total of 1000 mSv  which will give you a 1:20 extra risk of dying from cancer”.   In comparison, one of our abdominal CT studies only generate some 10mSv of radiation and will not cause more than one extra cancer in 400-500 exposures…

Reassuring words indeed !

About the author

Bjorn Rembacken is at Leeds Teaching Hospitals NHS Trust, Leeds, UK. He was born in Sweden and qualified from Leicester University in 1987. He undertook his postgraduate education in Leicester and in Leeds. His MD was dedicated to inflammatory bowel disease. Dr Rembacken was appointed Consultant Gastroenterologist, Honorary Lecturer at Leeds University and Endoscopy Training Lead in 2005. Follow Bjorn on Twitter @Bjorn_Rembacken

 

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