Radiography Risk

There's lots of data about the dangers of CT scans, and we certainly do a lot of scans in the Emergency Department. Although not specifically mentioned in the CEM syllabus, I think it is an unspoken part of every test we request, especially head CTs. I don't think we quite "order numerous CT scans each shift, and dole out radiation exposure dwarfing the atomic bomb dropped on Hiroshima" but we are getting closer than we used to! Just as the sports medics are reducing the number of scans they do, so do we need to.

If you're like me and don't know a lot about radiation, PEMMorsels has a good introduction, as does the Short Coat:

• 1 Sv= 100 rem.  We use milliSieverts in most medical imaging.
• Neoplasms have typically been associated with radiation in excess of 50 mSv
• Background radiation = 3.5 mSv/year 
• Background Cancer Incidence = 420:1000 (42%)
• Medical radiation is between 0-100 mSv

 Although x-rays have a radiation risk, we worry more about the risk of CTs - as summarised on LITFL:

• Routine abdominal CT scan estimated exposure quoted as 8-10 mSv
• Actual calculated radiation: Average 11-20 mSv (Range 4-45 mSv)
• Multiphase abdomen and pelvis CT scanning: median 31 mSv (Range 6-90 mSv)
• Chest CT for suspected pulmonary embolus: median 10 mSv (Range 2-30 mSv)
• Routine head CT median:  2-3 mSv (Range 0.3-6 mSv)

With these radiation doses, we might easily be causing pathology:

• 2-3 brain CT triples the risk of brain tumours
• 5-10 brain CTs triples the risk of leukaemia
• Per 10,000 patients, a head CT might cause a brain tumour and leukaemia in one person. 
• At 10 mSv Lifetime Attributable Risk of developing a cancer is 1:1000 
• One additional cancer for every 4000 CT heads.  

So, as Clinicians we need to be able to balance the risk of a CT vs the risk of undiagnosed disease. Especially in children, the views of the parents often play a part in our decision making process, and maybe we should be gaining consent. If you'd like to be able to instantly show your patients their risk of cancer from a CT, there is a clear graphical display here, and there is a nice PV card here which unfortunately doesn't cover the paediatric population. X-ray risk has a more precise risk calculator, but again only estimates the risk in children.

And this is the risk if it all goes right! If it goes wrong, the doses could be a lot more.  And if there is a radiation emergency, what would you do?

Times are changing, and we're moving away from CT scans, and towards observation.  So think carefully before you do the CT scan.

All of this is nicely summarised by St Emelyns - there is often no right answer, and you have to balance the risks.