You'll often find charts like this that express the risk of various medical x-rays by relating it to levels of radiation from other sources.

I'm wondering, is this a valid way of thinking about the risk? Because it makes a chest x-ray seem pretty trivial - exposes you to no more radiation than just 5 days of normal living (natural background radiation). Is it really valid to think of risks of chest x-rays in that way or are there additional factors here that would change the equation?

Does the fact that a chest x-ray is 50 msc in one instant make it different and more dangerous than the 50 msc you are exposed to over five days of normal living from background radiation?

I suppose the idea is the total number of photons that impact an area, rather than per time. I guess 1 photon could initiate harm.

The time is a factor; there’s a difference between a chronic and an acute dose. When the exposure is spread out, the body has a chance to heal; this is generally more important for higher doses than what you get in an x-ray. 

 

Yes, a slow rate of ionization means a double stranded break in DNA (the main cause of problems) can be repaired because the sister chromatid will likely have the homologous sequence intact and can be used as a repair template.  And there are other evolved repair methods, too.   If a large dose happens in a quick burst however, there is a much greater chance that flood of photons will leave no homologous sequence intact and then there is likely a serious genomic breakdown leading to tumors or cell death.  

4 hours ago, Alfred001 said:

Is it really valid to think of risks of chest x-rays in that way or are there additional factors here that would change the equation?

It's a risk/benefit calculation. A chest x-ray for a cough, say, is quite different to one for a penetrating chest injury.

It's not uncommon to see push back against a doctor referring a patient for a CT scan if the radiologist (sometimes after being flagged by the radiographer) feels the risk may be too great - particularly for young people and abdominal scans. 

I was a patient of a good doctor and he was in fact a specialist in his area. He told me that if I was worried about x-ray I should not eat anything or go outside because many food was already contaminated by radiation and there is more radiation we are exposed to every day than taking a few x-ray. His comparison made me feel relieved about the x-ray anxiety.