This past fall, I took an introductory course in Principles of Epidemiology. We were discussing study design, and the issue of exclusion criteria. In one of our examples, subjects with spondylitis (my particular form of arthritis) were excluded from a study about bladder cancer. My professor asked why people with this condition might be excluded from the study. Of course, my hand shot up immediately because I knew the answer: multiple x-rays. That is, people with spondylitis have an abnormal amount of x-rays in their pelvic and hip region and are at a higher risk for bladder cancer. They don't represent subjects with 'normal' exposure.
After this class it suddenly occurred to me that I was in this higher risk category. I had never really thought about my condition in this way before. To date, while it's been irritating and has had an impact on my life to an extent, it never really made me feel anxious about my overall health prospects because my case is comparatively mild and while there's no cure, it's probably not going to kill me. I'm much more afraid of swine flu, or cancer, or Hanta virus, or water scarcity causing global unrest.
But suddenly I've been much more cognizant of the number of x-rays that I am prescribed. Rheumatologists love to send me to the radiology lab--dentists love to give me the bitewing x-rays--and of course there are mammograms (and while the researchers are arguing about whether women should start at age 40 or 50 for annual screening mammograms, most obgyns follow the recommendations that send patients at age 40).
So I've spent the last week or so reading up on radiation and risk, and found that there are some interesting tools that one can use to calculate your annual radiation dose.
Here is the EPA's calculator:
Here is one from the American Nuclear Society:
And yet another one by the Neighborhood Environmental Watch Network:
Some of the questions they ask to calculate exposure are pretty interesting. I'm not sure, for example, if I live within 50 miles of a nuclear power plant or a coal-fired power plant. I never really thought about how living in the Colorado Plateau gives you 63 mrems a year (as opposed to 16 mrems on the Atlantic coast). Having a gas camping lantern gives you 0.2 mrems annually and sharing a bed with someone gives you 1 mrem.
Here's what the American Nuclear Society says about dose:
The average dose per person from all sources is about 360 mrems per year. It is not, however, uncommon for any of us to receive far more than that in a given year (largely due to medical procedures we may undergo). International Standards allow exposure to as much as 5,000 mrems a year for those who work with and around radioactive material.Because of my x-rays, my dose is twice as much as the norm. But I'm comforted by the fact that it's 4,373.93 rmems less than the allowable annual maximum permissible dose under the (somewhat frighteningly generous) International Standards.