How much extra radiation exposure comes from a chest x-ray?

This was a question from a mom of a patient, for whom we both agreed a chest x-ray to rule out pneumonia would have been a good step. Excellent information can be found at http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray#3. To quote, "in simple terms, we can compare the radiation exposure from one chest x-ray as equivalent to the amount of radiation exposure one experiences from our natural surroundings in 10 days." From the same table, a CT scan of the sinuses exposes patients to 0.6 mSv, which is comparable to 2 months exposure. Finally, a CT scan of the chest or abdomen exposes patients to 10 mSv, which is comparable to 3 years of exposure. For me and my patients, the bottom line is to order CT scans only when medically necessary.