**Caltech’s whole body dose limit for planned exposures is 500 mrem/year (5 mSv/yr). If a Caltech worker were to receive the maximum allowable planned dose each year for twenty years, the total dose received would be 10 rem (0.1 Sv). According to the BEIR V report, the worker’s chance of death from cancer would increase by approximately 0.4%. This is fairly small compared to the normal chance of death from cancer in the U. S. of about 20%.
** Note: for x-rays, 1 Rem = 1 Roentgen, ibid.
With one more important piece of information, namely that medical X-ray is measured by the mR in air at skin entrance (rather than by tissue or bone marrow dose as used by the physicist), I will telescope some ten years of research into a few short conclusions:
For X-ray of arms or legs, and dental X-ray, it requires an accumulated dose of 4000 mR to increase the risk of non-lymphatic leukemia the same amount as one year of natural aging.
For chest X-ray, it requires an accumulated dose of 1670 mR at skin entrance to simulate one year’s natural aging for increasing non-lymphatic leukemia rate. **
The source provided by samclem (
http://www.fda.gov/cdrh/consumer/TVRad.html) states that the current standard (mandatory in the US from June 1, 1971) was 0.5 milliRoentgen/hour; but it doesn’t state how far away from the set this is measured (important due to inverse-square law) or what the situation was prior to 1968.
But we’re on the right track.