Answer to Question #5088 Submitted to "Ask the Experts"

A few years back I had to lie on my back while the x-ray equipment was lined up almost directly above my gonads in order to take a lower back x ray for a new job requirement, not an injury. While it seems that previous answers to similar questions indicate that most one-time x rays are extremely safe, I'm concerned because I am a male, have not had children yet, and it seems that direct radiation could cause genetic defects in offspring. It was a small clinic in California and I'm not sure if they are still in business so I could find out what level of radiation was used, but it was just one quick x ray. I was not offered a shield. Because of the location of the beam, should I be concerned about genetic damage that I could pass on or are lower-back x rays typically taken without shields?

First, a gonad shield probably could have been used with this exam. I say probably because I can't know the exact nature of what was done. Our facility normally uses gonadal shielding but mostly to reassure the patient. But generally men can have their gonads shielded for lower back exams. I am not particularly surprised that it was not done, because the impression you expressed is correct. Most one-time x-ray exposures are considered to be extremely safe.
Also I should say that radiation-induced genetic defects have not been observed in humans (NCRP 2000)¹. The offspring of the survivors of the atomic bombings at Hiroshima and Nagasaki to date have not had genetic defects at a statistically higher rate than the general population of Japan.

1995 data from the National Exposure X-ray Trends data base (CRCPD 2001)² indicates a lateral spine exam average entrance skin exposure was 370 millirem. Your exposure could certainly have been higher or lower.

The International Commission on Radiological Protection produced an estimate of the probability of severe heredity effect of 0.00013 per rad (ICRP 1990)³. A roentgen is a unit of exposure and a rad is a unit of absorbed dose. In this case the relationship is probably about 0.90 rads to a roentgen (Bushberg et al. 2001)⁴.

I should further point out that that estimate is based on animal data from exposures at much higher dose levels than occur in such diagnostic procedures as the one you had. It is not at all certain that there is any increased probability of genetic harm at the level of such diagnostic procedures. But assuming there is an increased risk it would be estimated to be on the order of 4.3 out of 100,000. The math is 0.00013 X 370/1000 X 0.90 = 0.000043. The first term would be chances per rad, the second the fraction of a roentgen the dose was estimated to be, and the third the conversion from roentgens to rads.

I am inclined to say that there is no chance that the radiation dose you received could cause an unfavorable genetic problem; however, I can't quite say that. But I can honestly say that it is extremely unlikely to cause any genetic problem in a child you might father in the future. Further, as the time between the dose and having a child increases the extremely small probability, if it exists at all, of a genetic disorder resulting from that dose probably decreases.

I would not worry about it.

Peter G. Vernig

References
¹National Council on Radiation Protection and Measurements. Radiation protection for procedures performed outside the radiology department. Bethesda, MD: NCRP Report No. 133:53; 2000.

²National Evaluation of X-ray Trends (NEXT). 1995 abdomen and LS spine x-ray data. Conference of Radiation Control Program Directors and Center for Devices and Radiological Health. Rev. 5/16/01.

³International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection. pg 22; New York; 1990.

⁴Bushberg JT, Boone JM, Seibert JA, Leidholdt JM. The essential physics of medical imaging, 2nd ed., Williams & Wilkins; pp 52-55; 2001.