How many x-rays do I need?

Since working in a company that specializes in radiation therapy, I find myself more aware of radiation exposure through medical devices. I actively try to shield myself from exposure in the GammaKnife lab; I duck behind others in the CT room; and I avoid unnecessary x-rays and other forms of imaging using ionization radiation. Since imaging procedures are a source of substantive exposure to ionizing radiation,1 I prefer to reduce my cumulative exposure as much as possible.

Radiation from all of the imaging plus what I’ve received from the transatlantic flights I’ve taken probably still don’t add up to too much. Yet I have a hard time being comfortable around these machines. There is very little accessible information. How many procedures do we need to get enough information for diagnosis or treatment? Are images necessary to prescribe a course of action? I find that I am now unable to trust most of my medical providers or their administrative staff. Every recommendation for a diagnostic procedure or treatment sounds to me like a sales pitch, one leaving me always in the uncomfortable situation of having to refuse the offer.

I am just here for my routine procedure, I want to say. And no, just because my insurance company will pay the full cost of the procedure does not mean I’m any more interested in doing it. That’s a horrible way to think about it, that providers should do all they can to squeeze money out of an insurance company, that patients should do all they can to use their insurance benefits, and the insurance companies must fight the abuse from both sides tooth and nail by looking for mistakes and shirking on coverage. I do not want to be caught in the middle of this complicated financial war, where the benefits may not outweigh the cost.

I went to the dentist this morning at a new clinic (first time since moving to Seattle). Upon entering the exam room, I was told that I would be starting with a panoramic radiograph, essentially a CT for my mouth. Since I had never had one done before, I asked about relative radiation exposure. That was when I learned that the dentist also does a 7-image bitewing set in addition to the panorama, and that no one in the office really knew how much exposure I would have from the set of procedures. I decided to refuse all images until I had a change to investigate further, and suggested that I could have my previous set of bitewings (from 6 months ago) sent over if the dentist wanted the information.

Most dentists recommend bitewings for their patients once a year. Coincidentally, this is how often dental images are reimbursed by most health insurers. Do dentists prescribe images because the data supports that yearly exams are key, or because that is how often they are paid for them? I am not arguing against dental radiography, I simply think there is so little information out there to help me, the patient, decide which imaging procedures to get and which ones to refuse. After all, imaging does carry and innate risk, and dental x-rays in particular may contribute to increased incidence of brain cancer.2 I want to make sure the benefits I get from these procedures outweigh those risks.

So what are the risks? Here are the ranges of effective doses calculated by Ludlow et al in 2008.3 These values were significantly higher than previous suggested doses, which used lower ICRP (International Commission on Radiological Protection) proposed weighting factors for tissues. These days, with digital x-rays, the effective dose will be even lower for bitewings, somewhere around 10-20% of the values below. This reduction does not apply to the panaramas, which are already digital.

Effective dose* (mSv) Cost ($USD)
Single bitewing x-ray 0.005 15-25
Four bitewings 0.020 50-100
Full mouth series
(18 bitewings)
0.035-0.171
(0.388 for slower film speeds)
100-200
Panoramic 0.014-0.024 100-200

Not so bad. These doses are fairly reasonable. To put things in perspective, a single bitewing gives you excess radiation equivalent to what you would receive from a week in Denver. The full mouth series is approximately equivalent to a chest x-ray, although of course, the tissues exposed are different. Whether or not these values are precise or correct remains to be seen. It seems that each study produces some variation on these doses.

Ultimately, it is up to the patient to determine whether or not these are reasonable risks. Radiation exposure is cumulative, and one should be aware that the effects are seen over a lifetime. It may be prudent to assess the benefits of each imaging procedure, and realize that not every one may be necessary to proper treatment and care.

*What is effective dose? It is the average dose weighted by the types of tissues receiving that dose. Different tissues are more or less sensitive to radiation. For example, the gonads, thyroid, bone marrow, and other glandular structures are more sensitive and will be weighted more, and hard bone surfaces which are less sensitive are weighted less. The effective dose gives a better sense of how much increased risk accompanies the particular radiation exposure.


1Fazel, R. et al. “Exposure to Low-Dose Ionizing Radiation from Medical Imaging Procedures.” The New England Journal of Medicine. Vol. 361, pp. 849-857, 2009.

2Claus, E. B. et al. “Dental x-rays and risk of meningioma.” Cancer. Vol. 118, Iss. 18, pp. 4530-4537, 2012.

3Ludlow, J. B. et al. “Patient Risk Related to Common Dental Radiographic Examinations.” The Journal of the American Dental Association. Vol. 139, pp. 1237-1243, 2008.

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