Ionizing radiation worriesmeet arachnophobia

October 20, 2009

Radiologists in Manchester, U.K., and Ghent, Belgium, have carried out highresolution CT on the 50-million-year-old fossilized remains of a spider embedded in amber, according to a report from October 2007 on physorg.com

Radiologists in Manchester, U.K., and Ghent, Belgium, have carried out highresolution CT on the 50-million-year-old fossilized remains of a spider embedded in amber, according to a report from October 2007 on physorg.com. This revelation caused me to ponder spiders. I have plenty at home in the shed, in the loft, certainly in the bath. However, I cannot ever remember seeing a spider in an x-ray department. Flies, wasps, bees-yes, all of these, but never a spider.

Many x-ray departments I have worked in have been located in the hospital basement, surely an ideal home for spiders. But there were none to be seen. The department I work in now is on the sixth floor, so perhaps the dearth of spiders is due to vertigo? Somehow I doubt that. It would be reassuring to think that the absence of arachnids is due to the spectacular cleanliness of hospitals. Looking around my office suggests otherwise, yet the only webs and web crawlers in here are on my PC.

Now I know why. Evidence indicates that the release of radiation from the Chernobyl nuclear reactor has had an enormous impact on the distribution of spiders in the surrounding forests. The number of spiders and webs is less than a quarter than would be expected. Maybe this explains the scarcity of eightlegged creatures in x-ray departments.

The response from arachnophobes may well be: “Good riddance.”

Radiation safety is a big deal not just for spiders. We are entering an era of heightened awareness of the risks of medical irradiation. The Image Gently campaign to promote exposure reduction for pediatric patients (imagegently.org) and the appearance of radiation safety advice on YouTube are two examples of this.

The overall radiation dose to the U.S. population from medical imaging has increased more than sevenfold since the 1980s and now accounts for nearly 50% of all environmental radiation. Radiation exposure from medical procedures is now equivalent to the background radiation dose and it is growing year on year.

For many observers, the widespread use of multislice CT is responsible for this increase. CT may be responsible for 1% of total deaths from cancer, rising to 2% in some pediatric patient groups. No need to tell that to the spiders of Chernobyl, assuming you can find one to tell.

New dose reduction strategies are being developed for pediatric examinations and for high-dose procedures, such as cardiac CT. In addition, radiologists and other clinicians should be adopting a policy of justification when considering the use of ionizing radiation. Knowledge of a patient's imaging history to avoid unnecessary repeat examinations, selection of alternative imaging modalities, and a little bit of clinical common sense are critical to safer imaging.

There are a number of clinical situations where CT is unequivocally the primary tool of choice, and perhaps the only appropriate modality. In other situations, ultrasound may be equally relevant or perhaps even more appropriate. Radiology trainees must become adept at performing ultrasound for acute conditions, particularly in children and young women, for whom the lifetime risk from radiation is higher and in whom ultrasound has the greatest diagnostic potential. If radiologists are to provide a robust urgent and emergency service for these two groups, then they need to be comfortable performing pediatric examinations and confident of their transvaginal ultrasound skills. A straw poll that I conducted at a national meeting for emergency radiologists suggests that this is not the case at present.

Radiologists' increased confidence with CT has perhaps been gained at the expense of their ultrasound skills. The ultrasound unit, and in particular the transvaginal probe, is the only place you are likely to find a spider's web at the weekend. The spider knows it will not be disturbed here!

The spider could actually be a good role model for radiologists. The 14th century Scottish king, Robert Bruce, was apparently inspired to continue fighting the English by the repeated and untiring efforts of a spider that was spinning a web in the face of huge logistical difficulties. If we are not as tireless and diligent as that spider in ensuring the appropriate use of ionizing radiation in medical imaging, then arachnids may not be the only ones to suffer.