[ RadSafe ] Hospital workers subject to excessive radiation

Robert Barish robbarish at verizon.net
Tue Jan 21 16:29:59 CST 2014

As someone who has designed the shielding for many medical facilities as my exclusive work over the past fifteen years, I offer the following observation:

The CT in an emergency department is generally the most used CT scanner in a hospital because it scans trauma patients who come to an ER in greater volume than regularly scheduled patients in a diagnostic radiology department.

Based on multiple room configuration that I have seen, the weekly unshielded dose at the position of the operators would be on the order of 3 mGy.

With no added lead, the attenuation afforded by two layers of ordinary gypsum wallboard at the typical high kV used for these machines would be about the equivalent of approximately 0.15 mm of lead, total. This would reduce the exposures to 1.2 mGy per week. Assuming an annual 50 weeks of work, the operators would receive a yearly dose of 60 mGy.

As the American subscribers to this list know, the permissible annual exposure for radiation workers is 50 mGy although most regulators and hospital radiation safety personnel require ALARA design dose limits of one-tenth that value, i.e., 5 mGy.

But unless the wall between the scanner and the operators was something considerably less substantial than the typical two-layers of 14 mm gypsum wallboard (separated by the usual metal studs), the exposures received would be only somewhat greater than the legal limits and certainly not high enough to cause noticeable radiation effects in the workers in the short term.

Still, the failure to properly construct and then survey the finished room is well outside normal practice.

Robert Barish, PhD, CHP, FAAPM

Shielding Design Physicist

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