To the Editor
Ideally, a radiation safety expert would perform a comprehensive survey of any individual potentially contaminated with radioactive material.1 However, during a large-scale incident this may be impractical, and hospitals should plan to screen large numbers of patients using fixed and hand-held survey meters.2 While operator fatigue and the time required to perform a thorough examination are the major limitations of hand-held survey meters, logistical challenges with portal detectors include limitations of sensitivity at very low levels of contamination and potential alarming by sources other than contamination of the individuals being screened.3
In their exploratory study, Dr. Salen and colleagues4 randomized patients to undergo manual screening with a standard hand-held Geiger counter or to walk through a portal monitor, concluding that Geiger counter screening was more sensitive than, and equally specific to, radiation detection portal screening in searching for radioactively labeled subjects.
We are concerned that the screening techniques featured the strengths of the Geiger counter survey and the shortcomings of portal monitoring. Specifically, examiners could predict where to look for the radiation sources and were able to place the Geiger counter right against the source with no shielding between the survey meter and the cesium-137 source. Placement of the test source in unpredictable places such as the bottom of one’s shoes would be a more realistic scenario.
In contrast, in the portal monitor group, the sources placed on the victims’ backs were shielded from the portal monitor by the individual’s body. The programmed sensitivity of detecting a 1.0-μCi cesium-137 source in a 10 μR/hr background does not include detection through shielding. The post hoc analysis where this shielding geometry was eliminated yielded 100% detection.
Finally, detecting high activity sources is more relevant following a contaminating radiologic event5 and the relevance of failing to detect a 10-μCi source during mass screening is questionable. The first priority should be to detect high active sources, followed by identifying significant radioactive contamination (> 5 mrem/hr) on people who will need rapid decontamination and screening for internal contamination, and finally, if feasible, screening for contamination near the levels assessed in this study. We therefore recommend the use of both of these important tools in a complementary fashion in a mass casualty situation.