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19 July 2008

Answer to Question #5223 Submitted to "Ask the Experts"

Category: Security Screening — Airport Screening

The following question was answered by an expert in the appropriate field:

Shipment of blood products via airports currently have "do not x ray" stickers affixed to the package. Many airlines and airports in compliance with TSA (Transportation Security Agency) guidelines are requiring visual and hand inspection of packages that have this designation. To prevent contamination of sterile blood products as well as to observe security procedures, the possibility of x-ray screening of blood products was introduced. The concern is that the blood cells, specifically, the T-lymphocytes, will undergo some change which will alter their function as a result of the low-dose radiation received from airport check-in luggage/cargo x-ray equipment. Is there evidence that says otherwise? The only thing I found was from Petzer, et al., from Blood, 2002.

Very interesting question. Immature T cells are quite sensitive to radiation. One gray (1 Gy, gray is a unit of radiation dose) can trigger rapid apoptosis in and out of the body. Mature T cells are much less sensitive.

What is very interesting is that, often, blood products are intentionally irradiated to very high doses to prevent graft versus host disease which occurs when lymphocytes mount an attack on the healthy tissue of the recipient of the blood product. In this case, blood products are exposed to approximately 25-35 Gy or more.

I talked to one of our radiation oncologists and our radiation biologist. Both agreed that at high doses (minimally about 1 Gy) apoptosis was induced in lymphocytes. At the levels of radiation exposure due to security screening (0.00001 Gy for a baggage screening system to 0.0005 Gy for a cargo container screening system), the induction of apoptosis is very unlikely, but remember that few have really looked at such low doses causing effects on lymphocytes. These doses are on the order of daily background radiation.

So, what I learned from our radiation oncologist and radiation biologist is right in line with the conclusions of Petzer, et al.—that blood products can be screened for security purposes.

Kelly Classic
Certified Medical Health Physicist

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