Answer to Question #12236 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT

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

Q

I understand that x-ray tube leakage is negligible. Do you have any information on collimator leakage? My child was positioned about 8 centimeters (cm) from a collimator during an x ray. I read some information online that sometimes, although rarely, the blades can leak radiation. If so, what is the average level of leakage?

A

Any leakage from the collimator is the same as leakage from anywhere around the x-ray tube housing. The lead shielding in the housing and the collimator blades are thick enough to stop most of the radiation, and the very small amount that gets through is the leakage radiation.

A reliable reference notes that "leakage radiation is radiation that passes through the lead shielding in the tube housing when the beam is turned on." Also, "leakage radiation occurs whenever the x-ray beam is 'on.' It is completely independent of the useful beam itself and will occur even if the collimator shutter is completely closed. As long as x-rays are being generated within the tube housing, leakage radiation occurs." (Curry et al. 1984)

Kennith "Duke" Lovins, CHP

Reference

Curry TS, Dowdey JE, Murray RC. Christensen's introduction to the physics of diagnostic radiology. 3rd ed. Philadelphia: Lea and Febiger; 1984: 413.

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