Answer to Question #115 Submitted to "Ask the Experts"

Q

How much exposure do a typical chest and abdominal x ray deliver to an 18-month-old child weighing 23 lbs?

A

To answer your question, I used Rosenstein’s Tables (in a pamphlet from the Food and Drug Administration, HEW Publication 79-8079). The tables have information for newborns, one-year-olds and five-year-olds. For the information I’m providing, I used the tables for a one-year-old. I’ll give two sets of numbers for the chest x ray because the child may have had his/her back to the film (AP projection) or may have had his/her chest toward the film (PA projection) so the numbers differ slightly. I’ve also estimated the entrance skin exposure to be 7 mR; this is for an average-size child. In the AP projection, the thyroid and lung would receive 4 mrad, bone marrow 1 mrad, and total body 2 mrad. In the PA projection, the lung still receives 4 mrad, the thyroid and bone marrow receive 1 mrad, and the total body 2 mrad--very slight differences and since these calculations are estimates based on an average one-year-old, they are essentially equal. For the abdominal x ray, I’ve assumed an AP projection; the child is lying on the x-ray table with the x-ray tube overhead (this would be typical). These calculations are based on an entrance skin exposure of 90 mR: the bone marrow would receive 10 mrad, lung 5 mrad, testes 9 mrad, ovaries 35 mrad, and total body 18 mrad. All doses are below those known to cause biological effects. Thank you for the question. Kelly Classic Certified Medical Health Physicist