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X-Ray Dose-Measuring Service for Physicians and Dentists
January 21, 2001



        o  The entrance dose of x-rays is the dose received at the body's surface, where the x-ray beam enters. The exit dose, which is what results in an image, is very much lower. The body absorbs the difference between the entrance and exit doses.

        o  TLDs (ThermoLuminescent Dosimeters) can measure the x-ray entrance dose received by any patient during an x-ray imaging procedure. TLDs are small, nearly flat crystals (about the diameter of a pencil eraser), sometimes with a self-adhesive back.

        o  On the patient's skin, in the field where the x-ray beam will hit, the x-ray technician just tapes the TLD. The TLD does not interfere with the image. After the x-ray procedure, the irradiated TLDs are sent to a "reading" machine which reveals the entrance dose.

        o  X-ray practitioners can obtain the TLDs, the instructions, and the reading service by mail from an accredited laboratory at the University of Wisconsin:

Radiation Monitoring by Mail
Univ. of Wisconsin Radiation Calibration Lab
1530 Medical Sciences Center
1300 University Avenue
Madison WI 53706-1532.

Tel: 608-262-6320
Dr. Larry Dewerd, or Keith A. Kunugi.
E-mail: kakunugi@facstaff.wisc.edu

        o  TLDs are inexpensive (probably less than $3 each), but they are useless without a laboratory's services (instructing, shipping, reading, record-keeping, supplying and reading the control-TLD which measures the radiation exposure accumulated from natural sources by each batch of TLDs before and after the x-ray exposure). These services cost more than the TLDs themselves. There are probably reduced fees for volume.

        o  For fluoroscopy machines, "real-time" (immediate) dose-measuring equipment has been available for decades, and is highly recommended, because of the high doses delivered by an x-ray beam which stays "on" continuously for many seconds, even for many minutes. Such equipment tells the fluoroscopist the x-ray dose already accumulated by the patient's surface from fluoroscopy at any instant during a procedure.

X-rays and Health
Committee for Nuclear Responsibility, Inc.
PO Box 421993
San Francisco CA 94142-1993
www.x-raysandhealth.org
January 2001



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