|
Dosimetry for X-Ray Users
Radiation Exposure Limits
Occupational dose limits are set in regulation to protect people who work with ionizing
radiation (WAC 246-221-010). The limit for X-ray operators is 5 rem/year (or 5000
millirem/year). The limit is expressed as Total Effective Dose Equivalent (TEDE), which is
a scientific way of determining how doses to a part of the body affect the person as a
whole. Limits are also set for specific organs: 15 rem/year to the eyes and 50 rem/year to
the extremities, which include fingers, feet, or the skin. The best way to determine how
much exposure a person receives over a long time period is through the use of personal dosimetry.
How to Monitor Using Dosimetry
There are three types of personal dosimeters: film "badges," the
new Luxel technology, and TLDs
(thermoluminescent dosimeters). Each can be useful for different needs. These are used and
analyzed on a monthly or quarterly basis (quarterly tends to be cheaper). If you use a
quarterly monitoring period, we recommend you use TLDs or the Luxel type and not film from the service
vendor you are using. Issues relevant to selecting dosimetry for radiation monitoring
include:
- The company or vendor (NVLAP certified)
- The type of dosimetry you need (x-ray, isotopes, etc.)
- Number of staff to be "badged"
- Monthly or Quarterly monitoring period
- Need for extremity monitoring?
Dosimeters do NOT provide an instantaneous exposure reading. In practice, they are worn
for a specific time period, returned to the company for processing/analysis, and the
results reported back to you in a written form. Dosimeters do NOT protect or shield anyone
from radiation exposure; they merely inform how much radiation (if any) that the wearer
received. (See a listing of dosimeter service providers).
The Control Badge
With the monthly or quarterly service, a "control" (or baseline) dosimeter will be
provided, which must be kept in a known radiation-free area (i.e., away from x-ray
machine's beam and scatter area, and NOT in the "control booth!") during the
period when the other badges are worn by staff. The purpose is to measure any
"background" exposure (radiation picked up during mail transit, due to cosmic
rays, and other unavoidable radiation from the naturally occurring isotopes in certain
building materials, and the soil and rock in our environment) which is separate from the
exposure a person gets from occupational work. Using a control ensures that ONLY the
exposure (if any) due to occupational duties is reported to you.
The Lead Apron
If a leaded apron is worn for x-ray work (i.e., mobile x-ray, fluoroscopy), and you are
assigned a dosimeter, you should wear it OUTSIDE of the apron at the collar/neck region,
so that exposure to your head, neck, eyes and thyroid can be measured. If the dosimeter is
worn under the apron, it will be shielded and will not record the dose to your exposed
body parts. If two clearly designated (inner and outer) dosimeters are assigned to a
apron-wearing worker, one can be worn inside the apron. In fact, this is the ideal
protocol for pregnant x-ray operators.
Who Has to be Monitored?
Three types of workers are required to use personal dosimetry: 1) anyone who works with
radiation and actually gets or might get 10% of the annual limit (0.5 rem/year), 2) minors
or declared pregnant women who work with radioactive materials or radiation-producing
machines, and 3) anyone who enters a High Radiation Area (defined in WAC, this is only
relevant to nuclear power plants, linac rooms (radiation therapy) or other heavy
industrial users). Dental facilities generally aren't required to provide dosimeters to
staff since the exposures are very low and the beam sizes are very small. Many physicians
offices and chiropractors also do not have to provide dosimetry, usually because the
x-ray
operator is required to stand in a lead-shielded booth. Even if not required, it can be a
good idea to use a film badge or TLD service as a permanent documentation
reference; the service can be used for a short time (6-12 months) to verify and
record the low (or zero) exposure working environment. You must keep the records
indefinitely, however (WAC
246-221-090).
Report Review
For each time period report, results must be reviewed and compared to regulatory
standards and individual exposure histories. If a report is out of the
ordinary (too high), then it is necessary to find out why the exposure is abnormal, and correct the
problem to ensure the lowest reasonable and compliant levels. Circulate,
distribute, or post the results so everyone knows what their exposure was.
 NOTIFICATION (WAC
246-221-250 and -260). Facilities are required to notify the Department of Health,
Radiation Protection Office (206-682-5327) of exposures that exceed the regulatory
limits (see Radiation Exposure Limits). Depending on the severity of the overexposure,
immediate notification or 24-hour notification is required.
Top
Ten Dosimeter Do's and Dont's
-
DO WEAR IT when working. Of what value is it if it is in a locker or purse?
- DON'T WEAR IT when you are receiving x-rays for your own personal health care.
- DON'T WEAR IT away from the workplace.
- DON'T WEAR IT under your apron (unless using more than one dosimeter).
- DO TURN IT IN promptly. Time gaps make analysis more difficult, less accurate, and
reduces the legal and historical value of the reports.
- DO REPORT A LOST/DAMAGED unit immediately (sunshine/heat, the washer, etc.). Prevent
damage by not leaving your monitor in areas of high temperature.
- DO PLACE the control in a radiation-safe area; this affects the accuracy of all
dosimeters!
- DON'T PLACE one in an area for testing (operator booth, receptionist's desk, etc.).
Additional badges for testing can be assigned and provided by the service.
- DON'T SHARE one; this is illegal. An exposure total for a shared dosimeter is
meaningless to each individual.
- DON'T TAMPER with your badge or anyone else's. The reports are legal documents and are
regarded as real exposures received.
Contact Information
X-Ray Control Section -- Ellen G.
Haars, Supervisor
More information is available from:
X-Ray Control Program
Washington State Department of Health
Post Office Box 47827
Olympia, WA 98504-7827
(360) 236-3231 or 1800-299-XRAY
|
