2721 Radiation Monitoring

Personnel Monitoring

• Personnel dosimetry: Refers to the monitoring of equivalent dose to any person occupationally exposed on a regular basis to ionizing radiation, which is recommended

• It is required, however, whenever radiation workers are likely to risk receiving 10% or more of the annual occupational EfD limit to 50 mSv (5 rem) in any single year as a consequence of their work related activities

• Personal Dosimeter

  • Provides an indication of the working habits and working conditions

  • Determines occupational exposure

  • Does not protect the wearer from exposure

• Consistency of location in wearing the dosimeter is necessary and is the responsibility of the person wearing the device

Placement of Personal Dosimeters

• With no protective apron: During routine radiographic procedures dosimeter should be attached to the clothing on the front of the body at collar level to approximate the location of maximal radiation dose to thyroid, head and neck

• With a protective apron: During fluoro, surgery, and special radiographic procedures the dosimeter should be worn outside the apron at collar level on the anterior surface of the body

  • A dosimeter reading that is within acceptable limits outside of the apron ensures a minimal reading under the apron

• Second Monitor

  • Embryo-fetus monitors are worn to monitor radiation dose to the abdomen during gestation

  • Extremity dosimeter ring used when performing fluoro procedure that require hands near primary beam or when handling high dose radiation

• A record of radiation exposure should be part of the employment record of all radiation workers

Personal Monitoring Devices Currently Available

• Optically stimulated luminescence (OSL) Dosimeter

• Extremity dosimeter (thermoluminescent dosimeter (TLD) ring)

• Thermoluminescent dosimeter (TLD)

• Pocket ionization chamber (pocket dosimeter)

• Personnel digital ionization dosimeter

Optically Stimulated Luminescence Dosimeter (OSL)

• Most common type used for monitoring occupational exposure

• Contains an aluminum oxide detector

• Can be worn for up to 1 year but is common practice to wear it for 1-3 months

• Has three separate filters inside

  • Aluminum

  • Tin

  • Copper

• Is the second most sensitive out of the devices

• A control monitor is sent with each batch of OSLs to monitor any radiation during transit

• Light weight and durable

• Disadvantage is that occupational exposure is recorded only in area where device is worn

• Monitoring services supply personnel monitoring reports follows you from employer to employer

• When M appears under the current monitoring period or in the cumulative columns, it signifies that an equivalent dose below the minimum measurable radiation quantity was recorded during that time

Extremity Dosimeter Thermoluminescent Dosimeter (TLD) Ring

• Know as an extremity dosimeter

• May be used as a second monitor during fluoro that require hands need the primary beam

• Reusable

• Used in Nuc Med

• TLD element is protected by nengraved cover

Thermoluminescent Dosimeter (TLD)

• Contains a crystalline form (powder or, more frequently, small chips) of lithium fluoride (LiF), which functions as the sensing material of the TLD

• May be used for up to 3 months

• Humidity, pressure, and normal temperature changes do not affect the TLD

• Disadvantage is its high cost and can be read only once

• A graphical plot known as a glow curve represents a unique signature of the exposure received by the TLD dosimeter

• A device called a TLD analyzer measures the amount of ionizing radiation to which a TLD badge has been exposed

Pocket Ionization Chamber

• Most sensitive type of personnel dosimeter

• Not commonly used in diagnostic imaging

• Resembles an ordinary fountain pen, but it contains a slender cylindrical (thimble) ionization chamber that measures radiation exposure

• Two Types:

  • Self-reading- has a built in electrometer

  • Non-self-reading-requires a special accessory electrometer

• Contains two electrodes

  • One positively charged - Central electrode

  • One negatively charged - outer electrode

• A special charging unit is required, can discharge if they are subjected to mechanical shock, which would result in a false high reading

• Used to provide immediate exposure readouts for radiation workers who worked in high exposure areas

• Compact, easy to carry, reasonably accurate and sensitive, and convenient to use

• Disadvantage is there are $150 or more per unit

Personnel Digital Ionization Dosimeter

• Fairly new device

• Provides radiation workers with an immediate measurement of radiation exposure when connected to a computer via USB

• Long-term exposure tracking

• Small in size, light weight, durable

• Appearance is similar to a flash drive

Radiation Survey Instruments for Area Monitoring

• Three different gas filled radiation detectors serve as field instruments

  • Ionization chamber type survey meter (Cutie pie)

  • Proportional counter

  • GM survey meter

• All three detect the presence of radiation and when properly calibrated give a reasonably accurate measurement

• They each have their own special use and they are not all equally sensitive in the detection of ionizing radiation

Ionization Chamber Type Survey Meter “cutie pie”

• Is both a rate meter device (for exposure rate) used for area surveys and an accurate integrating or cumulative exposure instrument

• Is useful for monitoring radiographic x ray installations when exposure times of a second or more are chosen and for measuring fluoro and CT scatter radiation exposure rates at a second or more

• Advantage: Measures wide range of radiation exposures within seconds

• Disadvantage: Has a delicate detector

Proportional Counter

• No useful purpose in diagnostic imaging

• Used in lab setting to detect alpha and beta radiation and small amounts of other types of low level radioactive contamination

Geiger Muller (GM) Survey Meter

• The most common of these is a geiger muller (GM) survey meter

  • Portable

  • Monitors Nuc Med Facilities

  • Detects areas contaminated by radioactive materials

  • Allows rapid monitoring

  • Can be used to locate a lost radioactive source or low level radioactive contamination