Radiation Monitoring Chapter 5: Personnel Monitoring

Radiation Monitoring

• Personnel monitoring is required to ensure that occupational radiation exposure levels are kept well below annual effective dose (EfD) limits.
• It involves monitoring equivalent dose to any person occupationally exposed to ionizing radiation on a regular basis.

Personnel Monitoring Devices

• Required whenever radiation workers are likely to receive 10% or more of the annual occupational EfD limit of 50 mSv (5 rem) in any single year.
• The primary purpose of a personnel dosimeter is to provide an indication of the working habits and working conditions of diagnostic imaging personnel.
• It determines occupational exposure by detecting and measuring the quantity of ionizing radiation.

Placement of Personnel Dosimeter

• When a protective apron is not being worn, the primary personnel dosimeter should be attached to the clothing on the front of the body at collar level.
• When a protective apron is used, the dosimeter should be worn outside the apron at collar level on the anterior surface of the body.

Personnel Monitoring Devices Currently Available

• Nuc Med

Extremity Dosimeter

• A thermoluminescent dosimeter (TLD) ring badge is worn as a second monitor when performing radiographic procedures that require the hands to be near the primary x-ray beam.
• The purpose of the extremity dosimeter is to measure radiation exposure to the hands.

Record of Radiation Exposure

• The record of radiation exposure should be part of the employment record of all radiation workers.
• Values represent the average annual EfD to the whole body.

Characteristics of Personnel Dosimeters

• Personnel dosimeters are lightweight and easy to carry.
• They are made of materials durable enough to tolerate normal daily use.
• They can detect and record both small and large exposures in a consistent and reliable manner.
• Outside influences should not affect the performance of the instrument.
• They should be reasonably inexpensive to purchase and maintain.

Types of Personnel Dosimeters

• Optically Stimulated Luminescence Dosimeter (OSL)
• Direct Ion Storage (DIS)

Optically Stimulated Luminescence Dosimeter (OSL)

• The most common type of device used for monitoring of occupational exposure in diagnostic imaging and radiation therapy.
• Contains an aluminum oxide detector that glows when stimulated by light.
• Energy discrimination: filters made of aluminum, tin, and copper.
• Sensitivity: accurate reading as low as 10µSv.
• Control monitor: there is a permanent record.

Advantages and Disadvantages of OSL

• Advantages: lightweight, durable, easily worn, preloaded packet, allows for reanalysis.
• Disadvantages: occupational exposure is recorded only in the body area where the device is attached, exposure cannot be immediately determined.

Direct Ion Storage Dosimeters

• Small ionization gas-filled dosimeter connected to a solid-state device with electrically erasable programmable read-only memory (EEPROM, or E2PROMs).
• Radiation ionizes the gas in the chamber, and the electric charge will “read out” by introducing a signal.
• Read out through a physical connecting device.
• Advantages: instant access to data, lightweight and durable.
• Disadvantages: must be worn to be accurate.

Radiation Survey Instruments for Area Monitoring

• Three categories: those without a readout scale, those with a readout scale, and ionization-chamber based.
• Most common have a Geiger-Műller tube as their detector.
• The simplest form indicates presence of radiation above background level.
• Do not provide a cumulative exposure reading.

Types of Instruments

• Instruments respond to the charged particles that are produced by the radiation interacting with and ionizing the gas in the detector.
• Measure either the quantity of electrical charge resulting from the ionization of gas or the rate at which the electrical charge is produced.

Requirements for Radiation Survey Instruments

• Portable
• Durable
• Reliable
• Interacts with radiation as tissue does
• Detects all common types of ionizing radiation
• Energy of the radiation should not affect the response of the detector
• Cost-effective
• Calibrated annually to ensure accurate operation.

Gas-Filled Radiation Survey Instruments

• Ionization chamber-type survey meter (cutie pie)
• Proportional counter
• Geiger-Műller survey meter

Instruments Used to Measure X-ray Exposure in Radiology

• Ionization chambers can be used to measure the radiation output from both radiographic and fluoroscopic x-ray equipment.
• A “cutie pie” ionization chamber is also used for radiation protection surveys.
• Both the ionization chamber and the electrometer system must be calibrated periodically to meet state and federal requirements for patient dose evaluation.