Radiation Monitoring PDF

Chapter 5 Radiation Monitoring Personnel Monitoring MPD = maximum permissible Dose got replaced 1991...

Chapter 5 Radiation Monitoring Personnel Monitoring MPD = maximum permissible Dose got replaced 1991 by EFD in  Requirement for personnel monitoring  Personnel dosimetry—the monitoring of equivalent dose to any person occupationally exposed on a regular basis to ionizing radiation.  Ensure that occupational radiation exposure levels are kept well below annual effective dose (EfD) limits  Create awareness of various radiation exposure monitoring devices and their functions Personnel Monitoring  Required whenever radiation workers are likely to risk receiving 10% or more of the annual occupational EfD limit of 50 mSv (5 rem) in any single year as a consequence of their work-related activities  In keeping with the as low as reasonably achievable (ALARA) concept, most health care facilities issue dosimetry devices when personnel could receive approximately 1% of their annual occupational EfD limit in any month, or approximately 0.05 mSv (50 mrem). Purpose of Personnel Dosimeter  Provides an indication of the working habits and working conditions of diagnostic imaging personnel  Determines occupational exposure by detecting and measuring the quantity of ionizing radiation to which the dosimeter has been exposed over a period of time  Does not protect the wearer from exposure; only capable of detecting and measuring ionizing radiation Measures for dosimeter shallow tissue Deep Tissue lens of the eye  Placement of Personnel Dosimeter  During routine computed radiography, digital radiography, or conventional radiographic procedures  When a protective apron is not being worn, primary personnel dosimeter should be attached to the clothing on the front of the body at collar level.  When a protective apron is used, dosimeter should be worn outside the apron at collar level on the anterior surface of the body. Personnel Monitoring Devices Currently Available Nuc Med Placement of Personnel Dosimeter as a Second Monitor  When a protective apron is worn, the first, or primary, dosimeter is to be worn outside the protective apparel at collar level.  The second dosimeter should be worn beneath a wraparound-style lead apron at waist level. Placement of a Personnel Dosimeter as a Monitor for the Embryo–Fetus  For pregnant diagnostic imaging personnel  Primary dosimeter is worn at collar level.  Second monitoring device is worn at abdominal level. 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.  Purpose of the extremity dosimeter  Laser-etched cover contains identification  Reusable TLD element of the dosimeter onin worn for 3 months 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  TLD = Reusable Personnel Dosimeters  Characteristics  Lightweight and easy to carry  Made of materials durable enough to tolerate normal daily use  Able to detect and record both small and large exposures in a consistent and reliable manner  Outside influences should not affect performance of the instrument  Should be reasonably inexpensive to purchase and maintain  Permit health care facilities to use large numbers of monitors in a cost-effective manner  Types  Optically Stimulated Luminescence Dosimeter (OSL)  Direct Ion Storage (DIS)  standard 3 months Copper Industry = but can be worn Tin for a year Aluminum Optically Stimulated Luminescence Dosimeter (OSL)  Most common type of devise used for monitoring of occupational exposure in diagnostic imaging and radiation therapy.  Contains an aluminum oxide detector. will and create glow glow a curve  Energy discrimination: filters made of aluminum, tin and copper  Sensitivity: accurate reading as low as 10µSv  Control monitor  There is a permanent record Cheapest Optically Stimulated Luminescence Dosimeter (OSL)  Advantages  Lightweight, durable, easily worn  Preloaded packet  Allows for reanalysis  Disadvantages  Occupational exposure is recorded only in the body area where the devise is attached.  Exposure cannot be immediately determined  Optically Stimulated Luminescence Dosimeter (OSL)  Personnel monitoring report  State and federal regulations  See Fig. 5.4A & B  Change in employment by radiation worker  Expensive Reusable Most sensitive 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 TLD is the most accurate and is closely resembles human tissue No Radiation Survey Instruments for Area Monitoring  Three categories  Those without a readout scale  Those with a readout scale  Ionization-chamber based  Most common have a Geiger-Műller tube as their detector  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  Gas-filled detectors include:  Ionization chamber-type survey meter (cutie pie)  Proportional counter  GM survey meter Requirements 1. Portable 2. Durable 3. Reliable 4. Interacts with radiation as tissue does 5. Detects all common types of ionizing radiation 6. Energy of the radiation should not affect the response of the detector 7. Cost effective 8. Calibrated annually to ensure accurate operation Gas-Filled Radiation Survey Instruments  Ionization chamber-type survey meter (cutie pie)  Sensitivity ranges and uses  Advantages and disadvantages  Proportional Counter  Geiger-Műller Survey Meter  Sensitivity and use  Components  Disadvantages  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. Instruments Used to Measure X-ray Exposure in Radiology  Medical physicists use ionization chambers connected to electrometers to perform standard measurements required by state, federal, and health accreditation organizations for radiographic and fluoroscopic devices.