Radiation Protection RTMR 284 CHAPTER 20 PART II

ROOM SHIELDING Prevents transmission of radiation through the room walls Required for ALL diagnostic and fluoro rooms Protects against primary , secondary, & scatter radiation Thickness depends on: Distance from the sources Workload Use of area on other side of wall Amount of time beam is pointed at the wall

Primary Barrier Primary Radiation: direct, collimated, useful x-ray beam. Typically 1/16th inch of lead What wall is ALLWAYS a primary barrier? If the floor and ceiling are concrete based, no added shielding is needed There needs to be 7’ of upward primary barrier when the x-ray tube is 5-7’ from the wall

Secondary Barrier Secondary Radiation: made up of scatter & leakage radiation Typically 1/32nd inch of lead What area in the room is ALLWAYS a secondary barrier? Glass is room needs 30% lead by weight Leakage radiation regulations Require <100mR/hr at 1 meter

Protective Barrier Considerations Distance: Lead coverage is proportional to distance from primary radiation source Occupancy: Control (<100 mR/wk) vs. Uncontrolled Area (2 mR/wk) Workload: Thickness of barrier is proportional to work load of the room (mA-min/wk) Use: Amount of time x-ray beam will be directed at a barrier. NCRP Primary Barrier factor = ¼ & Secondary factor = 1 (always present) HVL: Amount of shielding required to reduce radiation intensity to half orig. value TVL: Amount of shielding required to reduce radiation intensity to 1/10 the orig. value.

Radiation Detectors Gas-Filled Detectors: collect ions produced by ionizing radiation producing an output signal. Geiger-Muller Counters: best at detecting Beta particles, extra sensitive to low level radiation ~ survey/detection/calibration uses in field Ion Chambers : positive ions created from interaction of air in chamber and radiation interaction leading to a measureable charge to the electrode in the chamber. Used for assment/pt. dose analysis/quality checks. Scintillation Detectors: use crystals that give off light when struck by radiation. Used as detectors in CT scanners and nuc med gamma cameras

Radiation Detectors Gas-Filled Detectors: collect ions produced by ionizing radiation producing an output signal. Geiger-Muller Counters: best at detecting Beta particles, extra sensitive to low level radiation ~ survey/detection/calibration uses in field Ion Chambers : positive ions created from interaction of air in chamber and radiation interaction leading to a measureable charge to the electrode in the chamber. Used for assment/pt. dose analysis/quality checks. Scintillation Detectors: use crystals that give off light when struck by radiation. Used as detectors in CT scanners and nuc med gamma cameras

Personal Monitors Film Badge Dosimeters: film responds to amount of radiation received in relation to the copper, cadmium, and aluminum filter to estimate the energy of incident radiation. Measure exposures ranging from 0.1 mSv (1o mrem) to 20 Sv (2,000 rem) [total body exposure] Keep in cool dry place when not worn at work! Thermoluminescent Dosimeters: uses lithium fluoride crystals that trap radiation energy. Heating to over 100 degrees C release the energy as light to be measured by a PM tube to get values. Can be small in size and used as ring detectors.

Personal Monitors Pocket Dosimeters: most sensitive and consist of a writing pen sized thimble ionization chamber. Uses a charged voltage reading that is set to zero and measured at the end of the day to convert what amount of radiation is detected based on by how much that voltage is lowered in charge. Time consuming and inaccurate at exposures above the set range of the device Optically Stimulated Luminescence: uses crystal forms of aluminum oxide and is based on the electrons that are stimulated by radiation exposure. Light intensity after released by green laser indicated exposure levels. Reports low doses at 1mrad making it most radiosensitive.

Personal Monitors Monitoring period is typically monthly. Badges and TLD’s are sent back to monitoring company to generate reports. Report includes: mrem doses for the period, quarterly totals, YTD, and lifetime totals. As well as deep dose, lens of eye, and lifetime dose equivalents. Must be worn facing outward in the truck of the body and outside protective aprons near the collar during fluoro exams. Placing the badge in the same area during normal conditions each day will provide the most accurate results. Pregnant radiographers get a “baby” badge to be worn on the abdomen under the protective apron to measure the dose to fetus.