Everything You Need to Know About Radiation Protection Kelli Haynes, MSRS, RT(R) Program Director & Associate Professor Radiation Protection 45 questions of the 200 will be radiation protection (22.5%) 10 -Biological Aspects of Radiation 15-Minimizing Patient Exposure 11-Personnel Protection 9-Radiation Exposure and Monitoring Biological Aspects of Radiation 10 Questions Cell Radiosensitivity Cells and tissues vary in their degree of radiosensitivity Immature cells are nonspecializedrapid cell division Mature cells are specialized-divide slower if at all DNA-most radiosensitive part of cell High Lymphocytes Spermatogonia Erythroblasts Intestinal crypt cells Low Muscle cells Nerve cells Chondrocytes Dose Response Relationships Graphic representation of the relationship between the amount of radiation absorbed (dose) and the amount of damage (response) Linear or nonlinear Threshold or nonthreshold Linear Threshold Dose Dose Linear NonThreshold Response Response NonLinear Threshold Dose Dose NonLinear Nonthreshold Response Response Relative Tissue Radiosensitivities LET RBE OER Linear Energy Transfer (LET) Photons deposit or transfer energy as they travel The average energy deposited per unit of path length Assesses potential tissue and organ damage LET High-LET Radiation Alpha particles Beta particles Low-LET Radiation Gamma rays X-rays Relative Biologic Effectiveness Measures biologic effectiveness of radiations having different LET’s Influenced by radiation type, cell or tissue type, physiologic condition, and biologic result Oxygen Enhancement Ratio Response to radiation is greater when irradiated in the oxygenated state Radiation dose required to cause response w/o O2 OER= Radiation dose required to cause response w/ O2 Cell Survival and Recovery LD 50/30 Adults-3-4 Gy (300-400 rad) Recovery may occur Somatic Effects Biologic damage sustained by living organisms as a consequence of exposure to ionizing radiation Classified as either early (acute) or late Short-term vs. Long-term Nausea Fatigue Redness of skin Loss of hair Intestinal disorders Fever Blood disorders Shedding skin Cancer Embryologic effects (birth defects) Formation of cataracts Carcinogenesis The production or origin of cancer Experiments have shown that radiation induces cancer Cataractogenesis Cataracts-opacity of the eye lens 2 Gy results in partial or complete vision loss Threshold, nonlinear dose-response relationship Sterility Female sterility based on age of the subject-more radiosensitive when younger Temporary sterility-2 Gray (200rad) Permanent sterility-5 Gray (50 rad) ACUTE RADIATION SYNDROMES Hematopoietic Syndrome Whole-body doses ranging from 1 to 10 Gy (100 to 1000 rad) Reduction of blood cells in circulation results in a loss of the body’s ability to clot blood and fight infection Gastrointestinal Syndrome Appears at a threshold dose of approx. 6 Gy (600 rad) and peaks after a dose of 10 Gy (1000 rad) Without treatment, a dose of 6-10 Gy may cause death in 3-10 days Cerebrovascular Syndrome Doses of 50 Gray (5000rad) Death within 2 hours or up to 2 days Embryonic and Fetal Risks Fetus is very sensitive Fetal radiosensitivity decreases as gestation progresses Genetic Effects GSD-used to assess the impact of gonadal dose Dose equivalent to the reproductive organs that would bring genetic injury to the total population PHOTON INTERACTIONS WITH MATTER Coherent Scattering Photon of low energy interacts with atom. No net energy has been absorbed by the atom. Low-energy photons,1-50 kVp Contributes to fog Compton Scattering • Moderate energy xrays, 60-90 kVp • Interaction with outer shell electron • Electron ejected, Atom is ionized • Photon loses energy and recombines with an atom • Fog and Scatter Compton Scattering FIGURE 2-6 Compton scattering is responsible for most of the scattered radiation produced during a radiologic procedure. (From Radiobiology and radiation protection: Mosby’s radiographic instructional series, St. Louis, 1999, Mosby.) Photoelectric Absorption Most important interaction between x-ray photons and the atoms of the pt’s body for producing useful images Higher energy x-rays (23-150 kVp), more likely to penetrate & not interact Interaction b/t photon and inner shell electron X-ray is absorbed Electron ejected Attenuation Process that decreases the intensity of the beam Refers to both absorption and scatter processes Thickness of body part (mass density) Type of tissue (atomic number) Minimizing Patient Exposure 15 Questions Exposure Factors kVp mAs Shielding Protects gonads when w/i 5 cm of collimated beam Females receive more exposure due to location of organs Types of Shields Flat contact shields Shadow shields Shaped contact shields Clear lead Beam Restriction Purpose-confine useful beam Reduce scatter Types Cones Collimators Filtration Effect on skin and organ exposure Effect on beam energy NCRP Report #102 The useful beam shall be limited to the smallest area practicable and consistent with the objectives of the radiological or fluoroscopic examination. Exposure Reduction Patient positioning AEC Patient Communication ALARA Image Receptors Film-screen systems Intensifying screens Digital Image receptors CR and DR Film speed Image Receptors Digital CT, CR, DR, DF, NM, MR, & US Photons on a detector Electronic image Matrix Patient dose Film Intensifying screens convert photons and expose film Analog image Patient dose Grids As grid ratio increases patient dose increases Increases contrast Absorbs Compton scatter Improves quality Increases patient dose Fluoroscopy Pulsed or Intermittent Exposure factors Positioning Fluoroscopy time Personnel Protection 11 Questions Sources of Radiation Exposure (3) Primary x-ray beam Secondary radiation 1. Scatter 2. Leakage Patient Basic Methods of Protection Protective Devices Protective structural shielding Primary Barriers Secondary Barriers Lead Shields Protective Devices Aprons Gloves Thyroid shields Protective glasses Portable (mobile) units Lead apparel Exposure cord Stand at right angles to the patient Fluoroscopy Protective curtain Bucky slot cover Cumulative timer NCRP Report #102 Fluoroscopy Exposure Rates General Purpose: 10 R per minute Non-image Intensified: 5 R per minute High Level Control: 20 R per minute Exposure Switch Guidelines Switch must be of the dead-man type Radiation Exposure and Monitoring 9 Questions Units of Measurement Quantity SI Traditional Exposure Coulomb/kg roentgen Absorbed dose gray Dose equivalent sievert rad rem Dosimeters Film Badge Economical Parts Monitors x and gamma rays Temperature and humidity can cause fog Pocket Ionization Chambers Most sensitive Must be charged to zero Accurate from 0-200 mR OSL Dosimeter Aluminum oxide detector Optically stimulated luminosity occurs when struck by laser light Accurate reading as low as 1mrem TLD’s Look similar to film badge Lithium fluoride Ionization causes crystal to change NCRP #116 Annual occupational effective dose- 50 mSv (5rem) Public Exposure- 1 mSv Embryo/fetus exposure50 mSv/month Dosimetry records NCRP #160 Typical effective dose per exam; varies from 0.1 mSv for a chest xray to 1.5 for a lumbar spine Interventional- ~3mSv CT- range from 2mSv for a head to 10 mSv for a spine That’s All Folks! www.ARRT.org haynes[email protected] Review Questions What is the most radiosensitive part of the cell? Which is more radiosensitive, immature or mature cells? This is a picture of what? Review Questions What is LET? What is LD 50/30? What is an example of an early somatic effect? Late somatic effect? What is carcinogenesis? Review Questions What is the threshold dose for cataracts? What is the threshold dose for temporary sterility? What is the threshold dose for permanent sterility? What is the threshold dose for cerebrovascular syndrome? Review Questions What is the threshold dose for hematopoietic syndrome? What is the threshold dose for gastrointestinal syndrome? What are some types of shields? What is filtration? What does NCRP Report # 102 state? Review Questions Why do we use a grid? What are the 3 sources of radiation exposure? What is the SI unit of measurement for exposure? What is the SI unit of measurement for absorbed dose? Review Questions What is the traditional unit of measurement for dose equivalent? What is the sensing material in an OSL dosimeter? What is the sensing material in a TLD dosimeter? What does NCRP # 116 state?