WEEK 8 RADIATION BIOLOGY & PROTECTION PART 2 RADIOLOGIC TECHNOLOGY A 2008 D Charman Contributions by: Kelly Clark, Estella Turner Carlton & Adler, Mosby Publishers, Thompson Publishers Early measurement of Radiation Skin dryness & erythemia Ulcers formed Late Effects: Cataracts Cancers AVE population exposure= 20 30 mrem/year Some natural background in the United States average mrem/yr with the majority due to radon gas, a daughter product of uranium decay. However, many places on earth receive more than 1000 mrem/yr from radon. MEDICAL IMAGING MEDICAL X-RAYS DENTAL X-RAYS GREATEST SOURCES OF MAN-MADE RADIATION UNITS OF RADIATION MEASUREMENT To quantify the amount of radiation a patient or worker receives Conventional (British)Units vs. SI Units Conventional (British) Units Used Since The 1920s A System Of Units Based On Metric Measurements Was Developed By The International Committee For Weights And Measures. SI Units SI Units Were Officially Adopted In 1985 US still using old system in measurement Conv. Units SI Units RADS REMS R - ROENTGEN GRAYS SIEVERT C/KG Not equal in amount Comparsion of Units R - ROENTGENS RADS PATIENT DOSE REMS OCCUPATIONAL EXPOSURE ROENTGEN (R) SI unit = C/KG THE QUANTITY OF X-RADIATION ONLY EXPOSURE IN AIR OUTPUT OF XRAY TUBE DOES NOT INDICATE ACTUAL PATIENT EXPOSURE OR ABSORBTION RADIATION ABSORBED DOSE (RAD) SI = GRAY (Gy) MEASURES THE AMOUNT OF ENERGY ABSORBED IN ANY MEDIUM. (the patient) 1 Gy = 100 rads 1/100 Gy = 1 rad Radiation Equivalent Man DOSE EQUIVALENT Used for employee Traditional Unit = REM SI Unit = Sievert (Sv) 1 Sv = 100 rem RADIATION EQUIVALENT MAN (REMS) SI UNITS = SEIVERT Not all types of radiation produce the same responses in living tissue The unit of dose equivalence, expressed as the product of the absorbed dose in rad (or gray) and quality factor. RAD x QF = REM used for occupational exposures can be used when for dose of patient REM / SIEVERT 1 Sv = 100 REM 1/100 SV = 1 REM THE PRODUCT OF THE GRAY x QUALITY FACTOR (QF) RAD x QF Used for occupational exposure EMPLOYEE EXPOSURE RADS REMS RADS GRAYS PATIENT ABSORBED DOSE REMS SIEVERTS Employee (technologists) = Rad VS. Rem 1 RAD X QF = 1 REM 1 GRAY X QF = 1 SIEVERT QF FOR X-RAYS = 1 So Rads = Rems TYPES OF RADIATON (ALL CAUSE IONIZATION) PARTICULATE ALPHA BETA FAST NEUTRONS Unit of mesaure is the curie (Ci) or becquerel (Bq) Very low energy = More destructive ELECTROMAGNETIC XRAY GAMMA (damaged caused by indirect action = free radicals can be repaired) QUALITY FACTOR Qualifies what the damage is from different types of radiation Example: QF for X-ray is 1 QF for alpha is 20 Alpha is 20 x more damaging to tissue Biological Response to Ionizing Radiation X-ray interactions with matter (human tissue) can cause biological changes. Technologists must understand cellular biology and how radiation interacts with cells in order to protect oneself and the patient. Why did the bunny die?? BUNNY A Received 200 rads BUNNY B Received 200 rads Why did the bunny die?? BUNNY A 200 rads x 1 for X-RAY = 200 RADS BUNNY B 200 rads x 20 for alpha = 4000 rads Response of cells to radiation CELL SENSITIVITY TO RADIATION DEPENDANT ON TYPE OF CELL TYPE OF DAMAGE RECEIVED KIND OF RADIATION EXPOSED TO SENSITIVITY TO RADIAITION Which (Male or Female) GONADs are external vs internal Which gender has gonads from birth? Which gender constantly produces new cells? Which GENDER is more sensitive to radiation at birth? Why? Permissible Occupational Dose Annual dose : per NCRP findings 5 Rem/year 50mSv/year (5000 mrem) Cumulative Dose 1 rem x age 10mSv x age PUBLIC EXPOSURE NON MEDICAL EXPOSURE 10 % of Occupational exposure 0.5 rad or 500 mrad or 50mgray Under age 18 and Students 50 % of Occupational exposure 0.1 rem 10 mrem 1mSv Fetus Exposure Radiation exposure is most harmful during the first trimester of pregnancy Embryo-Fetus Exposure limit 0.05 rem or 0.5 mSv PER MONTH 0.5 rem or 5 mSv total gestaion Education and Training Exposures Students must never hold patients during exposures Effective dose limit (Annual) 0.1 rem or 1 mSv (1/50 of Technologists dose) See chart pg 116 FIG. 97 Graph indicates no-threshold versus threshold response to radiation. Elsevier items and derived items 2007, 2003 by Saunders, an imprint of Elsevier Inc. LINEAR RESPONSE TO RADIATION ASSUMES NO PHOTON IS SAFE A.DIAGNOSTIC X-RAY - No Threshold LOW DOSE OVER LONG EXPOSURE B.Early Radiology Exposure Threshold amount needed to see affect CH 9 PG 115 SOMATIC & GENETIC STOCHASTIC VS NON STOCHASTIC A = CHANCEEFFECTS GENETIC Damage, LEUKEMIA, CANCER DIAGNOSTIC RADIOLOGY B - Determined Dose SKIN ERYTHEMA, CATARACTS, STERILITY RAD -MALIGNANCIES Effects from Radiation CELL TYPES BIOLOGIC RESPONSE TO IONIZING RADIATION. CELL STRUCTURE NUCLEUS & CYTOPLASM Most important part of the cell. CHROMOSOMES, WHICH ARE MADE UP OF GENES. (do not need to study other parts of the cell) Cell Type Examples Radiosensitive: Skin cells, small intestine cells, germ cells Resistant cells: Specialized in structure and function, do not undergo repeated mitosis Nerve, muscle & brain cells Example of cell sensitivity Basic Cell Structure Two parts: 1. Nucleus 2. Cytoplasm Nucleus contains chromosomes genetic info (DNA) DNA is at risk when a cell is exposed to ionizing radiation Cytoplasm 80% water Cellular Absorption Direct vs. Indirect Hit Direct Hit Theory: When radiation interacts with DNA. Break in the bases or phosphate bonds Can injure or kill the cell Indirect Hit Theory: Occurs when water molecules are ionized Produces chemical changes injury or cell death Vast majority of cellular damage is from indirect hit. TARGET THEORY Photons hit master molecule DNA = cell dies Or doesnt hit nucleus and just passes through No essential damage Hormoresis repair that can occur when below 5 rads of expsoure Cell bombarded with photons What damage will they cause? Radiolysis poison water theory H 2 O molecules - Ejection of electron = free radical H2 0 2 = hydrogen peroxide HOH + recombine to H 2 O Radiation scatters in all directions By process of RADIOLYSIS GONADS CAN BE AFFECTED EVEN WITH AN INDIRECT EXPOSURE TO AREA Radiosensitivity of Cells Bergonie & Tribondeau (1906) method of classifying a cells response to radiation according to sensitivity. Cells are most sensitive during active division (primitive in structure & function). The Law of Bergonie & Tribondeaux Cells that are most sensitive to radiation Young immature cells Stem Cells Highly dividing (mitotic) cells Highly metabolic RADIOSENSITIVITY OF CELLS Mitotic activity Specific characteristics of the cell (primitive) Structure Function Somatic Cells Perform all the bodys functions. Possess 2 of every gene on two different chromosomes. Divide through the process of mitosis Germ Cells Reproductive cells of an organism. Half the number of chromosomes as the somatic cells. Reproduce through the process of meiosis. Cellular Response to Radiation Die before mitosis Delayed mitosis Failure to divide at normal mitotic rate Total Body Response to Radiation Acute Radiation Syndrome full body exposure given in a few minutes. 3 stages of response: 1. Prodromal Stage: NVD stage (nausea, vomiting, diarrhea) 2. Latent Period: Feels well while undergoing biological changes 3. Manifest Stage: Full effects felt, leads to recovery or death 3 Acute Radiation Syndromes Early Effects Bone marrow syndrome: results in infection, hemorrhage & anemia Gastrointestinal syndrome: results in diarrhea, nausea & vomiting, fever Central nervous syndrome: results in convulsions, coma, & eventual death from increased intracranial pressure. CNS least sensitive in ADULTS MOST sensitive in the FETUS Late Effects of Radiation Somatic Effects: develop in the individual who is exposed Most common: Cataract formation & Carcinogenesis Genetic Effects: develop in future generations as a result of damage to germ cells. PROTECTING THE PATIENT THE PATIENT MUST BE EXPOSED TO IONIZING RADIATION FOR A DIAGNOSTIC IMAGE TO BE PRODUCED. RISK VS. REWARD ALARA AS LOW AS REASONABLY ACHIEVABLE The RADIOGRAPHER has the responsibility of maximizing the quality of the radiograph while minimizing the risk to the patient Cardinal Principles of Protection Triad of Radiation Safety 1. Time 2. Distance 3. Shielding *Apply to the patient & Technologist NCR Nuclear Regulatory Commission Time Distance Shielding And Containment for radioactivity Time The exposure is to be kept as short as possible because the exposure is directly proportional to time. 20 mrem = 2min 10 mrem = 1min Shielding A lead protective shield is placed between the x-ray tube and the individuals exposed absorbing unnecessary radiation Thickness of Lead Shielding LEAD APRONS MUST BE: 0.25 mm of Pb or equivalent GONAD SHIELDS: 0.50 mm of Pb or equivalent Rules for Shielding Patients radiosensitive organs must be shielded whenever the primary beam is within 4 to 5 cm of the reproductive organs. TYPES OF SHEILDING FLAT /CONTACT SHAPED SHADOW Breast Shield Shadow shields SHEILDING TECHNOLOGIST. 25 mm LEAD LEAD APRON, GLOVES THYROID SHIELD, GLASSES PATIENT . 5 mm LEAD GONAD SHEILDING Primary Barriers Stay out of primary beam Proper shielding when holding during an exposure (not a student) INVERSE SQAURE LAW FORMULA Distance Distance from the radiation source should be kept as great as possible Physical Law: - Inverse Square Law Intensity is Spread Out Personnel Monitoring Devices Film Badges Thermoluminescent Dosimeters (TLD) Pocket Dosimeters Optically Stimulated Luminescence (OSL Dosimeters) Ring Dosimeter (Nuclear Medicine Techs) Personnel Monitoring Devices Are not to be worn when you are the patient. The dose is recording your OCCUPATIONAL exposure Monitoring is required when there is the probability that an individual will receive more than 1/10 or 10% of the maximum occupational dose limit. What is the occupational dose limit? Do monitoring devices protect from exposure? Field Survey Instruments Detects the presence of radiation and the intensity of the source Geiger-Mueller counter Review Units of Measurement NCRP/ NRC ALARA DOSE Cumulative Annual Target Theory Direct vs Indirect Cell Somatic vs Genetic Review QF Quality Factor Radiolysis poison water theory The Law of Bergonie & Tribondeaux Radiation Monitoring Personal Field