Radiation Safety OR: NO SUBTITLE CAN TOP THAT PICTURE Chris Ober, DVM, PhD, DACVR 15 February 2011 Brief History & Terminology Radiation Sources Radiation Effects Decreasing Radiation Monitoring Radiation Chapter I Dr. Wilhelm Konrad Roentgen A Brief History of Radiation Protection 1895: Discovered x-rays 1896: First reports associate x-ray exposure to skin burns & eye damage 1902: First report of skin cancer due to radiation exposure Ionizing Radiation 1907: First use of photographic plate for monitoring of radiation exposure Radiation with enough energy to remove bound electrons from atoms Many types X- and gamma rays Beta particles Alpha particles Can interact with molecules in cells
Radiation Units ionization in air Roentgen (R) Coulomb / kg (C/kg) Absorbed Dose Radiation Absorbed Dose (rad) Gray (Gy) = 100 rad Radiation Units Radiation Dose Equivalent Absorbed dose x Weighting factor Weighting factor for x-rays = 1 Protons = 5, Alpha particles = 20 Radiation Equivalent Man (rem) Sievert (Sv) = 100 rem Chapter II Roentgen Rad, Rem Brief History & Terminology Radiation Sources Radiation Effects Decreasing Radiation Monitoring Radiation Background Radiation: 82% of annual dose Man-made sources (mostly medical): 18% of annual dose Radiation Sources Radiation from space Increased dose at: Poles High altitudes 26 mrem / year Cosmic Radiation Total annual dose: ~360 mrem (15-2500 mrem)
Earth s Crust Radon Uranium Thorium Radon Largest part of background radiation 100-500 mrem / year Enters through basements Internal Ingested radioactive material Minimal amounts 40 K is most important Man-Made Sources Medical radiography Nuclear medicine procedures TV, nuclear fallout, luminous watches Entrance Skin Dose Guidance Levels Radiographs Chest 10 mrem Lumbar Spine 150 Lower GI 800 CT Abdomen 800 mrem Thorax 700 Interventional Coronary Stent 1500 mrem Brief History & Terminology Radiation Sources Radiation Effects Decreasing Radiation Monitoring Radiation Chapter III
Interactions of Radiation with Matter Results of Interactions Damage repaired (NGS) Cell remains viable, but modified (mutation) Cell viable, but unable to multiply (chronic tissue damage) Cell death (acute tissue damage) Effects of Radiation Rate of exposure Amount of body exposed Cell sensitivity Rate of Large dose all at once may result in death Same overall dose divided over a long period of time may not lead to any detectable effects Small insults can be repaired by the body Amount of Body Exposed Large whole-body dose may be fatal Same dose applied to single region in several fractions leads to only local effects Principle behind radiation therapy Cell Sensitivity Most sensitive: rapidly dividing or undifferentiated cells Gonads GI tract Bone marrow Thyroid gland Less sensitive Extremities
Hazards of Radiation Acute Effects Long-Term Effects Genetic Effects Fetal Effects Acute Effects Large Whole Body Doses 3+ Sv (300+ rem) Note the lack of the milli- prefix Pattern of effects Hematological (1+ Sv) GI (10+ Sv) Neurovascular (50+ Sv) Death in weeks to hours Acute Effects Local Injury Rapidly proliferating tissues Skin Mucous membranes GI tract Bone marrow May cause: Moist desquamation Mucositis Can be reversible Acute Effects Local Injury Not a concern in diagnostic imaging Definite concern in radiation Tx Definite concern in interventional radiology This patient: 10hr procedure with estimated local 15-20 Gy dose (required plastic surgery) Balter, et al. Radiology 254 (2010): 326-341 Long-Term Effects Radiation-induced Carcinogenesis Chronic effects in slowly (or non-) proliferating tissues Fibrosis (e.g. lung) Cataracts Cancer is most important effect of low-dose radiation Represents unrepaired damage to DNA cell remains viable, but mutated Cancer is damage to somatic cells, not germ cells Long latent period NO safety threshold, though probability of cancer increases with dose Risk must be extrapolated from higher exposures
Radiation-induced Carcinogenesis Common neoplasms Leukemia Lung Bone Breast Thyroid Skin Low-dose radiation is a weak carcinogen Genetic Effects Mutations in germ cells induced by radiation can be passed on to offspring Radiation does not produce abnormal mutations, just increases the probability of naturally occurring mutations Typical occupational and diagnostic exposures are not thought to lead to significant genetic risk Another Division Fetal Effects Stochastic Probability increases with dose; severity of disease does NOT change No threshold Theoretically it only takes 1 photon to do the necessary damage Examples: Oncogenesis Genetic effects Deterministic Severity increases with increasing dose Like sunburn Dose below a certain threshold will NOT produce effect Common in Radiation Tx Examples: Erythema Cataracts Fetal Effects Human Stage of Gestation Depend on: Dose Dose rate Gestational age Less than 10 days: Fetal death OR No effect Anytime after this Childhood leukemia 10 days-6 weeks: Organ abnormalities Intrauterine growth retardation 6-20 weeks: Permanent growth retardation Microcephaly Mental retardation 25+ weeks: No gross structural abnormalities
Brief History & Terminology Radiation Sources Radiation Effects Decreasing Radiation Monitoring Radiation Chapter IV Veterinary Radiation Manual restraint of patients Sources of radiation Primary beam Scatter radiation Leakage from x-ray tube Radiation Regulations Set by the National Council on Radiation Protection ALARA: As Low As Reasonably Achievable There is NO THRESHOLD for possible damage Occupational Limits Must be at least 18 years old Whole body dose: 5 rem / year Hands / feet: 50 rem / year Specific organ: 50 rem / year Lens: 15 rem / year Fetus: 50 mrem / month Veterinary Staff Mean: < 5 microsv per radiograph < 500 microrem Thus > 10,000 radiographs to reach limit 95% of cases < 2 microsv per radiograph Berl Munch Tierarztl Wochenschr. 2008 May-Jun;121(5-6):228-38. [Radiation exposure of the staff during standardised radiography of dogs and cats] Limiting Radiation Decrease exposure time Increase distance Body shielding But there s no reason to even approach the limit ALARA ALARA ALARA
Limit Time Not referring to the time component of mas Refers to the amount of time personnel are exposed to radiation Limit Time Sedate / Anesthetize patients Technique chart Accurate measurements Faster film-screen combinations Rotate individuals for holding patients Increase Distance Inverse Square Law: Amount of radiation decreases by the square of the distance Doubling the distance reduces the radiation dose to ¼ original dose Increase Distance Use sandbags & tape to minimize manual restraint Increase Distance Increase Distance Do not hand-hold the x-ray tube Use an x-ray tube stand Use cassette holders to keep hands away from beam Even leaning away will help
Increase Distance Collimate the field to only the area of interest Keeps the holder out of the primary beam Decreases scatter radiation
Increase Distance But sometimes a human body accidentally strays into the primary beam If the radiograph is diagnostic, DON T repeat it We re trying to decrease exposure, not double it Direct Body Shielding Lead Aprons Lead Gloves Thyroid Shields Lead Glasses Direct Body Shielding Only provides protection from scatter Scatter dose reduced to 1/20 Primary beam dose only reduced to 1/2 Radiograph aprons and gloves to check for cracks
Brief History & Terminology Radiation Sources Radiation Effects Decreasing Radiation Monitoring Radiation Chapter V Monitoring Radiation Dose UMN: Monitoring device required if may receive > 10% MPD Number of devices may vary Neck Waist Ring Fetal Piece of film in plastic holder darkens with radiation exposure Inexpensive Not as sensitive for lower doses Falsely darkens with increased heat, humidity Film Badge Piece of film in plastic holder darkens with radiation exposure Inexpensive Not as sensitive for lower doses Falsely darkens with increased heat, humidity Film Badge Immediate readout of exposure Most useful in high radiation areas Dropping them is a bad idea Pocket Dosimeter
Thermoluminescent Dosimeter Better than film badge More accurate More sensitive More reliable Not affected by heat or humidity Reusable Another example of a TLD Used to evaluate exposure to hands Most important in nuclear medicine, fluoroscopy Ring Badge Optically-Stimulated Luminescent Dosimeter Even more sensitive than TLD Same advantages as TLD over film Semi-permanent record What Have We Learned? Radiation comes from many sources Radiation is not scary, but is also not to be trifled with Minimizing risk involves 2 principles: ALARA Not being stupid