Biological Effectsand Risks of Ionizing Radiation
Objectives I WILL :1. Explain the basis of radiation effects.2. Compare radiation risks with other common risks YOU WILL:1. Know the additional cancer risk incurred from exposure to 25 rem.2. Make an informed decision with respect to a personally- acceptable emergency radiation risk.
Sources of InformationWe can’t truly perform controlled experiments so we look atpopulations that were accidentally or otherwise exposed.Radiation exposed populations include: Early X-ray workers Radium Dial Painters Hiroshima and Nagasaki Survivors Uranium Mine Workers Ankalosing Spondilitis Ringworm Accidents
Variation in Biological Effect When you are interested in knowing a relationship between radiation and injury, you would like to know such things as: Radiation Type Radiation Energy Part of Body Irradiated Dose Dose Rate
Stages in theBiological Damage Process Damage can be broken down to three distinct time frames: Physical Chemical Biological
Biological Damage Physical Stage• Radiation deposits energy• Excess energy removes an electron from an atom (ionized)• Very quick! ~10-12 s
Biological Damage Chemical Stage• Ionized water can produce what are called “free radicals”• Radicals can be very reactive chemically• The problem occurs when it reacts with DNA• Ionization of DNA directly can also result in unwanted chemical reactions• Still very quick! ~10-7 s
Biological Damage Biological Stage• Biological change reveals itself when a cell tries to replicate• During replication, the cell reads the DNA• What if the DNA had been damaged?!
Biological Damage Biological StageSeveral things can happen to irradiated cells: 1. Immediate death (not likely) 2. DNA damage could lead too: - death during next division - prevention of division - non-fatal mutation (What?!) 3. No effect!
Biological Damage “The Big Picture”All of these cell effects revolve around cell division.Cells which do not divide will be resistant to radiationdamage!The rapidly dividing cells in your body are the mostsusceptible to radiation damage.With this in mind, what tissues do you suppose are themost sensitive to radiation?
Acute Radiation Syndromes Prodromal Hematopoietic (Blood) Gastrointestinal Central Nervous System
Prodromal ReactionsA Prodromal reaction indicates a general insultto the body.Can be psychosomatic, but generally indicatesthat a person has received a fatal dose (+1000rem).Symptoms are usually seen within 30 min.Symptoms include:• nausea, vomiting, and diarrhea (GI)• fatigue, listlessness, and apathy (CS)
Hematopoietic SyndromeBlood cells are constantly regenerating inyour body. They have a lifetime ofapproximately 30 days.The two cell types which are particularlyimportant: - Platelets (clotting function) - White Blood Cells (immune function)This syndrome is observed at doses between300 and 800 rads.
Gastrointestinal SyndromeCells which compose the lining (epithelial) ofthe intestine are susceptible to radiationdamage because they are constantly dividing.This syndrome only observed at +800 rads.Before Chernobyl, there was only onedocumented case.
Central Nervous System SyndromeThe dose required for this syndrome is VERY high(+5000 rads).Essentially, the nervous system is “shorted out”resulting in loss of various bodily functions.Death occurs within a few days.
Radiosensitivity of Species Most Least Sensitive Sensitive Microorganisms Invertebrates Plants Fish Amphibians Birds Mammals Humans 10 100 1,000 10,000 100,000 1,000,000 Acute Dose (rad)
Problems DeterminingCancer Risk• Why the “uncertainty”? • There are no specific radiation induced cancers. • The number of people needed for such a study would be very large. • There is little specific information on dose. • There is an unlimited list of confounding factors.
Cancer Risk Data Current Data from Atomic Bomb Survivors Control Exposed Excess Total Subjects Subjects Cancers Number of subjects 75,991 34,272 41,719 Leukemia 202 58 144 80All cancers except leukemia 5,734 2,443 3,291 260 Stomach 2,007 854 1,153 73 Colon 232 103 129 19 Lung 638 253 385 44 Breast 155 57 98 22 Urinary tract 133 49 84 19 Myeloma 36 13 23 7
Cancer Risk Data Real dataPotential Damage to Health is th es po is y es H th ar yp o ne Li d H ol sh re Th 1 rem 10 remArea of controversy Dose
Cancer Risk Coefficients 100 100Exposed Unexposed People People 30 25 5% Risk of Fatal Fatal Fatal CancerCancers Cancers
Cancer Risk CoefficientsBased upon the Hiroshima and Nagasaki data,the best estimate for risk is estimated by:(Dose) × (0.0008) = Risk of developing a fatal cancer in your lifetime
Cancer Risk Coefficients Example: 25 rads (25) × (0.0008) = 0.02 This means that I have a 2% chance ofdeveloping a fatal cancer in my lifetime from a 25 rad dose.
So...• Radiation in high doses is definitely not good for you (>200 rads)• Radiation in moderate doses increases your cancer risk (5 - 200 rads)• Radiation at doses near or below background may (<5 rads): do nothing help you (maybe)
What You Typically Get in a Year• Contribution of various radiation sources to total average dose equivalent to persons in the United States (NCRP, 1987).• ~300 mrem
Range of DosesMedical procedures(per procedure) • CT head and body: 110 mrem • Chest X-ray: • ~10-30 mrem • Abdominal X-ray: • ~100 mrem
Radiation Center Dose Info• ALARA• General Public • 0.1 rem per year • 2 mR/hr• 5 rem Occupational• Highest annual doses ~0.5 rem• Typical annual dose <0.1 rem
How Risk is MeasuredRisk = (measure of size of hazard) X (probability of occurrence) Example: 15X106 auto accidents in the US per year with 1 death for every 300 accidents. Risk = (15X106 accidents/yr) X (1/300 deaths/accident) Risk = 50,000 deaths/yr Individual risk = 50,000/250,000,000 = 2X10-4/person/yr
Perceived Risk Vs. Actual RiskRisk = (1000 accidents/yr) X (1 deaths/accident) Risk = 1,000 deaths/yr Risk = (1 accidents/yr) X (1,000 deaths/accident) Risk = 1,000 deaths/yr
Range of Actual RisksDeaths/person-yr Interpretation 10-2 • Disease mortality rate 10-3 • Difficult to find risks of this magnitude • Generally unacceptable level • If it occurs, immediate action taken to reduce it
Range of Actual RisksDeaths/person-yr Interpretation 10-4 • People less inclined to concerted action • People willing to spend money to reduce hazard • Safety slogans show element of fear (e.g., “The life you save may be your own.”)
Range of Actual RisksDeaths/person-yr Interpretation 10-5 • People still recognize and are concerned about these risks • People accept a certain level of inconvenience to avoid risks at this level • Safety slogans have precautionary ring (e.g., “Never swim alone.”, “Keep out of reach of children.”)
Range of Actual RisksDeaths/person-yr Interpretation 10-6 • Not of great concern to the average person • Person is aware of these risks, but feels they will not happen to him • Phrases associated with these hazards have an element of resignation (e.g., “An act of God.”) • Some feel such accidents are partly due to stupidity (e.g., “Everyone knows you shouldn’t stand under a tree during a lightning storm.”)
Risks Which Increase the Chance of Death by 1/1,000,000 Information taken from Physics and Society, Vol. 19, No. 4, 1990 Activity Result Smoking 1.4 cigarettes Cancer, heart disease Drinking 0.5 l of wine Cirrhosis of liverSpending 1 hr in a coal mine Black lung diseaseSpending 3 hr in a coal mine Accident Living 2 days in New York Air pollution Traveling 6 min by canoe AccidentTraveling 10 miles by bicycle Accident Traveling 30 miles by car Accident Flying 1000 miles by jet Accident Flying 6000 miles by jet Cancer from cosmic rays
Risks Which Increase the Chance of Death by 1/1,000,000 Information taken from Physics and Society, Vol. 19, No. 4, 1990 Activity Result Living 2 months in Denver Cancer from cosmic radiation Living 2 months if stone bldg Cancer from natural radiation Chest X-ray taken in good hospital Cancer from radiation Living 2 months with a smoker Cancer and heart disease Eating 40 tblspns of peanut butter Liver cancer from aflotoxin B Drinking Miami drinking water for 1 yr Cancer from chloroform Drinking 30 12 oz. Cans of diet soda Cancer from saccharinLiving 5 yrs at site boundary of nuc. plant Cancer from radiation
Damage done to DNA• DNA is made up of three parts… • Sugar (Ribose) • Base • Phosphate• The information carried in DNA is determined by the order of the bases• Radiation and ions from irradiation can alter the order of the bases, therefore causing mutation or death
Damage done to DNA• When DNA is broken, the hydrogen bonds between the bases are broken• They will then recombine in different orders
Damage Cells• Cells that reproduce the fastest are most effected… • Blood • Skin • Reproductive• Least or last effected are non- reproducing cells… • Brain • Nervous
Damage Cells• There are four types of cell damage… • Somatic • Genetic • Directly • Indirectly• Somatic is when damage appears in the individual exposed• Genetic is when damage appears in offspring
Damage Cells• Direct damage is done by the radiation itself• Indirect damage is done by chemical changes in the cell due to free radicals
Medical Uses• Radiation is used in the medical field… • X-rays • Radiation Therapy • Etc.• X-rays are produced by hitting a tungsten plate with electrons, then used to expose film• Radioisotopes can be given in pill form or as a shot
Medical Uses• The most common radioisotope used in the medical field is Tc – 99• Radioisotopes are chosen first by their half-life and energy• Next, expense and availability• People who administer radioisotopes are called Nuclear Medicine Technologists
Lethal Dose (LD)• The LD is what is required to kill an individual• It is usually listed as LD - % of death - # of days• For example LD – 50 – 30 tells us that that a dose to 50% death rate in 30 days• The change in dose and # of days, changes the death rate
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