biological effects of radiation
TRANSCRIPT
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 at populations that were accidentally or otherwise exposed. Radiation exposed populations include:
Early X-ray workersRadium Dial PaintersHiroshima and Nagasaki SurvivorsUranium Mine WorkersAnkalosing SpondilitisRingwormAccidents
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 the Biological Damage Process
Damage can be broken down to three distinct time frames:
Physical
Chemical
Biological
Biological DamagePhysical Stage
• Radiation deposits energy
• Excess energy removes an electron from an atom (ionized)
• Very quick! ~10-12 s
Biological DamagePhysical Stage - Ionization
Charge = 0 Charge = +1 (ion)
Biological DamageChemical 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
DNA
Biological DamageChemical Stage
Biological DamageBiological 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 DamageBiological Stage
Several 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!
DNA Replication
Biological Damage“The Big Picture”
All of these cell effects revolve around cell division.
Cells which do not divide will be resistant to radiation damage!
The rapidly dividing cells in your body are the most susceptible to radiation damage.
With this in mind, what tissues do you suppose are the most sensitive to radiation?
Acute Radiation Syndromes
Prodromal
Hematopoietic (Blood)
Gastrointestinal
Central Nervous System
A Prodromal reaction indicates a general insult to the body.
Can be psychosomatic, but generally indicates that a person has received a fatal dose (+1000 rem).
Symptoms are usually seen within 30 min.
Symptoms include: • nausea, vomiting, and diarrhea (GI)• fatigue, listlessness, and apathy (CS)
Prodromal Reactions
Hematopoietic Syndrome Blood cells are constantly regenerating in your body. They have a lifetime of approximately 30 days.
The two cell types which are particularly important: - Platelets (clotting function)
- White Blood Cells (immune function)
This syndrome is observed at doses between 300 and 800 rads.
Hematopoietic SyndromeExample
Gastrointestinal Syndrome
Cells which compose the lining (epithelial) of the intestine are susceptible to radiation damage because they are constantly dividing.
This syndrome only observed at +800 rads.
Before Chernobyl, there was only one documented case.
Gastrointestinal SyndromeIntestinal Epithelial Lining
Central Nervous System Syndrome
The 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 SpeciesLeast
Sensitive
Acute Dose (rad)
Microorganisms
Invertebrates
Plants
Fish
Amphibians
Birds
Mammals
Humans
10 100 1,000 10,000 100,000 1,000,000
MostSensitive
Partial Body Irradiation Effects
TestiesTemporary sterility 15 radsPermanent sterility 500 rads
OvariesSterility 500 rads
Lens Detectable opacities 100 radsCataracts 500 rads
SkinReddening 600 radsBlisters 1000 radsPermanent hair loss 2000 rads
Problems Determining Cancer 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
Control Exposed ExcessTotal Subjects Subjects Cancers
Number of subjects 75,991 34,272 41,719Leukemia 202 58 144 80
All cancers except leukemia 5,734 2,443 3,291 260Stomach 2,007 854 1,153 73
Colon 232 103 129 19Lung 638 253 385 44
Breast 155 57 98 22Urinary tract 133 49 84 19
Myeloma 36 13 23 7
Current Data from Atomic Bomb Survivors
Cancer Risk DataP
oten
tial
Dam
age
to H
ealt
h
Linear H
ypothesis
1 rem 10 rem
Area of controversy
Real data
Dose
Thres
hold
Hypoth
esis
Cancer Risk Coefficients
30Fatal
Cancers
100Unexposed
People
25Fatal
Cancers
100Exposed People
5% Risk of Fatal Cancer
Cancer Risk Coefficients
Based 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 of developing 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 Doses
Medical 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 Measured
Risk = (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 Risk
Risk = (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 Risks
Deaths/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 Risks
Deaths/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 Risks
Deaths/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 1/1,000,000Information taken from Physics and Society,
Vol. 19, No. 4, 1990
ActivitySmoking 1.4 cigarettesDrinking 0.5 l of wine
Spending 1 hr in a coal mineSpending 3 hr in a coal mineLiving 2 days in New YorkTraveling 6 min by canoe
Traveling 10 miles by bicycleTraveling 30 miles by carFlying 1000 miles by jetFlying 6000 miles by jet
ResultCancer, heart disease
Cirrhosis of liverBlack lung disease
AccidentAir pollution
AccidentAccidentAccidentAccident
Cancer from cosmic rays
Risks Which Increase the Chance of Death by 1/1,000,000Information taken from Physics and Society,
Vol. 19, No. 4, 1990
ActivityLiving 2 months in Denver
Living 2 months if stone bldgChest X-ray taken in good hospital
Living 2 months with a smokerEating 40 tblspns of peanut butter
Drinking Miami drinking water for 1 yrDrinking 30 12 oz. Cans of diet soda
Living 5 yrs at site boundary of nuc. plant
ResultCancer from cosmic radiationCancer from natural radiation
Cancer from radiationCancer and heart disease
Liver cancer from aflotoxin BCancer from chloroformCancer from saccharinCancer from radiation
Comparing the Risk
Comparing the Risk
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