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