Radiation Biology Reading: Chapter 4

Radiation Biology is the study of the effects of radiation on living tissue.

X-rays are a form of ionizing radiation. When x-rays strike patient tissues, ionization results.

All ionizing radiations are capable of producing biologic changes in living tissue.

Radiation Biology

Effects of Ionization

ATOMSwhich may affect

MOLECULESwhich may affect

CELLSwhich may affect TISSUES

which may affect ORGANS

which may affect THE WHOLE BODY

Radiation Causes Ionization of:

Direct Theory◦when radiation interacts with atoms of the DNA molecule, it may affect the ability of a cell to reproduce and survive.

◦Direct injuries from exposure to ionizing radiation occur infrequently.

Theories of Radiation Injury:

Indirect Theory: when x-ray photons are absorbed within the water

inside a cell it can cause the formation of toxic substances. (water to hydrogen peroxide!)

This can ultimately lead to the destruction of the cell.

Injuries of this type occur frequently because our body cells contain so much water. (70 – 80% water!)

Theories of Radiation Injury

Free Radical Formation

So…if ALL ionizing radiation is harmful, what level of exposure is considered “acceptable”?

With radiation exposure, a dose-response curve can be used to correlate the:◦Response (or damage) to the tissue ◦With the:◦Dose (or amount) of the radiation received

Dose Response Curve

Turn to page 36 in your books. With radiation a “linear non-threshold”

relationship is seen. A LINEAR relationship indicates that the

response of the tissues is DIRECTLY PROPORTIONAL to the dose level.

A non-threshold relationship indicates that a threshold lose level DOES NOT EXIST for radiation.

Dose Response Curve

Threshhold Curve

The Latent Period The Period of Injury The Recovery Period

Sequence of Radiation Injury

The latent period is defined as the time between exposure to x-rays, and the appearance of radiation damage.

This is the first step in the sequence of radiation injury.

The Latent Period

The latent period can be short or long depending upon:◦ Total dose of radiation received◦ The amount of time, or rate, it took to receive the

dose. As you may expect:

◦ The MORE radiation received and ◦ The FASTER the dose rate, ◦ The SHORTER the latent period

The Latent Period

A variety of cell injuries may occur.◦ Cell death◦ Changes in cell function◦ Breaking or clumping of chromosomes◦ Formation of giant cells◦ Abnormal cell division or cessation of cell division

The Period Of Injury

Not all cellular radiation injuries are permanent!

Most damage caused by low-level radiation injury is repaired within the body’s cells!!

Scatter Radiation remains in cells, but the body can slough it off in 24-48 hours. However, repeated exposure does not allow the body time to adjust.

The Recovery Period

The effects of radiation exposure are additive, and unrepaired damage accumulates in the tissues.

The cumulative effects of repeated exposure can lead to health problems.◦ Cancer◦ Cataract formation◦ Birth defects

◦ See table 4-1 at the bottom of page 37.

There is a CUMULATIVE EFFECT

Total Dose:◦ Greater damage with larger amounts of radiation

Dose Rate:◦ A high dose rate does not allow time for cellular

damage to be repaired. Amount of tissue radiated:

◦ Total body irradiation produces more adverse effects than if small, localized areas of the body are exposed.

Cell sensitivity Age

Factors Affecting Radiation Injury

Cell sensitivity:◦ More damage occurs in cells that are rapidly

dividing. Age:

◦ Children are more susceptible to radiation damage than adults.

Factors Affecting Radiation Injury

Short Term Effects: high doses of radiation over short periods of time tend to kill cells.◦ Death◦ Skin burns (erythemia), peeling, blistering◦ Hair loss◦ Sterility◦ Cataracts

Long Term Effects: low doses of radiation over extended period of time produce chronic, or long-term effects, which may not be observed for many years.

Short Term and Long Term Effects:

Somatic Effects: Occur in all cells of the body except the

reproductive cells. These changes are not passed along to

future generations. They only affect the individual exposed. Primary consequence is cancer

Somatic and Genetic Effects:

www.ehow.com/video_49847#25537E

Genetic Effects: Occur in reproductive cells Are passed along to future generations These changes do not affect the exposed

individual, but are passed along by mutations in offspring.

Genetic damage cannot be repaired

Somatic and Genetic Effects

Somatic VS Genetic Effects of Radiation

Tissues and organs vary with their sensitivity to radiation.

Radiosensitive organs include:◦ Lymphoid tissue (small lymphocyte)◦ Bone marrow (blood forming tissue)◦ Testes◦ Intestines

Radioresistant organs include:◦ Salivary glands◦ Kidney ◦ liver

Tissue & Organ Sensitivity

A critical organ is an organ that, if damaged, would diminish the quality of a person’s life.

In dentistry, some tissues and organs are designated as critical because they are exposed to more radiation than others during dental radiographic procedures.

Critical Organs

The critical organs exposed during dental radiographic procedures include:◦Skin◦Thyroid gland◦Lens of the eye◦Bone marrow (aka: blood forming tissue)

◦Turn to page 41 of your text

Critical Organs

Critical Organs

Panoramic X-ray Exposure Bite-wing X-ray Exposure

Currently 2 systems are used Traditional/Standard System

◦ Roentgen (R)◦ Radiation absorbed Dose (rad)◦ Roentgen equivalent (in) man (rem)

SI System◦ Coulombs/kilogram (C/kg)◦ Gray (Gy)◦ Sievert (Sv)

Radiation Measurement

Roentgen (R)- ◦ This is the traditional unit of exposure. ◦ That is the amount of ionization created in a given

volume of air.

Exposure Measurement - R

Radiation absorbed dose (rad) This is the traditional unit of dose Dose can be defined as the amount of

energy absorbed by a tissue.

Dose Measurement - RAD

Different types of radiation have different effects on tissue.

The dose equivalent measurement is used to compare the biological effects of different types of radiation

In the traditional system, the unit of dose equivalent is roentgen equivalent (in) man or rem.

Dose Equivalent Measure - REM

Radiation can come from 2 sources:

◦ Natural Background Radiation: this radiation comes from the sun, earth, and atmosphere

◦ Artificial Radiation: (man-made) medical/dental x-rays, nuclear, consumer products

Sources of Radiation

Sources of Radiation

Sources of Radiation

Sources of Radiation

Smoke detectors that use “americium”-241 Lawn fertilizer containing potassium-40Cigarettes Gas lanterns Exit signs Natural gas appliancesBrick or stone housesColor television sets

Consumer Products

Fukashima Nuclear Disaster

www.youtube.com/watch?v=#2553F2

Radiation is harmful to living tissue. Because biological damage results from x-

ray exposure, dental radiographs should be prescribed ONLY WHEN the benefit of disease detection outweighs the risk of biologic damage.

When dental x-rays are properly prescribed and exposed, the benefit far outweighs the risk.

Risk vs. Benefit Principle

Pro and Cons of Dental Radiation Pros Can help to detect:

◦ Caries◦ Cysts◦ Tooth abscess/infection◦ Retained Roots/Foreign

Bodies◦ Periodontal Disease◦ Foreign Bodies◦ Growth Irregularities◦ Tooth Development◦ Tooth impactions

Cons Tissues that can be

effected by radiation:◦ Embryonic tissue◦ Blood and bone marrow◦ Skin◦ Connective tissue◦ Nerve◦ Brain◦ Muscle cells◦ Enamel

The ADA sets guidelines for how frequently patients should have radiographs taken based on many factors.

We will discuss these in the next section of this course on “Radiation Protection”.

Guidelines for Radiation Exposure for Dental Patients