lecture4 radiation biology

7/29/2019 Lecture4 Radiation Biology

1/12


2/12

Lecture 4 24-feb-2013

Radiation Biology

Today we will talk about radiation biology. What will happen to our body chemically

and biologically when taking an x-Ray image? Your reference is as usual; Dental

radiography Principles and Techniques 4th

or 3rd

edition chapter 4.

Radiation Injury

When x-rays hit our body, some chemical changes and biological changes will happen

mainly due to ionization and free radical formation.

Mechanisms of Injury

IonizationIonization results from photoelectric absorption or Compton scatter. Photoelectric

absorption occurs when x-ray gives up all its energy to an inner shell electron and

will displace the electron. Compton scatter, when x-ray interact with outer shell

electron and it will cause recoil scattering of electron and scattering the x-ray photonand we will have recoil electron. So, ionization is an atom carrying positive charge

when it loses electron and negative charge when it gets electron. These free

electrons can interact with other atoms causing chemical and biological changes.


3/12

Free radical formationAnother way of damaging cell and usually the process is indirect. What is free radical?

Free radical is uncharged (neutral atom) that exists with a single, unpaired electron.

It is highly reactive and unstable. Free radical usually form when x-ray interactingwith water molecules in our body. Because our body is rich in water, most of

interactions of x-rays will be with water (indirect effect).

So, the radiation damage can be described in two theories; direct theory and

indirect theory.

Theories of Radiation Injury

a. Direct theoryDirect theory is when the x-ray hit the atom/molecule itself, or critical molecule

within the cell. The most sensitive one is DNA because progress in DNA can result in

death of cell. Nucleus is more sensitive than

cytoplasm and DNA is more sensitive than RNA.

b. Indirect TheoryIndirect theory is when x-ray absorbs by water

and free radical formation. Free radical will

then interact with critical molecules causing

biological damage. An indirect injury results

because the free radicals combine and formtoxins (H2O2) which cause cellular dysfunction.

The law of Bergonie and TribondeauThe law says that the most radiosensitive cell are those that have high metabolic rate,

undergo many future mitosis and are the most primitive in differentiation (actively

divide). So usually for young people or when the in uterus are sensitive to radiation.

So, depending on the cell mitotic rate, much future mitosis the more damage willhappen. Most primitive in differentiation are undifferentiated cells not mature cells.


4/12

Mature cells are radio resistant. However this rule of Bergonie and Tribondeau are

not accepted by all the scientists over the world. Because they said with many

mitosis, more problems will be expressed/ can be seen more. So its not necessarily

that it is radiosensitive.

Dose-response curveThe correlation of damage with radiation dose. When we increase the dose

sometimes well increase the damage.

This happens and we call this as

linear (straight line) relationship. Increase

the dose will increase the damage.

Non threshold dose response is

referred to as stochastic effects (doesnt

depend on the dose). No matter how small

is the dose, this can results in damage.

In dentistry, we are mainly dealing with stochastic effect (non threshold). A

nonthreshold relationship indicates that a threshold dose level for damage does not

exist. When we have threshold, we increase the damage above the threshold, thedamage will increase. In case of non threshold/ stochastic effects, when we increase

the dose, well also increase the chance of damage. Stochastic effects do not have a

dose threshold. The effects do not depend on the absorbed dose. Examples of

stochastic effects include cancer induction and genetic mutations.

Examples of nonstochastic effects include erythema, loss of hair, cataract formation,

and decreased fertility.

REMEMBER :1) chance effects : stochastic effects : nonthreshold (not everyone will get

the disease)

2) determined dose : nonstochastic effects : threshold (when reach certain

threshold, everyone exposed will get the disease)


5/12

Sequence of radiation injurySometimes when we give radiation, it will result in damage immediately especially

when the dose is large; this is known as acute radiation syndrome. But sometimes it

takes time for the signs and symptoms to appear especially when the dose is smalland over the time given dose.

Now we have something called latent period. A latent periodcan be defined as time

between getting the dose and seeing the observable clinical signs (manifestations).

Period of injurywill occur after latent period. The last one is recovery period.

Recovery period is when our body is able to correct problems from radiation injury

especially when the dose is small. Some says that damage actually cant be corrected

by our body and this will lead to accumulation of errors this is cumulative effects

irreversible. And this is the most dangerous period effect.

Making small x-rays in dental practice only use low dose. However its still

dangerous due to stochastic effects and also cumulative effects. Many x-rays are

exposed to our body either in low or high dose and we dont know how our body will

deal with this x-rays. Sometimes it can result in damage which cant be repaired

suddenly cancer appears.

Critical organsSome organs in our body are known as critical organs; the most effective bioradiation.

When these organs get damage, this will sacrifice humans life causing major changes

in our life. These critical organs when theyre damaged can result in cataracts, bone

marrow leukemia, salivary gland cancer, thyroid cancer and skin cancer. Critical

organs in our body will diminish humans life when it gets radiation injury.

Determining factors for radiation injuryThe factors that influence radiation injury are:-

a) Total dose: When we increase the total dose, well increase the damage.However, it depends whether it is stochastic or nonstochastic effects.

b) Dose rate: When we give large dose for short period of time this will causedamage. Unlike when we take small doses in long period of time.


6/12

c) Amount of tissue irradiated: Total-body irradiation (large area of the body)produces more adverse effects than if small, localized areas of the body are

exposed.

d) Cell sensitivity: Highly sensitive cells such as rapidly dividing cells and youngcells that undergo mitosis will get more damage.

e) Age: Young kids, children, in uterus are more sensitive to radiation.Radiation effectsRadiation effects can be divided into short term and long term effects, somatic

and genetic effects and effects on cells, tissues and organs.

Short-Term and Long-term effects

Short-term effects - when you receive a large dose in short period of time. Acute

radiation syndrome (ARS) is a short-term effect and includes nausea, vomiting,

diarrhea and hemorrhage.

Long-term effects when small amount of radiation is absorbed repeatedly over a

long period of time. This can be related to cancer and genetic defects.

Info :Short term effects can be seen within minutes, days or weeks

whereas long term effects appears after years, decades or

generations.

Somatic and genetic effects

Somatic cells are all the cells in our body except the reproductive cells (gonads). So

what is somatic and what is a genetic effect?

Somatic effects: When the damage is expressed by the person who got the radiation.

Only the person who got the radiation is affected. Somatic effects of radiation

include cancer and cataracts.

Genetic effects: When the damage is not expressed by the person who got the

radiation but can be seen on offspring. Radiation-induced mutation affects the

health of offspring and the damage cant be repaired.


7/12

So, somatic effects are seen in the person irradiated and genetic effects are not seen

in the person irradiated but are passed on to future generations.

Radiation effects on cells

How about the cells? The cells can be classified into highly sensitive, medium and low

sensitivity to radiation. Nerve and muscles have the least sensitivity (resistant) to

radiation. The highest sensitivity cells to radiation are lymphocyte, bone marrow,

reproductive cells.

Radiosensitive Radioresistant

Lymphocyte Mature bone

Bone marrow Muscle

Reproductive cell nerveImmature bone

Radiation effects on organs

The organs can also be classified into radiosensitive organs and radioresistant organs.

Radiosensitive organs are composed of radiosensitive cells. (Dr Mustafa asks us to

memorize all the organs/cells listed)

Radiosensitive Radioresistant

Lymph tissue Salivary gland

Bone marrow kidney

Intestine liver

Critical organs exposed during dental procedure include the following:

a) Skinb) Thyroid glandc) Lens of the eyed) Bone marrow


8/12

We can also divide

induced cancer. E.g.: s

Radiation measu

Units of measurement

In the past we have tradi

(SI system).

Traditional units ia) Roentgen (R)b) Radiation absorbec) Roentgen equivale

For x-rays, 1R is equal to

The SI units of radia) Coulombs/kilograb) The gray (Gy)c) The sievert(Sv)

Exposure measurement

The measurement of ioni

measured by roentgen (R

as coulombs/kilogram (C

Dose measurement

The absorbed dose, the a

the tissue to the list of tissue suscepti

alivary gland.

ements

ional units but nowadays we use the i

cludes :

dose (rad)

nt (in) man (rem)

1 rad and equal to 1 rem.

tion measurement are :

(C/kg)

zation in air (amount of radiation) pro

). The new measurement equivalent t

kg).

mount of energy absorbed by tissue i

ble to Radiation

nternational system

duced by x-rays is

o roentgen is known

called as rad in


9/12

traditional unit. Rad is radiation absorbed dose. The new SI unit is gray(Gy). The

conversion for rad and Gy can be expressed as follows :

1 rad = 0.01 Gy

1Gy = 100 rads

Dose equivalent measurement

We have something called dose equivalent and effective dose. What is dose

equivalent? And what is effective dose? We use dose equivalent (rem) when we

want to convert the effect between different types of radiation. So now we have

something called as weighing factor/quality factor. Alpha can results more damage

to our body compared to X-rays. Why? Because of dose equivalent measurement,

the weighing factor of alpha is small. We have something call linear energy transfer

(LET); the rate of energy deposition by radiation. Alpha particles, eventhough theyre

slow, they have mass so they will depart more energy, and the rate of energy

deposition in our body is higher than x-ray. Alpha is high linear energy transfer, not

fast like x-rays in general, so will deposit more energy.

The traditional unit of dose equivalent measurement is rem. The SI unit equivalent to

rem is sievert(Sv).

1 rem= 0.01sv

1 Sv = 100rems

So, any form of radiation produce the same radioeffect is known as 1 rad x-ray

radiation. So this is to calculate biologic effect of different rate of radiation.

Another question; what about the effect of radiation dose progress in our

body? Do you thinkthe effect will be the same? No! why? Some parts of our bodyare highly sensitive than other areas. So we have also weighing factor for our body.

Effective dose = biggest equivalent dose x tissue weighing factor. (Unit: Sv)

The greater risk of damage is when we have higher weighing factor. So all these can

be converted between different tissues in our body. This is called effective dose.

Radiation risks

Sources of radiation


10/12

As you know, there are natural sources and man-made/artificial sources. Natural

sources mainly the radon gas which is present from the ground and it will come out

from ground for example and it will go to the lung. So, Radon is the main source of

natural radiation. The man-made radiation especially in the medical field, clinical

field, nuclear medicine, x-ray diagnosis and others. (All can be seen in the pie chart

below). We also have radiation from the stars or from the earth.

Dental radiation usually includes only 1% or less than 1% of the total radiation source.Cosmic radiation originates from stars and sun. Terrestrial radiation occurs naturally

and emitted from materials present in the earth and air (rocks & soil).

Risk Estimates

The potential risk of dental radiography inducing a fatal cancer in an individual is

approximately 3 in 1 million. The risk of a person developing cancer spontaneously is

much higher; 3300 in 1 million. Theyre just numbers (as the doctor said lol)

Patient exposure and dose

Amount of radiation varies. There are many factors controlling the exposure dose in

dentistry. Among them are receptor sensitivities, the technique used, kilovoltage

used and collimation.

a) Receptor sensitivity: F-speed film is the highest speed equals only 50-60% of D-speed film. Using F speed film instead of E speed film reduced additional 20%


11/12

more of absorbed dose. Digital receptors require less radiation almost half the

dose of normal radiation on normal films.

b) Technique used: for extraoral radiation, we used the intensifying screensbecause this will increase the dose. It will change the x-ray collide and the light

will expose effect. Cone beam computed tomography need more x-ray than

intraoral. Cone beam CT is CT machine developed for dental propose. The dose

is less than medical. Cone beam CT is 3D imaging modalities.

c) Exposure factors : The use of higher kilovoltage peak reduce the skin dosed) Collimation: Exposure can be limited by using rectangular collimation. Around

60-70% absorbed dose can be reduced.

ALARAWhat is ALARA? ALARA is As Low As Reasonably Achievable. What does this

mean? This means that you must try your best to decrease the dose as much as

possible. Dental radiograph should be prescribed only when the disease

progression outweights the risk of the damage. So you have to ask yourselves, Will

I make benefits from this x-ray?, if theres no benefits why should I do this x-ray?!

For example occlusal caries, most of the time occlusal caries cant really be seen on

radiograph. So why do u ask patient to take x-ray while you can detect this lesion

clinically? This is not allowed in dental practice, this is not ALARA.Another example, why you ask patient to take cone beam CT to detect endodontic

lesion while you can see it in periapical radiograph? I know clinically that this pulp is

not vital but of course I need radiograph to detect the working length for the dental

treatment. Theres no need to ask the patient to take cone beam CT when

radiograph is enough unless you can get benefits from it. Another one example; TMJ

displacement will not get any benefits neither from cone beam nor from radiograph.Major salivary glands irradiation

When our salivary gland receives radiation, this will result in more viscous secretion.

Parotid gland is the most radiosensitive salivary gland. The effect will depend on the

dose given.

Pediatric radiation


12/12

If radiation precedes the calcification it may destroy the tooth part. However the

eruption is radioresistant. Radiation cause shortening of root formation, abortion

root formation but the teeth still erupt even with abnormal root. It is dose

dependent, like in the case of salivary glands. And patients who had radiation

therapy should avoid taking intraoral radiograph during six months after completing

the treatment, so you should postpone taking any radiograph for such patients for 6

months.

Osteo-radio-necrosis

Necrotic bone: dead bone. Radionecrosis means radiation will lead to necrosis of

bone. This radiation causes damage mainly to the periosteum and the cortical bone.

After radiation, this can lead to necrosis especially when there is infection or

trauma or mechanical damages. There should be another reason other than

radiation to cause the damage. Mandible is more affected than maxilla because of

less vascularity in the mandible. The higher the dose is the higher the risk of getting

radionecrosis (as seen in stochastic effect).

The male was more radiosensitive than the female. The males carried most ofthe radiation induced genetic burden.

The amount of radiation required to double the natural and spontaneousmutation rate is between 20 to 200 rads.

THE END

p/s : Sorry for the super late submission of this script T_T forgive me for any mistakeswritten.

Done by: Aina Amalia

Corrected by Sawsan Jwaied

Thanx Aina for your great work

lecture4 radiation biology

Documents