Radiation Biology

What sparks a chemical change within cells and causes?

Biological damage

When does x-rays become dangerous

When damage occurs to important molecules, such as DNA

Sequence of radiation injury

X-ray photons interact with cells, causing ionization, excitation, and the breaking of chemical bonds. This leads to chemical changes and eventually biological changes

What is the most common form of radiation injury

Free Radical

Free radical is…

An atom with a single electron and its outermost shell is unstable

Free radical formation occurs when…

a photon ionizes water and the h20 molecules are broken into ions

Radiation injury: Free radical formation

X-ray photons interact with water in cells then ionization occurs, then resulting in free radical formation

Radiation causes biological damage two different ways:  ionization and/or free radical formation.

True

 A free radical is a stable atom that often donates electrons to unstable atoms.

False

When water is ionized, free radicals form, and hydrogen peroxide may be produced. 

True

Free radical formation is an uncommon occurrence and causes only a few rare diseases/illnesses. 

False

Direct theory:

Radiation photons directly hit a sensitive part of a cell and damages it

Indirect theory

Free radiation formation damages to DNA, cell structures, and proteins

Which is more likely to occur? Direct or indirect theory?

Indirect

Linear:

as dose goes up, damage goes up

Non-threshold

There is no amount of dose that does not result in any damage

Linear Nonthreshold or Threshold

Linear threshold

Linear Nonthreshold or Threshold

Threshold

Which one happens in dental radiation, Linear nonthreshold or threshold

Linear Nonthreshold

What are stochastic radiation effects?

Effects that can occur at any dose without a threshold.

Does the severity of stochastic effects depend on the radiation dose?

No, but the probability increases with increased exposure.

What are examples of stochastic effects?

Cancer and genetic mutations.

Can stochastic effects be somatic or genetic?

Yes, both.

What are non-stochastic radiation effects?

Effects that occur only after a high-dose threshold is reached.

How does radiation dose affect the severity of non-stochastic effects?

Severity increases as the dose increases.

What are examples of non-stochastic effects?

Erythema, hair loss, and cataract formation.

Are non-stochastic effects somatic or genetic?

Somatic only.

What are the three stages in the sequence of radiation injury?

Latent period, period of injury, and recovery period.

What is the latent period?

The time between radiation exposure and observable effects.

What happens during the period of injury?

Cell death, abnormal mitosis, giant cell formation, and chromosomal changes.

What happens during the recovery period?

Cells begin repairing themselves after radiation exposure.

Is all radiation injury permanent?

No, low-level radiation injury is highly repairable.

What is the cumulative effect of radiation?

Non-repairable radiation damage accumulates in tissues over time.

What can cumulative radiation damage cause?

Cancer, cataracts, and genetic mutations.

What five factors determine radiation injury?

Total dose, dose rate, amount of tissue irradiated, cell sensitivity, and age.

How does total dose affect radiation injury?

Higher total dose causes greater risk of damage.

How does dose rate affect radiation injury?

Higher dose rates cause greater damage because repair cannot take place.

How does the amount of tissue irradiated affect radiation injury?

Larger exposed areas increase the risk of damage.

Which cells are most sensitive to radiation?

Young and rapidly dividing cells.

How does age affect radiation sensitivity?

Children are more susceptible to radiation damage.

What are short-term radiation effects?

Effects caused by high amounts of radiation absorbed in a short time.

What are examples of short-term radiation effects?

Nausea, vomiting, and hair loss.

Are short-term radiation effects reversible?

Yes.

What are long-term radiation effects?

Effects caused by low amounts of radiation exposure over many years.

What are examples of long-term radiation effects?

Cancer, birth defects, and genetic mutations.

Are long-term radiation effects reversible?

No.

What are genetic radiation effects?

Effects that occur in reproductive cells and affect offspring.

Do genetic effects affect the exposed person's health?

No, they affect the health of their offspring.

Are genetic effects repairable?

No.

What are somatic radiation effects?

Effects that occur in all cells except reproductive cells.

What are examples of somatic effects?

Cancer, cataracts, and leukemia.

Are somatic effects repairable?

Sometimes.

What does radiosensitive mean?

Cells or tissues that are highly sensitive to radiation.

What does radioresistant mean?

Cells or tissues that are less sensitive to radiation.

What three factors determine cellular sensitivity to radiation?

Mitotic activity, cell differentiation, and cell metabolism.

How does mitotic activity affect radiation sensitivity?

Cells that divide frequently are more sensitive.

How does cell differentiation affect radiation sensitivity?

Immature or unspecialized cells are more sensitive.

How does cell metabolism affect radiation sensitivity?

Cells with higher metabolism are more sensitive.

Which organs are radiosensitive?

Lymph nodes, bone marrow, testes, and intestines.

What are the four critical organs in dental radiology?

Skin, thyroid gland, eye lens, and bone marrow.

Why are these organs considered critical in dental radiology?

They are important organs that are frequently exposed during dental imaging.

What are the two radiation measurement systems?

Traditional (standard) system and SI system.

What is radiation exposure?

The amount of ionization produced in air by x-rays.

What is the traditional unit for exposure?

Roentgen (R).

What is the SI unit for exposure?

Coulombs per kilogram (C/kg).

How many C/kg equal 1 roentgen?

2.58 × 10⁻⁴ C/kg.

How many roentgens equal 1 C/kg?

3.88 × 10³ R.

What is radiation dose?

The amount of radiation energy absorbed by tissue.

What is the traditional unit for absorbed dose?

Radiation absorbed dose (rad).

What is the SI unit for absorbed dose?

Gray (Gy).

How many grays equal 1 rad?

0.01 Gy.

How many rads equal 1 gray?

100 rads.

What is dose equivalent?

A measurement used to compare the biological effects of different types of radiation.

What is the traditional unit for dose equivalent?

Roentgen equivalent in man (rem).

What is the SI unit for dose equivalent?

Sievert (Sv).

How many sieverts equal 1 rem?

0.01 Sv.

How many rem equal 1 sievert?

100 rem.

What is the formula for dose equivalent in the traditional system?

rem = rad × QF.

What does QF stand for?

Quality factor.

What does the quality factor indicate?

How dangerous a type of radiation is.

What is the quality factor for x-rays?

1.

What is the difference between exposure, dose, and dose equivalent?

Exposure measures radiation in air, dose measures energy absorbed by tissue, and dose equivalent measures biological effects.

What is radiation risk?

The likelihood of adverse effects from radiation exposure.

According to the lecture, what is the estimated risk of fatal cancer from dental x-rays?

3 in 1 million.

Which tissues are at higher risk during dental radiography?

Thyroid gland, bone marrow, skin, and eyes.

What can radiation damage to bone marrow cause?

Leukemia.

What can radiation damage to the eye lens cause?

Cataracts.

What can radiation exposure to the skin cause?

Erythema (reddening).

What four precautions help limit patient radiation exposure?

Film speed, collimation, proper technique, and exposure settings.

How does higher kVp affect skin dose?

Higher kVp reduces skin dose.

How does collimation reduce radiation exposure?

It limits the area exposed to the x-ray beam.

How does proper technique reduce radiation exposure?

It helps prevent unnecessary retakes.

According to the lecture, how many dental x-rays equal approximately one chest x-ray?

100 dental x-rays.

What are the two mechanisms of radiation injury?

Ionization and free radical formation.

What does a dose-response curve demonstrate?

The relationship between radiation dose and tissue damage.

What type of dose-response relationship applies to dental radiation?

Linear, non-threshold.

What does linear, non-threshold mean?

As radiation dose increases, damage increases, and no completely safe threshold exists.

What determines the amount of radiation exposure a patient receives during dental imaging?

Receptor, collimation, and technique.

When should dental radiographs be prescribed?

When the benefit of detecting disease outweighs the risk of radiation damage.

Why is minimizing dental radiation exposure important?

All ionizing radiation can produce biological changes in living tissue.