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Radiography > Radiation Biology > Flashcards

Radiation Biology Flashcards

1
Q

What are the 2 possible mechanisms of radiation injury?

A
  • ionization

- free radical formation

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2
Q

What is ionization? How is it harmful?

A

The process by which an atom acquires or loses an electron. All ionizing radiations will produce changes in human tissue. When x-rays stick the patient’s tissues:

  • produce through the photoelectric effect or Compton scatter
  • results in formation of a positive atom and dislodged negative electron
  • electron interacts with other atoms within the absorbing tissues causing further ionization or the breaking molecular bonds
  • all of which will cause chemical changes within the cell that results in biological damage
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3
Q

What is a free radical?

A

An uncharged atom or molecule that exists with a single, unpaired electron in its outermost shell. They are highly reactive and unstable (basically just an atom in its natural state)

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4
Q

How are free radicals formed?

A

When an x-ray photon ionizes water, the primary component of living cells

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5
Q

If free radicals recombine?

A

No damage (H2O) again

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6
Q

If free radicals combine with other radicals?

A

Cause changes

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7
Q

If free radicals combine with molecules?

A

Can create toxins, ie H2O2 (hydrogen peroxide). Peroxide is very unstable and capable of producing widespread cellular changes

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8
Q

What can cause damage caused by x-rays to living tissue?

A
  • a direct hit and absorption of the x-ray photon within the cell (direct)
  • absorption of an x-ray photon by water within a cell resulting in the formation of a FREE RADICAL (indirect)
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9
Q

What are the 2 theories for how radiation damages biologic tissues?

A
  • direct theory

- indirect theory

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10
Q

What is the direct theory?

A

Theory about how radiation causes damage to biologic tissues. Cell damage results when ionizing radiation directly hits critical areas within the cell. Ex. x-ray hits DNA of the cell.

  • not frequent
  • most x-ray photons pass through the cell with little or no damage
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11
Q

What is the indirect theory?

A

Theory about how radiation causes damage to biological tissues. X-ray photons are absorbed within the cell and cause the formation of toxins, which in turn damage the cell. Ex. when x-ray photons are absorbed by water within a cell, free radical formation results

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12
Q

What is the dose-response curve?

A

Since all ionizing radiation is harmful, the dose-response curve is used to correlate the damage to tissue with the dose of radiation received.

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13
Q

What is the relationship shown on the dose-response curve?

A

Linear nonthreshold (what we use in dentistry)

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14
Q

Explain the linear nonthreshold relationship

A

Linear indicates that the response of the tissues is directly proportional to the dose. Nonthreshold dose-response curve suggests that no matter how small the amount of radiation received, some biological damage occurs. Overall, no matter the dose = still damage. Threshold is defined as the point at which a stimulus just produces a response, thus, the point at which a certain dose produces damage

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15
Q

Compare linear nonthreshold to a linear dose-response

A

Linear nonthreshold = see the response in time

Linear = see the response immediately

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16
Q

What are stochastic effects? What are some examples of stochastic effects?

A

Stochastic effects are delayed, they occur with chronic dose of radiation over long periods of time (ie occupational exposure) and as a direct function of the dose (dose causes it). No dose threshold = severity of effects do not depend on the magnitude of the absorbed dose.
When the dose of radiation is increased, the ‘probability’ of the the stochastic effect increases, but not the severity. Examples: cancer and genetic mutations

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17
Q

What are nonstochastic effects?

A

‘prompt effects’, large dose of radiation in a short period of time. The severity of the change is dependent on the dose. Effects increase in severity with increasing absorbed dose and for which a threshold value exists.. Examples: erythema, loss of hair, cataracts, decreased fertility

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18
Q

What is the latent period of radiation injuries?

A

The time that elapses between exposure to ionizing radiation and the appearance of observable clinical signs. Depends on the total dose of radiation received and the amount of time it took to receive the dose.

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19
Q

What is the period of injury?

A

After the latent period, where a variety of cellular injuries may result, like cell death, changes in cell function, abnormal or cessation of mitotic activity

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20
Q

What is the recovery period?

A

Not all radiation injuries are permanent, with each radiation exposure, depending on a number of factors, cells can repair the damage caused by radiation

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21
Q

What are cumulative effects

A

Effects of radiation exposure are additive and unrepaired damage accumulates in tissues the can lead to health problem, cancer, birth defects

22
Q

What are the determining factors for radiation injury?

A
  • total dose (more damage when tissues absorb large quantities of radiation)
  • dose rate (radiotherapy, cells have no time to repair - have to space out the dose)
  • amount of tissue irradiated (total body irradiation produces more adverse systemic effects than localized irradiation)
  • cell sensitivity (rapidly dividing cells and young cells)
  • age (more damage in children)
23
Q

What are the 4 radiation effects?

A
  • Short- and long-term effects
  • somatic and genetic effects
  • radiation effects on cells
  • radiation effects on tissues and organs
24
Q

What are short-term effects of radiation? What is ARS? What are some examples of short-term effects of radiation?

A
  • Short-term effects are seen within minutes, days or weeks
  • associated with large doses of radiation in a short amount of time (ex. exposure to nuclear accident)
  • acute radiation syndrome (ARS) is a short-term effect that includes nausea, vomiting, diarrhea, hair loss, hemorrhage
25
Q

What are long-term effects of radiation?

A
  • Small doses absorbed repeatedly over a long period of time

- effects seen after years, decades, or generations (cancer, birth abnormalities, genetic defects)

26
Q

What are somatic effects?

A

Somatic effects are effects on all cells in the body except the reproductive cells. Somatic effects are only ever seen in the person exposed to the radiation. not future generations

27
Q

What are genetic effects?

A

Effects on reproductive cells. Genetic effects are not seen in the person irradiated but passed on to future generations

28
Q

Radiation on cells: radiosensitive or radioresistent

A

Radiosensitive cells are cells that are sensitive to radiation
Radioresistent cells are cells that are resistant to radiation
Response is determined by mitotic activity, cell differentiation, cell metabolism

29
Q

Examples of radiosensitive organs

A

Lymphoid tissue, bone marrow, reproductive cells, intestines

30
Q

Examples of radioresistant tissues

A

Salivary glands, kidney, liver and muscle tissue

31
Q

What is a critical organ

A

An organ that, if damaged, diminishes the quality of a person’s life

32
Q

Examples of critical organs

A
  • skin
  • thyroid gland
  • lens of the eye
  • bone marrow
33
Q

What is the traditional system for measuring radiation?

A

Older units of radiation measurements. Includes
- Roentgen (R)
- radiation absorbed dose (rad)
- Roentgen equivalent (in) man (rem)
In dental radiography, Roentgen, rad and rem are all equal

34
Q

What is the SI international system of radiation measurement?

A

Newer units of radiation measurements. Includes

  • Coulombs/kilogram (C/kg)
  • Gray (Gy)
  • Sievert (Sv)
35
Q

Roentgen

A

Measures radiation by determining the amount of ionization that occurs in air. Does not describe the amount of radiation absorbed. Nothing equivalent in the SI system (exposure is states in coulombs per kilogram)

36
Q

What is dose?

A

Dose is the amount of energy absorbed by the tissue (radiation unit is rad, or radiation absorbed dose). SI equivalent is the gray

37
Q

What is the dose equivalent measurement?

A

Used to compare biologic effects of different kinds of radiation (traditional unit is the rem, or Roentgen equivalent man). SI equivalent is the sievert (1 Sv = 100 rem)

38
Q

When expressing small doses, we could use…

A

M to depict milli

Ex. Mrad or mrem

39
Q

Sources of radiation exposure

A

(natural background radiation)

  • cosmic radiation (originates from stars and sun, higher altitude = greater exposure to cosmic radiation)
  • terrestrial radiation (emitted from radioactive materials in the earth and air, from potassium-40, uranium)
  • artificial or man made radiation resulting from modern technology (includes consumer products, fallout from atomic weapons, weapons production, and the nuclear fuel cycle)
40
Q

What is the average dose of background radiation individuals may receive in the US?

A

150-300 mrads per year

41
Q

What is the potential risk of dental radiography producing a fatal cancer in an individual?

A

3 in 1 million

42
Q

What is the risk of a person spontaneous developing cancer?

A

3300 in 1 million

43
Q

How many mrads is the patient exposed to in 20 films (full mouth series)?

A

41 mrads

44
Q

How many mrads is the patient exposed to in 4 bitewings?

A

15 mrads

45
Q

How many mrads in a single x-ray?

A

2-6 mrads

46
Q

How many mrads does it take to produce cancer in the thyroid gland?

A

6000 mrads

47
Q

How many films does it take to produce cancer in bone marrow?

A

2000-5000 films per year

48
Q

How many dental films does it take to cause skin erythema?

A

500 dental films in 14 days

49
Q

How many mrads does it take to cause cataracts?

A

200,000 mrads (with about 3 mrads per x ray)

50
Q

What are 4 things that affect exposure?

A
  • Film speed (F vs D reduced by 60%)
  • Collimation (rectangular vs round by 60%)
  • Technique (longer distance to film from source reduces skin dose)
  • Exposure factors (higher KvP reduces skin dose)
51
Q

When should dental radiographs be prescribed?

A

Only when the benefits outweigh the risk or biological damage

Radiography (25 decks)

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