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Positioning Lecture Material > Radiobiology final > Flashcards

Radiobiology final Flashcards

1
Q

What factors contributed to high levels of skin dose in the early days?

A

long exposure times

low energy radiation

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2
Q

Which types of radiation is capable of ionization?

A

alpha and beta

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3
Q

Define background radiation:

A

the natural radiation that is always present in the environment. It includes cosmic, terrestrial and radiation

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4
Q

Define ionization:

A

removal or addition of an orbital electron from or to an atom

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5
Q

List the steps of the compton effect:

A
  1. An incident xray photon collides with an outer shell electron and is scattered with resulting energy loss
  2. The incident causes fog to the radiograph and exposure to the tech
  3. The electron is knocked out of orbit, frequency and wave length decreases, and the atom is ionized
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6
Q

List the steps of the photoelectric effect:

A
  1. The incident X-ray photon collides with the inner shell electron and is totally absorbed
  2. Is responsible for the white areas of the radiograph representing bone
  3. the atom is ionized
  4. secondary radtiation is emitted during the process, electrons from outer shells jump down to fill holes
  5. releases excess energy=characteristic radiation
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7
Q

Name the four statements of the Law of Bergonie and Tribondeau:

A
  1. stem cells undifferentiated are more radiosensitive
  2. young tissues and organs are more radiosensitive
  3. tissues with high metabolic activity are more radiosensitive
  4. tissues with high proliferation rate are more sensitive ex. bone marrow, blood cells, small bowel, spermatagonia
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8
Q

What is LET?

A

linear energy transfer-a measure of the rate at which energy is transferred to a tissue as ionizing radiation passes through it

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9
Q

What is RBE?

A

relative biologic effectiveness- an expression of the ability of various types of radiation to cause biologic damage relative to a standard radiation dose, which is always X-rays

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10
Q

How are LET and RBE related?

A

As the LET of radiation increases, the RBE also increases. They are directly proportional.

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11
Q

Which type of radiation has a high LET?

A

alpha

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12
Q

What does roentgen measure?

A

a unit that measures the amount of radiation as it passes thru air.

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13
Q

What does REM measure?

A

radiation equivalent man-effective dose- occupational or population dose

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14
Q

What does RAD measure?

A

radiation absorbed dose- measures absorbed energy into tissues

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15
Q

What does a curie measure?

A

radioactivity

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16
Q

How is the effective dose (Rems) calculated?

A

radiation weighting factor(Wr) x tissue weighting factor (Wt) x absorbed dose

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17
Q

What is radiation weighting factor?

A

(Wr)- an estimate of the ability of each type of radiation to cause biologic damage relative to the ionization ability of each. the Wr for X-rays is always 1 bc they are considered standard radiation in which all other types are compared to.

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18
Q

Define atomic number vs. atomic mass number:

A

atomic number- number of protons

atomic mass number-the number of protons and number or neutrons added together=weight of the atom

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19
Q

What is the net charge of the nucleus? Of the atom?

A

nucleus: +
atom: zero

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20
Q

Define binding energy and potential energy:

A

binding- strength of attachment of an electron to the nucleus
potential- electrons which are located in shells farther from the nucleus will posses more potential energy

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21
Q

Define attenuation:

A

the reduction in the total number of X-rays following penetration thru the matter

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22
Q

Define fractionation and protraction:

A

fractionation-a dose of radiation which is delivered to the body in fractions separated by time intervals
protraction-a continuous dose of radiation which is delivered to the body over a long period of time

23
Q

Differentiate between the dose response relationships of linear versus non linear:

A

linear= a straight line. As dose increases, the biologic response increase in direct proportion.

non linear= a curved line. As dose increases the biologic response can increase rapidly or slowly depending on the shape of the curve.

24
Q

Differentiate between the dose response relationships of threshold versus non threshold:

A

threshold=intersects above zero dose. In order for a biologic response to occur, a minimum dose of radiation is necessary. ex. skin burn takes 300 Rads

nonthreshold= intersects at zero. A biologic response always exists even at low doses but cannot be measured or seen. ex. genetic damage

25
Q

Which molecule in the body is most likely to interact with radiation?

A

water

26
Q

What type of interaction with radiation in the body will produce free radicals?

A

radiolysis of water

27
Q

Define the target theory: Which type of radiation is most likely to cause a direct hit? An indirect hit?

A
  • in order for a cell to die from radiation, its target or key molecule must be hit and inactivated.
  • high LET will most likely cause a direct hit
  • low LET most likely to cause an indirect hit
28
Q

Describe a chromosome aberration:

A

any change in the normal structure or number of chromosomes. often results in physical or mental abnormalities

29
Q

Which two cells in the body are most radiosensitive?

A

lymphocytes and spermatagonia

30
Q

How does the hemopoietic system respond the irradiation?

A
  • causes a reduction in RBC’s, WBC’S and platelets in blood.
  • body loses ability to fight infection
  • increase susceptibility for hemorrhage
  • results from whole body doses of 200-1000 Rads
31
Q

What are the three forms of acute radiation syndrome?

A
  • hematopoietic-200-1000 RAD
  • gastrointestinal-1000-5000 RAD
  • CNS-above 5000 RAD
32
Q

What are the symptoms of acute radiation syndrome?

A

Hematopoietic= vomiting, diarhea, malaise, lethargy, fever. Recovery is possible w/ bone marrow transplant. Death occurs from infection within 10-60 days

Gastrointestinal- severe nausea/vomiting/diarhea, bloody stools, hemorrhage, infection, fever, electrolyte imbalance. death caused by electrolyte imbalance, infection and dehydration and will occur within 4-10 days

CNS- disorientation, loss of muscle coordination, dyspnea, convulsions, seizures, loss of balance, coma. Death occurs from inter cranial pressure and increased fluid in the brain within 0-3 days.

33
Q

Name and describe the four stages of acute radiation syndrome:

A
  1. Promodol- occurs within minutes to hours and will last from hours to days w/ nausea/vomiting/diarrhea and fatigue. As dose levels increase the duration will decrease.
  2. Latent- period where there are no outward symptoms. Duration is from hours to weeks. As dose level increases latent period decreases.
  3. Manifest illness-period in which the affected systems clinical symptoms begin, may vary in severity.
  4. Death or recovery
34
Q

Define LD 50/30:

A

the whole body dose which will cause death in a period of 30 days to 50% of the population

35
Q

Define the following:

  • erythema
  • epilation
  • desquamation
A
  • redding of the skin following high dose of radiation
  • temporary loss of body hair following rad exposure
  • dry shedding of the skin following mild erythema
36
Q

Define late effects:

A

long term somatic effects that appear months or years later following chronic low level rad doses and acute whole body rad doses
-local tissues effects, life span shortening, carcinogenesis, and embryological effects

37
Q

Describe how exposure to radiation can cause cataracts:

A
  • threshold DDR
  • acute dose=200 rads, fractionated= 1000 rads
  • high LET has greater effect
38
Q

Name the study groups who suffered radiation induced malignancies:

A

a-bomb survivors
radiotherapy patients
early nuclear physicists who worked with cyclotrons

39
Q

Define the inverse square law and know how to calculate it:

A

as the distance from the rad source increases the exposure decreases in inverse proportion to the square of the distance.
double your distance=decreases to 1/4 of its original value
triple your distance=decreases to 1/9
quadruple your distance=decreases to 1/16

40
Q

Define:
Reproducibility
Linearity

A

R-for any given radiographic technique setting, the output of rad intensity should be constant from one exposure to the next
L-when different mA stations are used in different combos to obtain the same mAs, the output should be constant.

41
Q

What should the source to table top distance be for stationary units? mobile units? What intensity must the X-ray intensity never exceed?

A

15” for stationary
12” for mobile
10R/min

42
Q

Define the half value layer:

A
  • the thickness of absorbing material necessary to reduce the X-ray intensity to one half of its original value. It measures the X-ray beam quality or penatrability.
  • as kvp ^ HVL ^
43
Q

Distinguish between the variable aperture collimation and positive beam limitation:

A

VAC=modern day collimators, beam is adjustable

PBL=automatic collimators that limit the beam to the exact film size

44
Q

What are the components located within the variable aperture collimator box and what are their purposes?

A
  • entrance shutter=absorbs off focus radiation
  • long shutters=controls length wise of collimated beam
  • cross shutters= controls width wise of collimated beam
  • light source=projects light beam onto reflecting mirror
  • plastic exit portal=provides cross hairs for centering
  • added filtration= brings total filtration to 2.5 mm
45
Q

Compare primary and secondary protective barriers:

A

Primary=must be provided whenever the primary beam intersects at a perp angle, must be equivalent to 1/16” lead

Secondary= provided whenever scatter or leakage radiation intersects the wall in question ex. shielded control booth. must be 1/32” lead equivalent

46
Q

What are the basic types of personal monitoring devices?

A

film badge-most widely used, capable of recording a slowly accumulated dose

thermoluminescent dosimeter-records exposures as low as 5 mrem

ionization chamber(pocket dosimeter)-suited for high exposure areas where an immediate reading is recommended

optically stimulated luminescence dosimeter-can record exposures as low as 1 mrem

47
Q

What is the estimated skin dose during fluoro?

A

4-8 R/min

48
Q

Define GSD:

A
  • average rad exposure to the gonads of the US population- direct exposure/scatter.
  • about 20mrads in US
  • assumes that the dose would have the same genetic effect on unexposed individuals as those who were actually exposed
49
Q

Name and describe the various types of beam restricting devices:

A

aperture diaphragm-flat piece of lead lined metal with a hole in the middle.

cone-circular metal tubes which restrict the useful beam to desired size

collimators-box like structure with adjustable diaphragmn

50
Q

What is the average fluoro mA.02?

A

1-5 mA

51
Q

What is the most radiosensitive phase of the cell cycle?

A

metaphase

52
Q

What is the sensing phosphor in the TLD?

A

lithium fluoride , crystal emits visible light when heated, light is in proportion to rad detected

53
Q

What is the required amount of total filtration for X-ray tubes operating above 70 KVP?

A

2.6 mm Al

Positioning Lecture Material (10 decks)

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