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Radiation Biology > Cellular Repair > Flashcards

Cellular Repair Flashcards

1
Q

Parameters of radiation exposure

A
  1. total dose absorbed
  2. rate at which dose delivered
  3. quality of the radiation
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2
Q

Acute radiation sickness syndrome

A

4-24 hrs after exposures

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3
Q

what determines whether subjects live or die after TBI

A

hematopoietic system

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4
Q

Lethal damage (LD)

A

irreversible and irreparable

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5
Q

Sublethal Damage (SLD)

A

repairable in hours unless additional SLD added

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6
Q

Potential Lethal Damage (PLD)

A

component of radiation damage that can be modified by post irradiation environmental conditions.

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7
Q

LD 50 for radiation

A

4.5 Gy

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8
Q

CNS syndrome time frame

A

hours

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9
Q

GI syndrome time frame

A

3-10 days

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10
Q

Hematopoietic syndrome time frame

A

30 days

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11
Q

PLD environmental conditions

A

incubate cells in salt solution. delay mitosis through suboptimal growth conditions –gives DNA chance for repair

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12
Q

PLDR

A

Potential Lethal Damage Repair - usually occurs in G0 - G1 cells

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13
Q

Culture conditions that facilitate PLDR

A
  1. post radiation maintenance
  2. culture conditions suboptimal for cell cycle progression
  3. isotonic media or chemicals that inhibit DNA synthesis
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14
Q

SLDR

A

Sublethal Damage Repair - repair of radiation lesions progresses as a time dependent function

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15
Q

Elkin and Sutton concept

A

shoulder of the dose-survival curve reflects the ability of the cell to accumulate sublethal radiation damage.

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16
Q

SLD recover time

17
Q

Fractionation

A
  • normal cells recover while tumor cells have less time to repair.
  • tumor cells in radioresistant phase in one treatment will be sensitive in next
  • re-oxygenation b/w fractions
18
Q

hyper-fractionation

A
  • small fractions (<2 Gy)
  • bronchus, cervix, uteri, head, neck
  • less sensitive than late-responding healthy tissues to fraction size
19
Q

hypo-fractionation

A
  • fewer fractions more than 2 Gy

- similar fractionation sensitivity to healthy tissue

20
Q

Therapeutic doses

A

curative cases:
epithelial 60-80 Gy
lymphoma 20-40 Gy

21
Q

Preventative doses

A

(aka adjuvant dose)

-45-60 Gy in 1.8 - 2 Gy fractions

22
Q

Typical Fractionation schedule

A

1.8-2 Gy per day 5 days per week

23
Q

Child fractionation dose

A

1.5-1.8 Gy per day

24
Q

concomitant boost regimen

A

two fractions in a single day (used near end of course of treatment)

25
Q

alpha/beta value

A

quantifies sensitivity to fraction size

26
Q

linear-quadratic clinical response function

A

alpha x D + B x D^2

27
Q

D in linear quadratic clinical response function

A

fraction size

28
Q

low alpha/beta

A

increased responses for fractions sizes greater than 2 Gy

29
Q

BED2

A

Biologically effective Dose - in 2 Gy fractions

30
Q

4 R’s of radiobiology

A

Repair
Reassortment
Repopulation
Reoxygenation

31
Q

SLDR mechanism

A

dsDNA break rejoining before second dose occurs

32
Q

Dose Rate Effect

A

lower the dose = reduced biologic effect

33
Q

Inverse dose rate effect

A

decrease dose rate = increased cell killing

continuous low dose means cells trapped in G2

34
Q

Very low dose rates

A
  • steady state cell population
  • cells accumulate in G2
  • species specific
35
Q

Reoxygenation

A

fractionation give cells time to re-oxygenate

36
Q

OER

A

Oxygen enhancement ratio - ratio of doses administered hypoxic to aerated conditions

37
Q

chronic hypoxia

A

due to limited diffusion range of oxygen in tissue

38
Q

acute hypoxia

A

temporary closing of tumor blood vessels

39
Q

Principal factor leading to development of necrotic area in tumors

A

oxygen depletion

Radiation Biology (10 decks)

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