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MRS > Section 2 > Flashcards

Section 2 Flashcards

1
Q

What does LET stand for

A

Linear Energy Transfer

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2
Q

What does LET do

A

energy deposited per length

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3
Q

Greater LET means

A

greater damage

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4
Q

What particles have increased LET?

A

alpha and protons

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5
Q

Are the 5 MV x-rays more or less damaging than the 250 kVp x-rays?
More damaging

A

more damaging

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6
Q

What does RBE stand for

A

relative biological effectiveness

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7
Q

Why is RBE important?

A

damaging ability of radiation relative to 250kVp

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8
Q

Recall the formula for RBE

A

RBE = (dose of 250kVp to produce effect)// (dose of test radiation to produce same effect)

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9
Q

Greater than 1 RBE means

A

more damaging

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10
Q

Lesser than 1, RBE means

A

less damaging

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11
Q

Spreading the dose over time

A

leads to less damage

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12
Q

acute exposure refers to

A

rapid exposure/dose

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13
Q

chronic exposure refers to

A

long lasting duration

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14
Q

Fractionation is where

A

same dose rate but split into fractions (used in RT and rate = Gy/hr)

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15
Q

Protraction is where

A

same dose (Gy), continuously delievered at a lower rate so the overall amount of gray stays the same (longer period of time)

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16
Q

Older cells are more

A

radioresistant

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17
Q

Younger cells are more

A

radiosensitive

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18
Q

increased radiosensitivity

A

causes increased metabolic rate and increased proliferation rate

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19
Q

aerobic tissue is

A

oxygenated

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20
Q

Aerobic tissue is more

A

sensitive than anoxic and hypoxic

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21
Q

anoxic

A

no oxygen

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22
Q

hypoxic

A

low oxygen

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23
Q

OER =

A

dose under anoxic// dose under aerobic

24
Q

OER is always

A

greater than 1

25
Q

OER is always higher for

A

low LET radiation

26
Q

For high LET, OER

A

will be reduced to 1 (approaches it)

27
Q

As we age, our ability to repair our

A

cells become less effective

28
Q

When do we have high sensitivity to radiation?

A

Before Birth & elderly

29
Q

What is the excess risk for a foetus?

A

6% per Gy - for 1Gy, there will be risk of 6%

30
Q

Pre implantation is the

A

fertilisation (9 day period)

31
Q

Major organogenesis (week 2-8) is

A

point of development where cells are replicating and specialising
main risk is embryonic malformations

32
Q

fetal growth (weeks 8-40) is

A

prenatal death & congenital abnormalities are negligable
- main risk is the nervous system and sense organs

33
Q

dose response relationships describe

A

effects (risk) vs amount of radiation (dose)

34
Q

What are the 2 kinds of responses?

A

deterministic and stochastic

35
Q

Deterministic (cause & effect) is

A

health effects directly related to dose
- no uncertainity/ambiguity

36
Q

Stochastic (random) is

A

occurance by chance & probability increases with dose

37
Q

Linear Non-Threshold

A

is where risk is proportionate to dose

38
Q

LNT model says that any dose

A

will produce biological effects - there is no safe dose

39
Q

The LNT model is used to evaluate risk because

A

it gives the best guess of the worst case scenario NOT because it matches all evidence

40
Q

Radiation Hormesis is where

A

low radiation doses are beneficial - we do not adopt this model

41
Q

absolute risk is the

A

actual # of cases in a group (# or %)

42
Q

excess risk is the

A

observed cases/rate - expected case/rate

43
Q

relative risk is the

A

observed//expected

44
Q

BERT is a useful tool to

A

explain how much radiation a patient will receive

45
Q

patients have no

A

dose limits

46
Q

Why do patients not have dose limits?

A

benefit > risk

47
Q

public dose limit is

A

1mSv per year

48
Q

Occupational dose limit is

A

20mSv/year, averaged over 5 consect. yrs

49
Q

ICRP fundamentals for radiation protection is

A

justification (benefit > risk); limitation (follow rules);
optimisation (ALARA)

50
Q

Limitation & optimisation measures include

A

time (minimise time near source); distance (maximise distance from source); shielding (lead apron and walls)

51
Q

For scattered and leadkage of radiation, we use

A

secondary barriers

52
Q

The relative risk model

A

is where risk increases with age

53
Q

Linear Non threshold is

A

there is no observable biological response at low doses until a point at which a biological response occurs

54
Q

The radiation hormesis model states that

A

low dose exposure to a physical or biological agent helps the body & as dose increases, the good effects decrease (graph)

55
Q

Radiation that scatters off a patient in a DR scan is considered to be a

A

secondary source

MRS (12 decks)

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