Dosimetry Flashcards

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1
Q

What are the radiation core safety principles?
(3)

A

Justification

Optimisation

Limitation

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2
Q

How do we know that radiation is harmful?

A

Atomic bomb survivors

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3
Q

How do atomic bomb survivors tell us that radiation is harmful?

A

Survivors were tested for how close they were from the epicentre, which indicated the dose that they received. The further they were, the less dose they got. They compared the number of cancers these people got to a normal population.

The further the distances from the epicentre, the lower occurrence of cancer. This allowed the creation of the linear non-threshold model for stochastic effects

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4
Q

What does the linear non-threshold model for stochastic effects say?

A

The higher the dose of radiation someone receives, the higher their risk of cancer

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5
Q

Why may the linear non-threshold model for stochastic effects be inaccurate?

A

Because the information to create it was from atomic bomb survivors, yet all of them had high doses- just in different quantities

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6
Q

What are the 2 types of quantities of radiation?

A

Direct quantities (radiation that’s directly measured)

Derived quantities (radiation that’s not directly measured)

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7
Q

What are the direct quantities of radiation?
(3)

A

Exposure

KERMA

Absorbed dose

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8
Q

What are the derived quantities of radiation?
(5)

A

Equivalent dose

Effective dose

DAP

DLP

Personal dose equivalent

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9
Q

What is exposure?

A

The amount of ionisation caused by an x-ray or a gamma ray in air

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10
Q

What does the exposure measure?

A

The total charge produced in air by ionising radiation

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11
Q

What does the exposure not include?

A

The extra ionisation caused by the slowing of electrons (brehmstrahlung)

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12
Q

What is the unit of exposure?

A

Coulombs per kilogram (C/kg)

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13
Q

What direct quantity is usually used instead of exposure?

A

KERMA

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14
Q

What is KERMA?

A

A measure of kinetic energy released per unit mass. It includes the effects of brehmstrahlung

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15
Q

What is the unit for KERMA?

A

Gray (Gy)

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16
Q

What is the absorbed dose?

A

The amount of energy deposited in a material

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17
Q

What is the absorbed dose equal to?

A

KERMA in air

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18
Q

What is the unit for the absorbed dose?

A

Gray (Gy)

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19
Q

What is linear energy transfer (LET)?

A

It defines how damaging a radiation is based on charge, mass and energy

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20
Q

What does it mean if there’s a higher LET?

A

The DNA breaks are more irreparable

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21
Q

Do alpha particles have a high or low LET?
Why?

A

High LET

So that they can slow down quickly in tissue and cause more damage in the DNA

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22
Q

Do gamma rays, x-rays and electrons have a high or low LET?

A

Low LET

23
Q

What is the relative biological effectiveness (RBE) determined by?
(3)

A

The LET of the radiation

The dose rate

The particle type

24
Q

What is the equivalent dose?

A

It considers the harmfulness of the radiation

25
Q

What is the unit for the equivalent dose?

A

Sievert (Sv)

26
Q

What is the weighting factor for beta, gamma and electrons?

A

1

27
Q

What is the weighting factor for protons?

A

5

28
Q

What is the weighting factor for neutrons?

A

5-20

29
Q

What is the weighting factor for alpha?
Why?

A

20

Because it causes more damage

30
Q

When can DNA only be damaged?

A

When it’s condensed

31
Q

What is the main unit when looking at the risk of radiation?

A

Effective dose

32
Q

Why are some organs in the body more sensitive to radiation than others?

A

Because the faster the organs divide, the more of them are in the stationary (S) phase in the cell cycle, so the DNA is condensed and can be more easily damaged

33
Q

What is the unit of the effective dose?

A

Sievert (Sv)

34
Q

Which type of dose do we use to find out the risk?

A

Effective dose

35
Q

What is the effective dose of ultrasound and MRI?
Why?

A

0

Because they don’t involve ionising radiation

36
Q

Why do children and foetuses have a greater risk associated with radiation exposures?
(2)

A

Because they live longer, so there’s more time for cancers to develop

Because they’re growing

37
Q

What does DAP stand for?

A

Dose
Area
Product

38
Q

What is the exposure area product?

A

The exposure measured using a transparent flat-bed ion chamber attached to an x-ray collimator

39
Q

What is the exposure area product commonly known as?

A

Te absorbed dose that’s being delivered to the patient in the air

40
Q

What does ESD stand for?

A

Entrance
Surface
Dose

41
Q

What is the entrance surface dose?

A

The absorbed dose at the entrance surface of the patient (the dose to the skin). It includes back-scattered radiation

42
Q

What does CTDI stand for?

A

CT
Dose
Index

43
Q

What is the CTDI?

A

The dose that would’ve been measured if the output had been equal to the chosen slide width

44
Q

What is CTDIvol?

A

How to measure the absorbed dose with a rotational x-ray beam

45
Q

What does CTDIvol stand for?

A

CT
Dose
Index for a
Volume

46
Q

What factors impact what CTDI volume is delivered?
(2)

A

Collimation

Pitch

47
Q

What are occupational exposures?

A

Exposures to a risk in the workplace (doses expoed to staff)

48
Q

What can be used to measure the dose of staff?

A

Dosimeters

49
Q

What are AECs?

A

The use of ionisation chambers to optimise exposure

50
Q

What does AEC do?

A

It monitors the dose received at the detector and terminates x-rays when the dose is what has been specified

51
Q

What are the 3 AEC chambers?

A

A
B
C

52
Q

What AEC chambers do we use for a thicker material?
(2)

A

A
B

53
Q

What AEC chambers do we use for a thinner material?

A

C