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CORE Physics > Dose trivia > Flashcards

Dose trivia Flashcards

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1
Q

absorbed dose unit

A

Gy (J/kg)

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2
Q

What is the threshold for permanent sterility in males from an acute exposure, approximately?

A

6 Gy

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3
Q

Individuals who work in facilities in which radiation sources are used but whose responsibilities do not include exposure radiation are permitted to be exposed up to how many mrem per year?

A

100 mrem whole body

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4
Q

What does the radiation unit of absorbed dose measure?

A

Amount of energy absorbed per unit mass from ionizing radiation

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5
Q

The threshold dose for the main erythema reaction in human skin is ?

A

5 Gy The terms as defined by the International Commission on Radiological Protection (ICRP) include an early transient erythema seen a few hours after doses of 2 Gy. The main erythema reaction is at ~ 10 days and is secondary to inflammation and cell death of the basal epidermal layer and occurs at ~ 5 Gy. A late erythema can be seen 8-10 weeks after exposure and is bluish secondary to ischemic changes (~ 15 Gy).

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6
Q

The threshold dose for the early transient erythema in human skin is ?

A

2 Gy The terms as defined by the International Commission on Radiological Protection (ICRP) include an early transient erythema seen a few hours after doses of 2 Gy. The main erythema reaction is at ~ 10 days and is secondary to inflammation and cell death of the basal epidermal layer and occurs at ~ 5 Gy. A late erythema can be seen 8-10 weeks after exposure and is bluish secondary to ischemic changes (~ 15 Gy).

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7
Q

The unit of kinetic energy released in a mass (kerma) is a measure of?

A

Kinetic energy released in a mass (kerma) is a measure of the total initial kinetic energy of all charged particles liberated by uncharged particles per unit mass. It has units of J/kg, or Gy.

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8
Q

CTDI definition

A

CT dose index The CT dose index (CTDI) is a measure of the dose per slice as estimated with a 16 cm or 32 cm acrylic phantom as measured over a 100 mm length. CTDIvol takes into account the effect of mAs, kVp, and pitch as well as the difference in dose at the periphery and center of the phantom (CTDIvol = (1/3 x CTDI100 [center] + 2/3 x CTDI100 [periphery])/pitch).

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9
Q

Is CT scan length taken into account with CTDI or DLP?

A

DLP (dose length product) DLP = CTDvol x scan length

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10
Q

Radiation dose increases _____________with scan length

A

linearly

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11
Q

regulatory dose for fluoro (no high level control)

A

87 mGy/min (10 R/min)

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12
Q

regulatory dose for fluoro (high level control)

A

176 mGy/min (20 R/min)

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13
Q

What parameter must be set for High level control?

A

an audible alarm must be on when HLC is used

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14
Q

operator dose at 1 m from fluoro table

A

0.1% of what the patient gets

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15
Q

operator regulatory dose limit

A

50mSv/yr

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16
Q

fetus dose limit of operator

A

0.5mSv per mo

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17
Q

permanent epilation dose

A

7 Gy

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18
Q

at what dose does a physicist need to review the case?

A

> 5 Gy

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19
Q

Dry desquamation dose

A

13 Gy

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20
Q

Moist desquamation dose

A

18 Gy

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21
Q

Secondary ulceration

A

24 Gy

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22
Q

13 Gy

A

Dry desquamation dose

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23
Q

18 Gy

A

Moist desquamation dose

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24
Q

24 Gy

A

Secondary ulceration

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25
Q

CT Accreditation program developed by the ACR has established diagnostic CT reference values. What is the CTDvol for a routine adult abdomen?

A

25 mGy

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26
Q

According to Nuclear Regulatory Commission regulations, what is the annual dose limit for occupationally exposed individuals for the whole body, lens, and extremities?

A

5 rem to the whole body 15 rem to the lens 50 rem to the extremities

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27
Q

The maximum dose an individual member of the public may receive from the release of patients injected with radioactive materials (e.g., thyroid ablation patients)

A

5 mSv (500 mrem) is the maximum dose an individual member of the public may receive from the release of patients injected with radioactive materials.

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28
Q

The dose limit to a general member of the public from activities performed involving the use of radiation

A

1 mSv (100 mrem)

29
Q

difference between CTDIw and CTDIvol

A

Weigthed CTDI takes into account the difference between the dose at the periphery (about double the center) and dose at the center. It is calculated by 1/3 the central CTDI + 2/3 the periphery CTDIw is expressed in mGy (no volumetric or length data - JUST DOSE) Volume CTDI (CTDIvol) is obtained by divided CTDIw by the pitch (CTDIvol = CTDIw/pich)

30
Q

CTDIw and CTDIvol unit

A

mGy

31
Q

equation for CTDIw

A

1/3 central CTDI + 2/3 peripheral CTDI

32
Q

DLP equation

A

DLP = CTDI vol x length of scan

33
Q

CTDIvol equation

A

CTDIw/pitch

34
Q

units of DLP

A

mGycm

35
Q

units of effective dose for CT

A

Sv

36
Q

equation for effective dose in CT

A

effective dose = k x DLP

37
Q

size of CT phantoms1

A

32 cm adult; 16 cm peds

38
Q

CTDI numbers are based on:

A

CT phantoms. body phantom is 32 cm, peds phantom is 16 cm

39
Q

ACR reference values CTDIvol: head, adult abdomen, peds abdomen

A

75mGy for head; 25 mGy for adult abd; 20 mGy for peds abd (5 yo) Ference dose is set by the ACR at the 75th percentile, and doses above this level should be investigated. These values are different from average dose

40
Q

if patient larger than CT phantom, dose is __________estimated

A

if patient larger than CT phantom, dose is OVER estimated

41
Q

if patient smaller than CT phantom, dose is __________estimated

A

if patient smaller than CT phantom, dose is UNDER estimated

42
Q

dose is UNDER estimated when patient is _______ than the CT phantom

A

dose is UNDER estimated when patient is smaller than the CT phantom

43
Q

dose is OVER estimated when patient is _______ than the CT phantom

A

dose is OVER estimated when patient is larger than the CT phantom

44
Q

average dose in adult head CT

A

60 mGy

45
Q

average dose in adult abd CT

A

20 mGy

46
Q

average dose in peds abd CT

A

15 mGy

47
Q

effective dose in adult head CT

A

1-2 mSv

48
Q

effective dose in adult abd CT

A

8-11 mSv

49
Q

dose of 1 CT chest is equal to about _____ PA CXRs

A

1 CT = 100 CXRs

50
Q

CT of extremity effective dose

A

< 1mSv (super duper low) because extremities don’t contain any radiosensitive organs

51
Q

embryo dose in CT A&P

A

30mGy

52
Q

when is individual dose monitoring mandated?

A

when the occupational dose is >10% the annual dose limit of 500 mrem

53
Q

risk of radiation induced cancer per dose in adult vs child

A

adult: 5% per Sv. child: up to 15% per Sv

54
Q

maximum annual total effective dose equivalent for a worker under 18

A

NRC annual occupational dose limit for minors is 10% of adult dose limits. For total effective dose equivalent for adults is 50 mSv (0.05 Sv). The limit for a minor is 5 mSv (0.005 Sv) 5mSv is the same limit as for a fetus

55
Q

32 cm acrylic phantom is placed in the CT gantry. The following measurements were obtained with the pitch set at 1.25: CTDI periphery = 30 mGy and CTDI center = 15 mGy. What is the CTDIvol?

A

20 mGy CTDIw is calculated as (1/3) CTDIcenter + (2/3) CTDI periphery. The CTDIvol = CTDIw/Pitch (1/3)(15) + (2/3)(30) = 25 25/1.25 = 20

56
Q

background radiation

A

3 mSv (300mrem)

57
Q

dose limit to member of general public

A

1 mSv (100 mrem)

58
Q

Total effective dose limit for a radiation worker

A

50 mSv (500mrem)

59
Q

dose limit for a radiation worker’s lense

A

150 mSv

60
Q

dose limit for a radiation worker’s extremity

A

500mSv (50,000 mrem, 50 rem)

(1 Sv = 100 rem)

61
Q

1 Sv = ________rem

A

1 Sv = 100 rem

62
Q

1 mSv = ________mrem

A

1 mSv = 100 mrem

63
Q

100 mrem = _______mSv

A

100 mrem = 1 mSv

64
Q

100 rem = _______Sv

A

100 rem = 1 Sv

65
Q

estimated absorbed dose to fetus from a routine abdomen pelvis

A

25 mGy

66
Q
A

2.5 mGy.

Use inverse square law, the dose at point B will be 4 times less than the dose at point A since the distance was doubled. So, 10/4 = 2.5 mGy

67
Q

a medical event must be reported if:

A
68
Q

a pregnant patient inadvertently adminstered I-131 for Grave’s disease.

at what gestational age would the infant be at greatest risk for radioactive iodine-induced creatism

A

10-12 weeks

69
Q

29 yo patient who is 10 weeks pregnant undergoes CT scan with estimated fetal absorbed does of 25 mGy. Increased risk of:

A

2x increased risk of cancer at 25 mGy

  • For dose < 50 mGy –> no risk of birth defect, intellectual disability or fetal death
  • > 100 mGy higher increase in adverse effects
    • 1-2 weeks (preimplantation period) : there is an increased risk of death.
    • 3-8 wk (organogenesis): increased risk of severe birth defects
    • 9-15 wk: increased risk of mental retardation

CORE Physics (21 decks)

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