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Dose Tolerances > Radioactive Isotopes > Flashcards

Radioactive Isotopes Flashcards

1
Q

Half-life of Ra-225

A

1600 years

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2
Q

Half-life of Rn-222

A

3.83 days

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3
Q

Half-life of Co-60

A

5.26 yrs

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4
Q

Half-life of Cs-137

A

30 yrs

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5
Q

Half-life of Ir-192

A

73.8 days

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6
Q

Half-life of Au-198 (gold)

A

2.7 days

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7
Q

Half-life of I-125

A

59.4 days

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8
Q

Half-life of Pd-103

A

17 days

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9
Q

Photon E (MeV) of Radium

A

0.83 avg

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10
Q

Photon E (MeV) of Rn-222

A

0.83 avg

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11
Q

Photon E (MeV) of Co-60

A

1.17; 1.33 (1.25 avg)

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12
Q

Photon E (MeV) of Cs-137

A

0.662

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13
Q

Photon E (MeV) of Ir-192

A

0.38 avg

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14
Q

Photon E (MeV) of Au-198

A

0.412

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15
Q

Photon E (MeV) of I-125

A

0.028 avg

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16
Q

Photon E (MeV) of Pd-103

A

0.021 avg

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17
Q

Exposure Rate Constant (Γ) of Radium

A

8.25 R-cm^2/mg-hr

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18
Q

Exposure Rate Constant (Γ) of Rn-222

A

10.15 R-cm^2/mCi-hr

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19
Q

Exposure Rate Constant (Γ) of Co-60

A

13.07 R-cm^2/mCi-hr

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20
Q

Exposure Rate Constant (Γ) of Cs-137

A

3.26 R-cm^2/mCi-hr

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21
Q

Exposure Rate Constant (Γ) of Ir-192

A

4.69 R-cm^2/mCi-hr

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22
Q

Exposure Rate Constant (Γ) of Au-198

A

2.38 R-cm^2/mCi-hr

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23
Q

Exposure Rate Constant (Γ) of I-125

A

1.46 R-cm^2/mCi-hr

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24
Q

Exposure Rate Constant (Γ) of Pd-103

A

1.48 R-cm^2/mCi-hr

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25
Q

Natural log of 2

A

ln2 = .693

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26
Q

Decay Constant formula

A

λ = .693/T1/2

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27
Q

Half Life formula

A

T1/2 = .693/ λ

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28
Q

Mean/Avg Life formula

A

Ta = 1.44 x T1/2

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29
Q

Activity formula

A

A = Ao x e^(- λt)

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30
Q

Total Dose formula

A

TD = Ta x output;
or
TD = 1.44 x T1/2 x Do
(Do = dose ouput)

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31
Q

Formula used to determine exposure by radioactive isotope:

A

X = Γ x (A/(r^2)) x t

r=distance

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32
Q

Formula used to convert source to Ra Equivalent

A

A x( Γ / (8.25Rcm2/mg-hr))

Γ = exposure rate constant of source

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33
Q

Formula used to determine dose distribution of radioactive isotope

A

Γ x mgRa Eq Source x (d1/d2)^2

ex. Dose rate at 9cm from 10mgRa eq source = 8.25 x 10 x (1/9)^2

**used after source has been converted to mgRa Equivalent

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34
Q

Decay per year (%) for Pd-103

A

100%

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35
Q

Decay per year (%) for I-125

A

98.5%

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36
Q

Decay per year (%) for Ir-192

A

96.7%

37
Q

Decay per year (%) for Co-60

A

12.3%

38
Q

Decay per year (%) for Cs-137

A

2.3%

39
Q

How many half-lifes until a radionuclide is gone?

A

10 half-lifes

40
Q

Rule of Thumb: Cs-137 decays _____?

A

1% per 6 months

41
Q

Rule of Thumb: Co-60 decays _____?

A

1% per month

42
Q

Rule of Thumb: Ir-192 dcays ____?

A

1% per day

43
Q

Describe Secular Equilibrium

A
  1. half-life of parent&raquo_space;> half-life of daughter;
  2. decay constant of daugher&raquo_space;> decay constant of parent;
    ex. Ra-226 (parent) and Rn-222 (daughter)
44
Q

Describe Transient Equilibrium.

A
  1. half-life of parent > half-life of daughter;
  2. decay constant of daughter > decay constant of parent
    ex. Mo-99 (parent) and Tc-99m (daughter)
45
Q

HVL (mm Pb) for Ra-226

A

8mm

46
Q

HVL (mm Pb) for Cs-137

A

5.5 mm

47
Q

HVL (mm Pb) for Co-60

A

11mm

48
Q

HVL (mm Pb) for Au-198

A

2.5mm

49
Q

HVL (mm Pb) for Ir-192

A

2.5mm

50
Q

HVL (mm Pb) for I-125

A

0.025mm

51
Q

HVL (mm Pb) for I-103

A

0.008mm

52
Q

What is the Air KERMA equation:

A

U = uGy - m^2/hr

**can be measure in Gy or distance

53
Q

What isotopes are used for prostate brachy (LDR)

A

I-125 and Pd-103

54
Q

Disadvantage of Rn-222 and what replaced it?

A

leakage; Cs-137

55
Q

Advantages of Cs-137

A
  1. less hazardous
  2. less shielding
  3. Same penetrating power as Radium up to 10cm
56
Q

Define the location of Point A for T and O

A

2cm superior of Os, 2cm lateral of cervical canal

57
Q

What is typical dose for Point A of T and O

A

0.35 (tandem) + 0.19 (Ovoid) = 0.54 Gy/hr

58
Q

Define the location of Point B of T and O

A

2cm superior of Os, and 5cm lateral from midline

59
Q

What is the typical dose for Point B of T and O

A

Pt B dose = Pt A dose / 3

60
Q

What is the physical length of a Cs-137 source

A

2cm

61
Q

What is the active length of a Cs-137 source

A

1.4-1.5cm

62
Q

Define Source Anisotropy

A

Self-Attenuation

63
Q

At what distance must ISL be accounted for, for a line source

A

at 2x the source length

64
Q

ISL must be used to account for source strength for what type a source

A

point source

65
Q

What is Sr-90 and what is it used to treat?

A

Strontium-90; Pterygium

66
Q

What is the E and half-life of Sr-90 compared to Y-90

A 
Sr-90 = 540 keV B-; T1/2 = 28.5 years
Y-90 = 2.2 MeV B-; T1/2 = 64.2 hours
67
Q

What radionuclide is used for Thyroid Ablation, and what is the typical dosage?

A

I-131; 100mCi - 200mCi

68
Q

What is the physical and biological half-life of I-131?

A 
Physical = 8 days
Biological = 12 days
69
Q

Formula for Effective half-life:

A

Effective half-life = (Tb x Tp) / (Tb + Tp)

*Tb = biological half-life; Tp = physical half-life

70
Q

Typical Rx for prostate seed implant (LDR):

A

Primary: I-125 = 144Gy; Pd-103 = 115Gy
Boost: I-125 = 120Gy; Pd-103 = 90Gy

71
Q

Dose Rate of I-125

A

5-10 cGy/hr

72
Q

Dose Rate of Pd-103

A

20-30 cGy/hr

73
Q

Dose Rate of Au-198

A

64 cGy/hr

74
Q

Where in the prostate are seeds implanted, why?

A

peripheral; to stay off urethra

75
Q

What is max dose to Urethra for brachy prostate (LDR)

A

<150% of Rx

76
Q

How many seeds are ordered for brachy prostate (LDR)

A

10% more than needed

77
Q

ICRU-38 LDR dose rate:

A

0.4 Gy/hr to 2.0 Gy/hr, OR

40 rad/hr to 200 rad/hr

78
Q

ICRU-38 MDR dose rate:

A

2.0 Gy/hr to 12 Gy/hr, OR

200 rad/hr to 1200 rad/hr

79
Q

ICRU-38 HDR dose rate:

A

> 12 Gy/hr, OR

>1200 rad/hr

80
Q

What source is used for HDR prostate, and what is the initial strength when ordered?

A

Ir-192; 10 Ci

81
Q

Daily QA for Brachy afterloader include?

A

Interlocks, Source Positioning (+-1mm), Area Monitor (GM)

82
Q

Quarterly QA for Brachy afterloader?

A

Calibration (re-entrant chamber); Source Positioning (film); Emergency Source Retraction; Adaptors

83
Q

Advantages of HDR:

A
  1. Rad Protection
  2. Decrease Human Error
  3. Optimized dose
  4. More accurate
  5. decreased pt discomfort
  6. Outpatient
  7. Avoid General Anesthesia
  8. Scheduling
84
Q

Disadvantages of HDR:

A
  1. Can’t take back dose
  2. Rad-bio (depending on fractionation)
  3. Source Cost
85
Q

For HDR planes and dwell positions are separated by ___

A

1cm

86
Q

What is the basal dose point?

A

the geometric center of triangles

87
Q

What is the typical dose for Mammosite?

A

10 fx at 340cGy - TD = 34 Gy (3400cGy), BID

88
Q

Where is Rx point located for Mammosite?

A

1cm from ballon

89
Q

Symmetry of balloon for Mammosite:

A

<2mm symmetric

Dose Tolerances (23 decks)

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