Flashcards in Brachytherapy Quiz Deck (56)
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1
Iridium-192 (Ir-192) half life
73.8 days
2
Ir-192 clinical use
"Grain of rice" high dose rate (HDR) in remote afterloader for GYN and prostate interstitial implants; high specific activity (A) (HDR increases specific A)
3
Activity (A) per volume/unit of mass a radioactive material that dictates the total A a small source can have (Ci/g)
Specific activity
4
High activity/dose in a small volume
High specific activity
5
Iodine-131 (I-131) clinical use
Thyroid ablation uptakes iodine
6
Radon-222 (Rn-222) half life
3.83 days
7
Daughter of radium-226 (Ra-226)
Radon-222 (Rn-222)
8
First source
Radium-226 (Ra-226)
9
Amount of radium substitute source that gives the same output as a 1 mg Ra source encapsulated in 0.5 mm platinum (Pt) in the same output measurement geometry
Milligram radium equivalent (mgRaeq)
10
Cesium-137 (Cs-137) clinical use
LDR intracavitary and interstitial
11
Cs-137 half life
30 years
12
Cobalt-60 (Co-60) dual and average energies
Dual: 1.17 MeV and 1.33 MeV
Average: 1.25 MeV
13
3 clinical uses of Co-60 and why
HDR intracavitary because it has a higher energy than other sources
Machine testing and calibration because it is known how much it decays
EBRT source because its Dmax is 0.5 cm
14
Co-60 Dmax
0.5 cm
15
2 prostate seed sources
Iodine-125 (I-125)
Palladium-103 (Pd-103)
16
Iodine-125 (I-125) half life
59.6 days
17
Palladium-103 (Pd-103) half life
17 days
18
2 brachytherapy (brachy) seed arrangements
Linear
Planar
19
How long the beam is on and how long it takes to deliver dose
Milligram-hour (mghr)
20
Mghr _______ with distance from source
Increases
21
2 source types
Point
Linear
22
4 HDR treatments
Breast
GYN
Prostate
Interstitial STS and esophageal
23
HDR "egg whisk" surgically inserted in seroma cavity of breast once a day for five days
Savi applicator
24
2 GYN HDR applicators
Vaginal cylinder
Tandem and ovoids (T&O): cervical
25
HDR prostate source
Iridium-192 (Ir-192)
26
1 mCi = ___ disintegration/sec
1 disintegration/sec
27
Activity after time (At) formula
At = Aoe^-(0.693/T1/2)(t)
Ao = original activity
T1/2 = half life
t = time
28
Rate between radium and current source
Exposure rate constant (Γ)
29
Γ unit
Rcm^2/mCihr
30
Exposure rate (X) follows _______
Inverse square law (ISL)
31
Exposure rate (X) formula
X = ΓA/r^2
r = radius/distance
32
Radium conversion/mgRaeq equation
Γ1A1 = Γ2A2
33
Number of seeds (n) equation
AL = n x s
AL = active length
s = s[acomg
34
Ovoids in _______, tandem in __________ (usually ___ dwell points
Fornices
Vaginal canal
3
35
T&O along distance at point 1, 2, 3, 4, and 5
1: 3
2: 1
3: 1
4: 3
5: 0
36
T&O away distance at point 1, 2, 3, 4, and 5
1: 2
2: 2
3: 2
4: 4
5: 3
37
How is an implant's effective area affected if both ends are closed, 1 is open, or 2/each end is open
Both: same as actual area
1 open: area reduced by 10% = (area)(0.9)
2 open: area reduced by another 10% = (area)(0.81)
38
3 ovoid sizes
2 cm
2.5
3 cm
39
Number of half lives (n) formula
(1/2)^n = At/Ao
40
3 dose rate classifications
HDR: 12 or more Gy/hr
MDR: 12-2 Gy/hr
LDR: under 2 Gy/hr
41
Parent's half life is much greater than the daughter's; ex: Ra (1626 yr) >> Rn (3.83 days)
Secular equilibrium
42
Parent's half life is slightly longer than daughter's; about 10 times
Ex: Mo-99 (67 hr) > Tc-99m (6.7 hr)
Transient equilibrium
43
Mean life (Ta) formula
Ta = 1.44(T1/2)
44
Technetium-99 clinical use
PET scan (transient equilibrium)
45
Brand name of radium (isotope) for bone mets, absorbed like calcium
Zofigo
46
Injection that mimics sugar uptake to see highly metabolic areas
False positive areas: brain, heart apex, bladder, etc.
Fludeoxyglucose (FDG-18)
47
Breast initial and boost dose
Initial: 45-50 Gy
Boost: 1000 cGy
48
Canadian breast protocol (higher daily dose and less total dose)
15 fractions x 287 cGy/day = 4005 cGy
49
Treatment time _______ as Co-60 decreases
Increases
50
Why do prostate sources usually have pointed ends?
To better stick to tissue
51
Why are brachy dose distributions usually anisotropic?
Usually more shielding on ends of source so more filtration on ends and isodoses closer to end
52
Non-isotropic, not equal in all directions
Anisotropic
53
Ra-226 half life
1626 years
54
Co-60 half life
5.26 years
55
I-131 half life
8.06 days
56
