2nd Year: Brachytherapy Numbers Flashcards
1
Q
What dose rates characterize HDR? Where is the dose rate specified?
A
12 Gy/hr at prescription point
2
Q
What dose rates characterize MDR? Where is the dose rate specified?
A
2 - 12 Gy/hr at prescription point
3
Q
What dose rates characterize LDR? Where is the dose rate specified?
A
0.4 - 2 Gy/hr at prescription point
4
Q
What is the typical initial dose rate for permanent implants at prescription point?
A
8 - 32 cGy/hr
5
Q
What two reports define the HDR, MDR and LDR dose rates?
A
ICRU38 and 10CFR35
6
Q
What is the exposure rate constant for Ra-226?
A
8.25 R cm2 / mCi hr
7
Q
What is the conversion of Ci to Bq?
A
1 Ci = 3.7 E10 Bq
8
Q
How many mCi are in 1 mg Ra Eq?
A
1 mCi = 1 mg Ra Eq
9
Q
What is a mg Ra Eq conceptually?
A
Equivalent source strength from radium with a 0.5 mm platinum encapsulation
10
Q
What is the half-life of Ir-192?
A
73.8 days
11
Q
What is the average energy of Ir-192?
A
397 keV (depending on filtration)
12
Q
What is the average HVL of Ir-192 (lead)
A
HVL = 2.5 mm Pb (depending on filtration)
13
Q
What is the exposure rate constant for Ir-192?
A
4.69 R cm2 / mCi hr
14
Q
What is the half-life of Co-60?
A
5.26 years
15
Q
What is the average photon energy of Co-60?
A
1.25 MeV
16
Q
What is the half-life of Cs-137?
A
30 years
17
Q
What is the average photon energy of Cs-137?
A
662 keV
18
Q
What is the half-life of I-125?
A
59.4 days
19
Q
What is the average photon energy of I-125?
A
28 keV
20
Q
What is the half-life of Pd-103?
A
17 days
21
Q
What is the average photon energy of Pd-103?
A
21 keV
22
Q
What is the exposure rate constant of Pd-103?
A
1.48 R cm2 / mCi hr
23
Q
What is the exposure rate constant of I-125?
A
1.46 R cm2 / mCi hr
24
Q
What two reactions does Ir-192 undergoe? Which is more probable?
A
Beta minus decay (95.1%) Electron capture (4.9%)
25
What is the half-life of Ra-226?
1622 years
26
What step size do we use for our HDRs?
0.3 cm
27
What is the first source position we use for our HDRs?
0.1 cm
28
What is the length of the channel used for segmented cylinders?
150 cm
29
What is the length of the channel used for T&O, T&C and T&R?
150 cm
30
What is the length of the channel used for endobronch applicator?
131 cm
31
What is the length of the interstitial prostate (collett) channels?
150 cm
32
What type of TGT is used for the vaginal cylinders?
Click-fit
33
What type of TGT is used for the interstitial prostates?
Yellow collett
34
Why for bravos do we use a 0.3 cm step size?
Because the active source length is 0.35 cm
Using a step size just below the active length size gives a nice dose distribution
35
What is a typical prescription for monotherapy HDR cylinder?
30 Gy in 5 Fx to the upper 1/3 of vaginal cuff, 0.5 cm depth
Twice weekly
Or 21 Gy in 3 Fx, 0.5 cm depth
36
What is the typical prescription for vaginal cylinder following 45 Gy of EBRT?
18 Gy in 3 Fx to the upper 1/3 of vaginal cuff twice weekly
or
11 Gy in 2 Fx to the upper 1/3 of vaginal cuff twice weekly
37
What is the typical prescription for prostate monotherapy HDR?
27 Gy in 2 Fx
Two weeks apart
38
What is the typical prescription for prostate EBRT + HDR Bst?
50 Gy EBRT + 13.5 or 14 or 15 Gy in 1 Fx HDR Bst
39
What is the rectum dose constraint that we use for prostate HDR?
Rectum V75% \< 1 cc
40
What is the bladder dose constraint that we use for prostate HDR?
V75% \< 1 cc
41
What is the urethra dose constraints that we use for prostate HDR?
Urethra Dmax \< 125%
42
What is the coverage criteria for prostate HDRs?
D90% \> 90% and \< 130%
and
D100% \> 10 Gy
and
V100% \> 98%
43
What are the prostate constraints in prostate HDRs?
V150% \< 50%
V200% \< 25%
44
What is a typical prescroption for HDR T&O?
5-6 Gy x 5 Fx following 45 Gy EBRT
Twice weekly
45
For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for the bladder?
D2cc \< 90 Gy
46
For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for the rectum?
D2cc \< 75 Gy
47
For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for the sigmoid?
D2cc \< 75 Gy
48
For T&O HDR, what is the Pt A goal?
prescription dose to Pt A
49
For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for the bowel?
D2cc \< 75 Gy
50
What is the relationship between air kerma strength and exposure rate?
SK = 0.876\*Exposure rate [cGy m2/hr]
51
What is the measurement volume of our well chamber?
245 cc
52
Approximately how long does the well chamber take to stabilize when connected to an electrometer?
10 minutes
53
Approximately how long should you keep the well chamber in the room for thermal equilibrium to be reached?
7 hours for a 4 celsius temperature difference
54
What bias is applied to a well-type chamber?
+- 300 V
55
For low energy photon emitting seeds, what is the approximate relationship between contained activity and apparent activity?
Contained activity = 1.6x apparent activity
56
What is the common active source length for Ir-192 sources (besides the one we use)
3.5 mm
57
What is typical endobronch prescription and prescription point?
5-6 (typically 6) Gy/fx for 3 fractions
1 cm from center of catheter (PTV eval expanded out)
58
What is the half-life of I-131?
8 days
59
What is the decay mode of I-131?
beta minus
Then how does it contribute dose to public?
The daughter, Xe-131, returns to ground state release photons
60
What is the typical administered activity for I-131 thyroid treatments?
30 - 300 mCi
61
What is the half-life of Y-90?
64.2 hours
62
What decay mode does Y-90 undergoe?
Purely beta emitter
63
What is the half-life of Lu-177?
6.73 days
64
What is the maximum energy of Lu-177 beta emitter?
497 keV
65
What is the maximum allowed lutathera exposure/dose rate at 1 meter for release in our clinic?
2.1 mR/hr (mrem/hr)
66
What is the typical prescription for Lutathera?
207 mCi per infusion, 4 infusions administered over the course of 1 year
1 month of lutathera, 1 month of somatostatin (substitute for chemo that slows down hormone release and helps shrink tumor), 1 month of rest
67
Per TG-59, what is the rule of thumb for dose received for 10 minute exposure at 10 cm from a 10 Ci HDR source?
0.75 Gy
68
Per TG-59, what is the rule of thumb for dose received for 10 minute exposure at 50 cm from a 10 Ci HDR source?
3 cGy
69
Per TG-59, what is the rule of thumb for dose received for 10 minute exposure at 1 m from a 10 Ci HDR source?
0.75 cGy
70
What is the limit for number of cycles that the source wire can extend and contract?
7000 cycles
71
What is the limit for number of cycles that the dummy wire can extend and contract?
15000 cycles
72
On average, approximately how many wire cycles occur in a given quarter for most afterloaders in most clinics?
Approximately 200 cycles per quarter
73
Approximately what fraction of total wire cycles are used to actually give treatment?
1/4 to 1/2 the total number of wire cycles
74
What is a typical prescription for IORT used in breast cancer for...
Negative or close margins
Positive margins
Grodd residual margins or unresectable tumor
Negative or close margins: 7.5 - 10 Gy
Positive margins: 10 - 12.5 Gy
Gross residual amrgins: 15 - 20 Gy
All of these are delivered after EBRT
All of these are 1 fraction
75
What is typical treatment length of a Zeiss Intrabeam IORT procedure?
15 - 20 minutes
76
How much additional shielding is needed for OR's in which Zeiss Intrabeam IORT is commonly performed?
Trick question, none is needed
Radiation is low kV and is already mostly attenuated by the patient. What makes it to the pre-existing wall is already very low
77
What is the typical prescription point, and dose to point for a Zeiss Intrabeam?
20 Gy at applicator surface
Dose at 1 cm depth varies depending on applicator size, but is typically 5 Gy
78
For surface HDR, what is the typical prescription depth?
0.5 cm
79
For IOERT, what margin is given around the tumor site?
1 cm
80
What is the typical dose rate of a Mobetron? What are typical energies?
10 Gy/min
6,9,12 MeV electrons
81
For Zeiss Intrabeam IORT for breasts, what was the operating voltage we used to use?
50 kVp
82
After performing specific QA for a Zeiss INTRABEAM system, how long is the QA valid for?
36 hours
83
By approximately what factor does shielding in the Zeiss INTRABEAM probe system reduce dose rate to otherside?
Cuts dose rate roughly in half
0. 5 mR/hr (behind shield)
1. 2 mR/hr (in front of shield)
84
How many sterilization cycles are the Zeiss spherical applicators good up to?
100 cycles
85
What is the approximate exposure per second 1 meter from the Ir-192 source in air?
1 mr/sec at 1 meter away
86
For model based vs TG-43 protocols, what is the approximate dose difference for high energy sources for PTV coverage and dose to bone
About 5%
87
For model based dose calculation algorithms, what is the modeling accuracy that must be achieved when modeling the seed and applicators?
1 micrometer resolution
88
What is the typical prostate LDR prescription for I-125 seeds?
145 Gy
89
What is the typical prostate LDR prescription for Pd-103 seeds?
125 Gy
90
What is the typical prostate LDR prescription for Cs-131 seeds?
115 Gy
91
What is the tolerance for source location TPS vs measured?
1 mm
92
What is the historical prescription of a permanent mesh lung implant?
100 Gy to 5 mm depth from plane of mesh
93
What is the typical prescription for intravascular brachytherapy?
15 - 20 Gy prescribed to 0.5 - 2 mm from source (or 2 mm beyond lumen radius) treated along 2-5 cm length of artery
94
What is the typical dose rate for LDR radioactive stents for intravascular brachytherapy? What about HDR?
LDR: 1 - 5 cGy/hr
HDR: Gy/minute
95
What is the prescription of eye plaques?
85 Gy to water at a depth of 5 mm if apex height is \< 5 mm, or to apex heigh if height is \> 5 mm
96
What is the typical implant time for a eye plaque?
3 - 12 days. Most commonly 3 or **4 days (96 hrs)**
97
What is the typical eye plaque dose rate?
0.6 - 1.25 Gy/hr
98
What is the maximum operating temperature of the axxent electronic brachytherapy system apparatus surface?
40 celsius
99
For LDR prostates, how is PTV defined?
Prostate + 3 mm margin
100
What is typical LDR doses for LDR prostate boost following EBRT with I-125?
110 Gy
101
What is typical LDR doses for LDR prostate boost following EBRT with Pd-103?
90-100 Gy
102
What α/β is used for prostate in most publications?
2
103
What is the average half-life of edema caused by LDR prostate seed implants?
9.3 days
104
How many needles are typically used for interstitial prostate HDR?
15 - 25
105
What is a less commonly used, but still possible HDR prostate prescription?
Monotherapy: 9 Gy x 4 Fx (BID, 4 hours minimum)
Boost: 8.5 Gy x 2 (BID, 4 hours)
106
In prostate LDR, what is the typical amount of seeds that are commonly used?
45 - 75 (at most, 100)
107
What slice thickness is used for all brachytherapy planning in our clinic?
0.625 mm
108
What is the SFOV used for all brachytherapy planning in our clinic?
\< 50 cm
109
What is the nominal length of a collett TGT used for HDR prostate?
125.6 cm
110
What is the combined T&O + EBRT EQD2 dose to HR-CTV?
80 - 85 Gy EQD2
111
What is the combined vaginal cylinder + EBRT EQD2 dose to vaginal mucosa?
75 - 80 Gy EQD2
112
What is the ABS accelerated partial breast irradiation prescription? Include prescription point
3.4 Gy x 10 Fx, twice daily, 6 hour separation, 5 days, prescribed to 1 cm annulus around applicator
113
For accelerated partial breast irradiation using balloon catheter, what is the maximum allowable seroma that can be present?
Volume of air/seroma not to exceed 10% of volume of PTV\_Eval
114
What is the target coverage requirement in APBI?
V90% \> 95%
Remember: This is for PTV\_Eval
115
In APBI, what is the maximum dose constraint to ribs/chestwall and skin
Ribs/Chestwall: Dmax \< 125%
Skin: Dmax \< 100%
116
How long is a typical APBI MammoSite procedure with a 10 Ci source?
5 - 6 minutes
117
What are typical scan parameters for HDR APBI?
0.625 slice thickness with \< 15 cm SFOV for good resolution
118
What skin thickness is used for APBI to contour the skin critical structure?
5 mm
119
When calc'ing 3D dose in brachytherapy what calc grid size is used?
1 mm or less
120
What is the typical endobronch prescription?
5 or 6 Gy/fx in 3 Fx prescribed to 1 cm from center of catheter (PTV eval expanded out)
121
What is the dose coverage goal in endobronch?
100% of volume covered by 100% of the dose
122
Per the ICRU 89 (updated Manchester system), what should Pt A, bladder and rectum point doses be?
Pt A gets prescription dose
Bladder point dose \< 80% of prescription
Rectum point dose \< 80% of prescription
123
What is the prescription for LDR T&O monotherapy? Which isotope is used?
Two, 48 hour insertions at 31.5 Gy each
Separated by 2 weeks
Cs-137
124
What is the prescription for LDR T&O as a boost to EBRT?
Two, 48-hour insertions at 20 Gy each,
separated by 2 weeks
Cs-137
125
Up to what distance away from a Ir-192 source does inverse square effects dominate?
3 cm
126
What is the appropriate rule of thumb to convert from LDR doses to HDR doses?
LDR dose \* 0.6 to 0.7 = HDR dose
127
Per TG-137, What is the rectum dose constraint for LDR prostate brachytherapy?
**D2cc \< 100%**
D0.1cc \< 150%
128
Per TG-137, What is the urethra dose constraint for LDR prostate brachytherapy?
D10% \< 150%
D30% \< 130%
129
Per TG-137, What is prostate coverage in LDR constraint?
**V100% \> 95%**
D90% \> 100%
130
What is the approximate order of magnitude activity per seed for LDR prostate seeds?
~ half a mCi
131
What is the Roentgen to rad conversion factor for air?
0.876 rad/R
or
0.876 cGy/R
132
How much is 1 mg Ra Eq in R/hr?
8.25 x 10-4 R/h
133
What are the typical dimensions of an Ir-192 source?
0.3 to 0.6 mm in diameter, and 3.5 to 10 mm in length
134
What are the typical dimensions of an Ir-192 source?
0.3 to 0.6 mm in diameter, and 3.5 to 10 mm in length
135
What is typical **max** diameter and volume of contrast for APBI ballooms?
4 - 6 cm with 25 - 125 cc contrast liquid
For ellipsoidal, 4 x 6 cm with 65 cc of contrast
136
Approximately what fraction is the dose to Pt B relative to pt A?
25%
137
What is typical activity of an individual seed for I-125 LDR prostate?
0.3 - 0.5 mCi
138
What is the V90 dose constraint for APBI for Interstitial, Mammosite and SAVI?
For all 3 of them,
V90 \> 90%
139
What is the target hot spot dose constraint (V150) for APBI for Interstitial, Mammosite and SAVI?
Interstitial: V150 \< 70 cc
SAVI and Mammosite: V150 \< 50 cc
140
What is the target hot spot dose constraint (V200) for APBI for interstitial, mammosite and SAVI?
Interstitial and SAVI: V200 \< 20 cc
Mammosite: V200 \< 10 cc
141
What is the general dose rate at 1 meter release value used for prostate seed implants?
1 mR/hr (mrem/hr)
142
What is the NRC limit on leakage levels for HDR afterloader units?
1 mR/hr at 10 cm from any surface of the afterloader
143
Per NSABP B-39, for single channel APBI, what is the minimum distance between applicator and skin allowed for treatment? What is the maximum dose constraint?
What about for multi-channel APBI?
**Single channel:**
balloon to skin distance \> 7 mm
skin max dose \< 145%
**Multi channel:**
Balloon to skin distance \> 5 mm
skin max dose \< 125%
**Fun fact:** These exact same values are also applicable to the chestwall per NSABP B-39
144
What is the value of 1 U?
1 U = 1 cGy cm2 / hr
