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Residency > 2nd Year: Brachytherapy Numbers > Flashcards

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

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2
Q

What dose rates characterize MDR? Where is the dose rate specified?

A

2 - 12 Gy/hr at prescription point

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3
Q

What dose rates characterize LDR? Where is the dose rate specified?

A

0.4 - 2 Gy/hr at prescription point

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4
Q

What is the typical initial dose rate for permanent implants at prescription point?

A

8 - 32 cGy/hr

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5
Q

What two reports define the HDR, MDR and LDR dose rates?

A

ICRU38 and 10CFR35

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6
Q

What is the exposure rate constant for Ra-226?

A

8.25 R cm2 / mCi hr

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7
Q

What is the conversion of Ci to Bq?

A

1 Ci = 3.7 E10 Bq

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8
Q

How many mCi are in 1 mg Ra Eq?

A

1 mCi = 1 mg Ra Eq

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9
Q

What is a mg Ra Eq conceptually?

A

Equivalent source strength from radium with a 0.5 mm platinum encapsulation

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10
Q

What is the half-life of Ir-192?

A

73.8 days

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11
Q

What is the average energy of Ir-192?

A

397 keV (depending on filtration)

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12
Q

What is the average HVL of Ir-192 (lead)

A

HVL = 2.5 mm Pb (depending on filtration)

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13
Q

What is the exposure rate constant for Ir-192?

A

4.69 R cm2 / mCi hr

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14
Q

What is the half-life of Co-60?

A

5.26 years

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15
Q

What is the average photon energy of Co-60?

A

1.25 MeV

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16
Q

What is the half-life of Cs-137?

A

30 years

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17
Q

What is the average photon energy of Cs-137?

A

662 keV

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18
Q

What is the half-life of I-125?

A

59.4 days

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19
Q

What is the average photon energy of I-125?

A

28 keV

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20
Q

What is the half-life of Pd-103?

A

17 days

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21
Q

What is the average photon energy of Pd-103?

A

21 keV

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22
Q

What is the exposure rate constant of Pd-103?

A

1.48 R cm2 / mCi hr

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23
Q

What is the exposure rate constant of I-125?

A

1.46 R cm2 / mCi hr

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24
Q

What two reactions does Ir-192 undergoe? Which is more probable?

A 
Beta minus decay (95.1%) 
Electron capture (4.9%)
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25
Q

What is the half-life of Ra-226?

A

1622 years

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26
Q

What step size do we use for our HDRs?

A

0.3 cm

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27
Q

What is the first source position we use for our HDRs?

A

0.1 cm

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28
Q

What is the length of the channel used for segmented cylinders?

A

150 cm

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29
Q

What is the length of the channel used for T&O, T&C and T&R?

A

150 cm

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30
Q

What is the length of the channel used for endobronch applicator?

A

131 cm

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31
Q

What is the length of the interstitial prostate (collett) channels?

A

150 cm

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32
Q

What type of TGT is used for the vaginal cylinders?

A

Click-fit

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33
Q

What type of TGT is used for the interstitial prostates?

A

Yellow collett

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34
Q

Why for bravos do we use a 0.3 cm step size?

A

Because the active source length is 0.35 cm

Using a step size just below the active length size gives a nice dose distribution

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35
Q

What is a typical prescription for monotherapy HDR cylinder?

A

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

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36
Q

What is the typical prescription for vaginal cylinder following 45 Gy of EBRT?

A

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

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37
Q

What is the typical prescription for prostate monotherapy HDR?

A

27 Gy in 2 Fx

Two weeks apart

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38
Q

What is the typical prescription for prostate EBRT + HDR Bst?

A

50 Gy EBRT + 13.5 or 14 or 15 Gy in 1 Fx HDR Bst

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39
Q

What is the rectum dose constraint that we use for prostate HDR?

A

Rectum V75% < 1 cc

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40
Q

What is the bladder dose constraint that we use for prostate HDR?

A

V75% < 1 cc

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41
Q

What is the urethra dose constraints that we use for prostate HDR?

A

Urethra Dmax < 125%

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42
Q

What is the coverage criteria for prostate HDRs?

A

D90% > 90% and < 130%

and

D100% > 10 Gy

and

V100% > 98%

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43
Q

What are the prostate constraints in prostate HDRs?

A

V150% < 50%

V200% < 25%

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44
Q

What is a typical prescroption for HDR T&O?

A

5-6 Gy x 5 Fx following 45 Gy EBRT

Twice weekly

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45
Q

For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for the bladder?

A

D2cc < 90 Gy

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46
Q

For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for the rectum?

A

D2cc < 75 Gy

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47
Q

For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for the sigmoid?

A

D2cc < 75 Gy

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48
Q

For T&O HDR, what is the Pt A goal?

A

prescription dose to Pt A

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49
Q

For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for the bowel?

A

D2cc < 75 Gy

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50
Q

What is the relationship between air kerma strength and exposure rate?

A

SK = 0.876*Exposure rate [cGy m2/hr]

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51
Q

What is the measurement volume of our well chamber?

A

245 cc

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52
Q

Approximately how long does the well chamber take to stabilize when connected to an electrometer?

A

10 minutes

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53
Q

Approximately how long should you keep the well chamber in the room for thermal equilibrium to be reached?

A

7 hours for a 4 celsius temperature difference

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54
Q

What bias is applied to a well-type chamber?

A

+- 300 V

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55
Q

For low energy photon emitting seeds, what is the approximate relationship between contained activity and apparent activity?

A

Contained activity = 1.6x apparent activity

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56
Q

What is the common active source length for Ir-192 sources (besides the one we use)

A

3.5 mm

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57
Q

What is typical endobronch prescription and prescription point?

A

5-6 (typically 6) Gy/fx for 3 fractions

1 cm from center of catheter (PTV eval expanded out)

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58
Q

What is the half-life of I-131?

A

8 days

59
Q

What is the decay mode of I-131?

A

beta minus

Then how does it contribute dose to public?

The daughter, Xe-131, returns to ground state release photons

60
Q

What is the typical administered activity for I-131 thyroid treatments?

A

30 - 300 mCi

61
Q

What is the half-life of Y-90?

A

64.2 hours

62
Q

What decay mode does Y-90 undergoe?

A

Purely beta emitter

63
Q

What is the half-life of Lu-177?

A

6.73 days

64
Q

What is the maximum energy of Lu-177 beta emitter?

A

497 keV

65
Q

What is the maximum allowed lutathera exposure/dose rate at 1 meter for release in our clinic?

A

2.1 mR/hr (mrem/hr)

66
Q

What is the typical prescription for Lutathera?

A

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
Q

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?

A

0.75 Gy

68
Q

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?

A

3 cGy

69
Q

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?

A

0.75 cGy

70
Q

What is the limit for number of cycles that the source wire can extend and contract?

A

7000 cycles

71
Q

What is the limit for number of cycles that the dummy wire can extend and contract?

A

15000 cycles

72
Q

On average, approximately how many wire cycles occur in a given quarter for most afterloaders in most clinics?

A

Approximately 200 cycles per quarter

73
Q

Approximately what fraction of total wire cycles are used to actually give treatment?

A

1/4 to 1/2 the total number of wire cycles

74
Q

What is a typical prescription for IORT used in breast cancer for…

Negative or close margins

Positive margins

Grodd residual margins or unresectable tumor

A

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
Q

What is typical treatment length of a Zeiss Intrabeam IORT procedure?

A

15 - 20 minutes

76
Q

How much additional shielding is needed for OR’s in which Zeiss Intrabeam IORT is commonly performed?

A

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
Q

What is the typical prescription point, and dose to point for a Zeiss Intrabeam?

A

20 Gy at applicator surface

Dose at 1 cm depth varies depending on applicator size, but is typically 5 Gy

78
Q

For surface HDR, what is the typical prescription depth?

A

0.5 cm

79
Q

For IOERT, what margin is given around the tumor site?

A

1 cm

80
Q

What is the typical dose rate of a Mobetron? What are typical energies?

A

10 Gy/min

6,9,12 MeV electrons

81
Q

For Zeiss Intrabeam IORT for breasts, what was the operating voltage we used to use?

A

50 kVp

82
Q

After performing specific QA for a Zeiss INTRABEAM system, how long is the QA valid for?

A

36 hours

83
Q

By approximately what factor does shielding in the Zeiss INTRABEAM probe system reduce dose rate to otherside?

A

Cuts dose rate roughly in half

  1. 5 mR/hr (behind shield)
  2. 2 mR/hr (in front of shield)
84
Q

How many sterilization cycles are the Zeiss spherical applicators good up to?

A

100 cycles

85
Q

What is the approximate exposure per second 1 meter from the Ir-192 source in air?

A

1 mr/sec at 1 meter away

86
Q

For model based vs TG-43 protocols, what is the approximate dose difference for high energy sources for PTV coverage and dose to bone

A

About 5%

87
Q

For model based dose calculation algorithms, what is the modeling accuracy that must be achieved when modeling the seed and applicators?

A

1 micrometer resolution

88
Q

What is the typical prostate LDR prescription for I-125 seeds?

A

145 Gy

89
Q

What is the typical prostate LDR prescription for Pd-103 seeds?

A

125 Gy

90
Q

What is the typical prostate LDR prescription for Cs-131 seeds?

A

115 Gy

91
Q

What is the tolerance for source location TPS vs measured?

A

1 mm

92
Q

What is the historical prescription of a permanent mesh lung implant?

A

100 Gy to 5 mm depth from plane of mesh

93
Q

What is the typical prescription for intravascular brachytherapy?

A

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
Q

What is the typical dose rate for LDR radioactive stents for intravascular brachytherapy? What about HDR?

A

LDR: 1 - 5 cGy/hr

HDR: Gy/minute

95
Q

What is the prescription of eye plaques?

A

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
Q

What is the typical implant time for a eye plaque?

A

3 - 12 days. Most commonly 3 or 4 days (96 hrs)

97
Q

What is the typical eye plaque dose rate?

A

0.6 - 1.25 Gy/hr

98
Q

What is the maximum operating temperature of the axxent electronic brachytherapy system apparatus surface?

A

40 celsius

99
Q

For LDR prostates, how is PTV defined?

A

Prostate + 3 mm margin

100
Q

What is typical LDR doses for LDR prostate boost following EBRT with I-125?

A

110 Gy

101
Q

What is typical LDR doses for LDR prostate boost following EBRT with Pd-103?

A

90-100 Gy

102
Q

What α/β is used for prostate in most publications?

A

2

103
Q

What is the average half-life of edema caused by LDR prostate seed implants?

A

9.3 days

104
Q

How many needles are typically used for interstitial prostate HDR?

A

15 - 25

105
Q

What is a less commonly used, but still possible HDR prostate prescription?

A

Monotherapy: 9 Gy x 4 Fx (BID, 4 hours minimum)

Boost: 8.5 Gy x 2 (BID, 4 hours)

106
Q

In prostate LDR, what is the typical amount of seeds that are commonly used?

A

45 - 75 (at most, 100)

107
Q

What slice thickness is used for all brachytherapy planning in our clinic?

A

0.625 mm

108
Q

What is the SFOV used for all brachytherapy planning in our clinic?

A

< 50 cm

109
Q

What is the nominal length of a collett TGT used for HDR prostate?

A

125.6 cm

110
Q

What is the combined T&O + EBRT EQD2 dose to HR-CTV?

A

80 - 85 Gy EQD2

111
Q

What is the combined vaginal cylinder + EBRT EQD2 dose to vaginal mucosa?

A

75 - 80 Gy EQD2

112
Q

What is the ABS accelerated partial breast irradiation prescription? Include prescription point

A

3.4 Gy x 10 Fx, twice daily, 6 hour separation, 5 days, prescribed to 1 cm annulus around applicator

113
Q

For accelerated partial breast irradiation using balloon catheter, what is the maximum allowable seroma that can be present?

A

Volume of air/seroma not to exceed 10% of volume of PTV_Eval

114
Q

What is the target coverage requirement in APBI?

A

V90% > 95%

Remember: This is for PTV_Eval

115
Q

In APBI, what is the maximum dose constraint to ribs/chestwall and skin

A

Ribs/Chestwall: Dmax < 125%

Skin: Dmax < 100%

116
Q

How long is a typical APBI MammoSite procedure with a 10 Ci source?

A

5 - 6 minutes

117
Q

What are typical scan parameters for HDR APBI?

A

0.625 slice thickness with < 15 cm SFOV for good resolution

118
Q

What skin thickness is used for APBI to contour the skin critical structure?

A

5 mm

119
Q

When calc’ing 3D dose in brachytherapy what calc grid size is used?

A

1 mm or less

120
Q

What is the typical endobronch prescription?

A

5 or 6 Gy/fx in 3 Fx prescribed to 1 cm from center of catheter (PTV eval expanded out)

121
Q

What is the dose coverage goal in endobronch?

A

100% of volume covered by 100% of the dose

122
Q

Per the ICRU 89 (updated Manchester system), what should Pt A, bladder and rectum point doses be?

A

Pt A gets prescription dose

Bladder point dose < 80% of prescription

Rectum point dose < 80% of prescription

123
Q

What is the prescription for LDR T&O monotherapy? Which isotope is used?

A

Two, 48 hour insertions at 31.5 Gy each

Separated by 2 weeks

Cs-137

124
Q

What is the prescription for LDR T&O as a boost to EBRT?

A

Two, 48-hour insertions at 20 Gy each,

separated by 2 weeks

Cs-137

125
Q

Up to what distance away from a Ir-192 source does inverse square effects dominate?

A

3 cm

126
Q

What is the appropriate rule of thumb to convert from LDR doses to HDR doses?

A

LDR dose * 0.6 to 0.7 = HDR dose

127
Q

Per TG-137, What is the rectum dose constraint for LDR prostate brachytherapy?

A

D2cc < 100%

D0.1cc < 150%

128
Q

Per TG-137, What is the urethra dose constraint for LDR prostate brachytherapy?

A

D10% < 150%

D30% < 130%

129
Q

Per TG-137, What is prostate coverage in LDR constraint?

A

V100% > 95%

D90% > 100%

130
Q

What is the approximate order of magnitude activity per seed for LDR prostate seeds?

A

~ half a mCi

131
Q

What is the Roentgen to rad conversion factor for air?

A

0.876 rad/R

or

0.876 cGy/R

132
Q

How much is 1 mg Ra Eq in R/hr?

A

8.25 x 10-4 R/h

133
Q

What are the typical dimensions of an Ir-192 source?

A

0.3 to 0.6 mm in diameter, and 3.5 to 10 mm in length

134
Q

What are the typical dimensions of an Ir-192 source?

A

0.3 to 0.6 mm in diameter, and 3.5 to 10 mm in length

135
Q

What is typical max diameter and volume of contrast for APBI ballooms?

A

4 - 6 cm with 25 - 125 cc contrast liquid

For ellipsoidal, 4 x 6 cm with 65 cc of contrast

136
Q

Approximately what fraction is the dose to Pt B relative to pt A?

A

25%

137
Q

What is typical activity of an individual seed for I-125 LDR prostate?

A

0.3 - 0.5 mCi

138
Q

What is the V90 dose constraint for APBI for Interstitial, Mammosite and SAVI?

A

For all 3 of them,

V90 > 90%

139
Q

What is the target hot spot dose constraint (V150) for APBI for Interstitial, Mammosite and SAVI?

A

Interstitial: V150 < 70 cc

SAVI and Mammosite: V150 < 50 cc

140
Q

What is the target hot spot dose constraint (V200) for APBI for interstitial, mammosite and SAVI?

A

Interstitial and SAVI: V200 < 20 cc

Mammosite: V200 < 10 cc

141
Q

What is the general dose rate at 1 meter release value used for prostate seed implants?

A

1 mR/hr (mrem/hr)

142
Q

What is the NRC limit on leakage levels for HDR afterloader units?

A

1 mR/hr at 10 cm from any surface of the afterloader

143
Q

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?

A

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
Q

What is the value of 1 U?

A

1 U = 1 cGy cm2 / hr

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