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Board Revie > Brachytherapy > Flashcards

Brachytherapy Flashcards

1
Q

Half Life of Iodine-125

A

59.4 Days ( Tip: I-12(5) = (5)9.4 days)

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2
Q

Half Life of Palladium-103

A

17 days (Tip: Pd-(10)-(3)= 1(7) days)

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3
Q

Half life of Cs-131

A

9.6 Days (Tip: Cs-131 (1+1=2, 3^2) = (9).6 days)

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4
Q

Half Life of Co-60

A

5.26 years

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5
Q

Half Life of Cs-137

A

30 Years (Tip: Cs-1(3)7= (3)0 years)

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6
Q

Half life of Ir-192

A

73.8 Days (Tip: Ir-1(9)-(2)= (7)3.8 days)

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7
Q

Half Life of Ra-226

A

1622 years (Tip: Ra-226, inversion, 1(622) Years)

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8
Q

What three nuclides can be ordered as seeds, used as permanent implants and known to be “triplets”

A

I-125, Pd-103, Cs-131

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9
Q

What are the implant technique(s) for brachy?

A

Interstitial, Intracavitary, Intraluminal, Intravascular, Source Mold/Plaque

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10
Q

What are the treatment duration(s) of an implant?

A

Permanent or Temporary

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11
Q

What are the dose rates using in brachytherapy?

A

LDR, MDR, HDR, PDR

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12
Q

What are the ranges of the following Dose Rates in BT, LDR/MDR/HDR?

A

LDR (0.4-2 Gy/hr), MDR (2-12 Gy/hr), HDR (>12Gy/hr)

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13
Q

What dose rates in BT can be used for outpatient treatment?

A

HDR and LDR

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14
Q

What dose rates in BT can be used for inpatient treatment?

A

LDR

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15
Q

What are the techniques of loading an implant?

A

Preloaded BT, Manual Afterloading, Remote Afterloading

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16
Q

Explain the technique of Preloaded BT.

A

Source is loaded into applicator before patient treatment, then applicators placed into patient

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17
Q

Explain the technique of Manual Afterloading.

A

Applicator is placed into patient, then Clinician will manually place sources into applicator

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18
Q

Explain the technique of Remote afterloading.

A

Applicator is placed into patient, then machine will move the sources into the applicator (Less exposure and More accurate)

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19
Q

What are the patterns of source loading in BT?

A

Uniform and Non-uniform

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20
Q

Explain Uniform source loading.

A

All sources have the same activity or duration in the patient

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21
Q

Explain Non-uniform source loading.

A

All sources have different activity or durations vary with the patient

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22
Q

What is half-life simple defined as?

A

The amount of time it takes for half of the original activity to decay

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23
Q

If a radionuclide has a high half life (T1/2), what can be inferred about the decay constant for that radionuclide?

A

Half-life correlates to a small decay constant, as theoretically not a lot of decay is taking place

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24
Q

What is the average mean life defined as?

A
  • Time required for complete decay of PERMANENT sources
    -Used to Calculate Total Dose received from PERMANENT sources
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25
Q

What is activity equations relevance?

A

Can be used to calculate activity on different dates, or calculating specific activity at different times (past or future)

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26
Q

What are the two main classes of source strength specifications?

A

-Material Present (Mass of Radium and activity)
- Emitted Radiations output (Exposure rate and air-kerma strength)

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27
Q

What was used to define Curies for activity?

A

Mass of Radium

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28
Q

1 g Radium= ?

A

1 Ci=3.7x10^10 dps/bq

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29
Q

1 mg Radium =?

A

1 mg of Ci

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30
Q

What is the SI unit for activity?

A

1 Becquerel

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31
Q

Why can’t curie be applied to BT sources?

A

Distribution depends on ATTENUATION and SCATTERING of photons by encapsulated material. (BT is measured about what is outside the encapsulated material, Curie is the measurement of the source within)

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32
Q

What is defined to be Apparent Activity?

A

Acitivity of hypothetical UNFILTERED point source that has same exposure rate a calibration distance as source in question

33
Q

Explain mg-radium-equivalent (1mgRaEq)

A

Amount of radium substitute that has same output as 1 mg of radium source encapsulated in 0.5mm Pt

34
Q

1 Roentgen is equivalent to?

A

2.58 x 10^-4 C/kg

35
Q

What is exposure rates relationship to distance^2?

A

Doubling distance, will decrease exposure factor by 4

36
Q

Define Exposure rate Constant.

A

Exposure rate at a distance 1m from a point source of activity of 1 Ci

37
Q

What is the Exposure rate constant of Ra-226?

A

8.25 R-cm2/mCi-hr (mCi and mg are equal, so often time interchangeable) (Tip: this is with filtration from a 0.5mm Pt)

38
Q

For every ____ increase in thickness of platinum filtration, there is a _____ (decrease/increase) in the value.

A

0.1mm, 0.1 R-cm2/mg-h, Decrease (Tip: 8.25 value is already for 0.5mm filtration, so any increase after 0.5mm filtration is applicable)

39
Q

Define Air Kerma Strength and associated units.

A

Measure of energy transferred to air, U= cGy-cm^2/h

40
Q

What is Sk Calibration?

A

determination from exposure rate measured using a ion chamber in free air at a 1m.

41
Q

For Sk Calibration, what should be supplied?

A

Reentrant type well chamber or a dose calibrator with suitable standard source

42
Q

Explain directly traceable sources.

A

Sources calibrated in direct comparison with NIST or ADCL source of same kind (Same everything) (Tip: Calibration factor must be determined with compared source)

43
Q

What did the classical BT system encompass?

A
  • Models based on distribution about idealized point source
44
Q

What did the Quantitative BT system encompass?

A
  • Distributions measured by TLD/Diode
  • 3D Monte Carlo now acceptable and reliable
  • TG-43 were created to model source more accurately
45
Q

What concept do quantitative and classical system both support?

A

BT Source strength is to be specified as RADIATION OUTPUT IN FREE SPACE (Kerma rate, Dose rate, Exposure rate)

46
Q

In TG-43 Formalism, what does G(R,0) stand for and what does it account for?

A

Geometry Factor and accounts for geometric fall-off of photon fluence with distance

47
Q

In TG-43 Formalism, what does g(r) stand for and what does it account for?

A

Radial Dose Function and account for radial dependence of photon absorption and scatter along transverse axis

48
Q

In TG-43 Formalism, what does F(R,0) stand for and what does it account for?

A

Anisotropy Factor and accounts for angular dependence of photon absorption and scatter in the encapsulation

49
Q

What is the AAPM calibration recommendation for seeds to be assayed?

A

10 seed or 10% of total seeds, which ever is larger

50
Q

What is the most common LDR source and difference between HDR requirements?

A
  • Iodine-125 and Palladium-103
  • Low Energy
  • No room shielding
  • Placement is critical
51
Q

What is the most common HDR source and difference between LDR requirements?

A
  • Iridium 192
  • High Energy
  • Source NEVER leaves shielded area
  • Dosi more forgiving
52
Q

What is used to ensure the sources will be in the accurate position/applicator is in the correct positon?

A

Radiographs using dummy source or contrast from applicator

53
Q

What disadvantage of using manual afterloading?

A

Direct exposure to staff in direct care of patient

54
Q

What is the advantage of Remote afterloading?

A
  • Fast Dose falloff with distance
  • Computer drive source into applicator
55
Q

Explain the difference of defining absorbed dose to a point in an EBRT to a BT plan?

A

EBRT can use isocenter to represent dose to tumor, BT doesn’t have the capabilities to define a specific point as source placement will not be 100% in the same position, fast calcs are difficult to do and dose varies GREATLY within a region of sources

56
Q

Name the three interstitial Implant Dosimetry Systems.

A
  • Quimby/Memorial
  • Patterson-Parker/Manchester
  • Paris
57
Q

In all three systems, what is a common concept?

A

Defined therapeutic end points

58
Q

Explain the Patterson-Parker System.

A
  • “P,P= Periphery”
  • Maximize dose homogeneity INSIDE implanted volumes and treatment plane
  • Preferentially concentrates sources in PERIPHERY of implant
59
Q

Explain the Manchester System implant arrangements.

A
  • 1cm needles placed in Planar and volume arrangements with ends crossed with sources.
  • Full strength source in PERIPHERY and partial strength need CENTRALLY
60
Q

Define Point A.

A

2cm sup to cervical Os, and 2cm lateral to the midplane of patient

61
Q

What does point A represent?

A

Uterine vessels cross the ureter

62
Q

Define Point B

A

2 cm super to cervical Os and 5cm from midline of pelvic bony structure at

63
Q

What does point B represent?

A

Dose the lateral structures in the pelvis (Obturator nodes)

64
Q

When is Point A defined relative to the tandem and point relative to the mid line of the patient?

A

When applicator is NOT straight

65
Q

Of the three system for implant dosimetry, which is the most commonly used?

A

Patterson-Parker/Manchester

66
Q

What is the proportion of dose rate coming from Point A in relation to the Tandem and Ovoid

A

2/3 from Tandem and 1/3 Ovoids

67
Q

What is the portion of dose rate at Point A to Point B?

A

Point B is 1/3 the dose rate of Point A

68
Q

What dose ICRU-38 designate for BT treatments?

A

Dose be prescribed to a target volume instead of a point

69
Q

According ICRU-38, what is the maximum allowed dose the bladder and rectums for Gyn BT?

A

80% or less of the dose to Point A

70
Q

Treatment of Choice for early stage Endometrial CA?

A

Surgery or concurrent therapy (EBRT or BT)

71
Q

What dose is early stage Endometrial Cancer treated to with BT?

A

70Gy to 0.5cm depth

72
Q

What dose is advanced stage Endometrial Cancer treated to with BT?

A

75-90 Gy with EBRT and BT

73
Q

What dose is Vulvar Ca treated to?

A

70 Gy, with risk of fibrosis if exceeded

74
Q

What dose is Vaginal Ca treated to?

A
  • 60-70 Gy with BT alone
    -70-80 Gy with EBRT + BT
75
Q

What is the dose tolerance in Vaginal Ca treatment?

A

100Gy

76
Q

What Gyn organ is most radiosensitive?

A

Ovarians

77
Q

What Gyn organ is most radioresistant?

A

Uterine Canal

78
Q

For prostate cancer, what are treatment options for low to intermediate risk ?

A

Surveillance, Radical Prostatectomy and BT

79
Q

What two factors are related to Increase risk of catheter use and irritative urine morbidity?

A

IPSS (International Prostate Symptom Score) and Low Flow Max (Qmax)

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