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ABR Part III > TG51 > Flashcards

TG51 Flashcards

1
Q

What are the 4 correction factors for photon calculations with TG51?

A

Pelec - electrometer correction factor for the electrometer calibration
Ptp - temperature and pressure correction factor correcting for the amount of mass actually in the chamber at the time of measurement
Pion - ion recombination correction factor to correct for ion pairs that were created but not collected
Ppol - polarity correction factor to correct for differences in collection based on the polarity of the chamber

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2
Q

How do you calculate Ptp?

A

Ptp = (273.2+T)/(273.2+22)*(760/P) - for a pressure measured in mmHg

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3
Q

How do you convert between kPa and mmHg?

A

1 kPa = 7.5 mmHg

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4
Q

How do you calculate Ppol?

A

Ppol = abs(Mraw+ - Mraw-)/2Mraw

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5
Q

What is a reasonable range for Ppol?

A

within 0.3% - 0.997 to 1.003

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6
Q

At what point should you be concerned about Pion and what should you do?

A

if Pion > 1.05, use a different chamber

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7
Q

At what point should you be concerned about Pion and what should you do?

A

if Pion > 1.05, use a different chamber

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8
Q

How do VH and VL relate when measuring Pion?

A

VL must be at least a factor of 2 less than VH.

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9
Q

How do you calculate Pion for pulsed/swept beams?

A

Pion = (1-VH/VL)/(MH/HM - VH/VL)

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10
Q

How do you calculate Pgrad for electron calculations?

A

Pgrad = M(dref + 0.5 rcav)/M(dref)

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11
Q

How big does your water tank need to be for a TG51 measurement?

A

at least 30 x 30 x 30 cm^3

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12
Q

What is dref in an electron beam?

A

dref = 0.6*R50 - 0.1 where dref is in cm.

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13
Q

How thick of a lead foil should be used for a TG51 measurement in a high-energy beam?

A

1 mm (+/- 20%)

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14
Q

Which energy beams should use a lead foil for a TG51 measurement?

A

all FFF beams (and 10 MV+ but addendum says no)

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15
Q

At what distance should the lead foil be from the phantom surface for a TG51 measurement?

A

~50 cm (+/- 5 cm), or 30cm +/- 1 cm if 50cm is not possible

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16
Q

What is Pgrad for a parallel plate chamber?

A

1

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17
Q

What is Qecal for a TG51 measurement?

A

arbitrary electron beam quality of R50 = 7.5 cm

18
Q

What is the reference field size for electron TG51 measurements?

A

> = 10x10 unless R50 > 8.5 cm (E > 20 MeV), then >=20x20

19
Q

What is the TG51 equation for photons beams?

A

D = MKqND,w,Co-60

20
Q

What is the TG51 equation for electron beams?

A

D = MPQgradk’R50kecalND,W,Co-60

21
Q

How long should you wait for your chamber to reach thermal equilibrium with water in a water tank?

A

5-10 min

22
Q

What is the assumed range of humidity and what uncertainty does that introduce into a TG51 calculation?

A

20-80%, 0.15%

23
Q

What SSD must your PDD be taken in when determining your beam quality for TG51?

A

100

24
Q

Where is your effective point of measurement in a cylindrical chamber in a photon beam?

A

0.6*rcav upstream

25
Q

Where is your effective point of measurement in a cylindrical chamber in an electron beam?

A

0.5*rcav upstream

26
Q

What is the reference depth for TG51 photon beam measurements?

A

10 cm

27
Q

How do you find Kq if your chamber isn’t on the table?

A

closest match by:
1) wall material 2) radius of air cavity 3) electrode material 4) wall thickness

28
Q

What is the volume of a farmer chamber?

A

0.6 cc

29
Q

What is a typical farmer chamber radius?

A

3 mm

30
Q

What is a typical farmer chamber length?

A

~2 cm

31
Q

What is the limit on the magnitude of Pleak in TG51 addendum?

A

Should be <= 0.1%, anything above 0.5% must be investigated

32
Q

What is the purpose of Prp in TG51 addendum?

A

To take into account off-axis variation in the intensity profile across the active volume of the chamber.

33
Q

What energies does TG51 apply to?

A

Co60 - 50 MV photon beams and 4 to 50 MeV electron beams

34
Q

What is kQ for electron beams in TG51?

A

kQ = PQgrad * kR50

35
Q

What is kR50 for electron beams in TG51?

A

kR50 = kR50’ * kecal

36
Q

At what wall thickness do you need to correct measurements through the wall for the effective depth of measurement in a TG51 measurement??

A

thickness > 0.2 cm

37
Q

How do you calculate the effective thickness of PMMA?

A

physical thickness * 1.12

38
Q

What theory is kq dependent on in TG51?

A

Spencer-Attix cavity theory

39
Q

How sensitive is kQ to changes in PDD10x?

A

1% change in PDD10x is a 0.1% change in kQ - therefore, the largest uncertainty in kQ is likely in picking the right curve and interpolating to your quality

40
Q

How much uncertainty is introduced by measuring without a lead foil in higher energy beams?

A

0.2%

41
Q

How much can your calibration coefficient change over the 2-year calibration span?

A

<0.3%

42
Q

How much can your chamber reading change from first irradiation to stabilization?

A

<0.5%/MU

ABR Part III (13 decks)

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