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Dosimetry Physics 1 > Dose Calculations > Flashcards

Dose Calculations Flashcards

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1
Q

Where is SSD technique set at?

A

Patient skin, 100cm from the source, target

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2
Q

What dose calculation factors are used for SSD technique?

A

PDD and TMR

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3
Q

Where must the machine output be calibrated at for SSD technique?

A

SAD + Dmax

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4
Q

Where is SAD technique set at?

A

patients tumor or midline set at isocenter of 100cm from the source or target of the linac. (80cm for Cobalt-60 Machines)

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5
Q

What are the dose calculations utilized for SAD technique?

A

TAR, TMR, PDD

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6
Q

Where should the machine output be calibrated at for SAD technique?

A

Distance+ Depth= SAD (100cm SAD for Linac, 80cm SAD for Co-60)

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7
Q

What must be used when reference dose rates are not

calibrated for the right technique?

A

Inverse Square Correction Factor

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8
Q

Back Scatter Factor =

A

Dose @ Dmax in medium/Dose at same point in air

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9
Q

Back Scatter Factor

A
  • Dependent on the Beam Energy and Field Size

- Independent of SSD

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10
Q

Field Size Correction Factor for Co-60

A

The ratio of ionization at given field size at a point in air to a 10x10 field size at same point

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11
Q

Field Size Correction Factor Equation

A

Cfs= R(FS,80)/R(10x10,80)

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12
Q

What are some attenuation factors?

A

Tray factor, wedge factor

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13
Q

Cattn=

A

Dose with device/Dose without device

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14
Q

when you are given an MU/Timer calculation, with the following factor s (Dose rate given in air, SAD), which of the following will you use? TMR. TAR. PDD. TPR

A

TAR

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15
Q

when you are given an MU/Timer calculation, with the following factor s (Dose rate given in air, SSD), which of the following will you use? TMR. TAR. PDD. TPR

A

PDD

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16
Q

when you are given an MU/Timer calculation, with the following factor s (Dose rate given in Phantom, SAD), which of the following will you use? TMR. TAR. PDD. TPR

A

TMR

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17
Q

When you are given an MU/Timer calculation, with the following factor s (Dose rate given in Phantom, SSD), which of the following will you use? TMR. TAR. PDD. TPR

A

PDD

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18
Q

For Co-60 Machine, Dose rate @ Dmax =?

A

Dose/Time (cGy/Min)

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19
Q

For Co-60 machine, Total Dose rate @ Dmax= ?

A

Beam on-time x Dose rate at Dmax

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20
Q

For Co-60, Tumor dose @ depth =?

A

Dose Rate x PDD @ depth x Beam-on time

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21
Q

d stands for what in SAD technique?

A

Depth of target or depth of point of calculation

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22
Q

Tissue Air ratio=

A

Dp(r,o)/Da(r,d)

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23
Q

Tissue Air Ratio

A
  • used in calculations for rotational therapy
  • SSD may change in rotational therapy, however, SAD remains constant
  • TAR replaces PDD and BSF
  • Decreases with depth
  • is BSF at Dmax
  • TAR increases with increases in Field Size
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24
Q

What is the MU calculation formula for Co-60 Machine that has a 10x10 Field size and Isocenter in air calibration?

A

SSD:
Tumor Dose/(RDRx ISCFxBSFx(SSD/SSD+0.5)^2xPDD + Shuttle Error

SAD:
Tumor Dose/ (RDRxISCFxCattnxTAR) + Shuttle Error

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25
Q

What is Sc

A

Collimator Scatter Factor

26
Q

What occurs to Sc as Field Size increases?

A

Sc Increases

27
Q

What is Sp?

A

Phantom Scatter Factor

28
Q

What is Scp?

A

Total Scatter Factor

29
Q

Total Scatter Factor accounts for?

A

The changes in scatter radiation in the phantom and collimator at depth as field size changes

30
Q

Tissue Maximum Ratio

A
  • Independent of SSD

- Depends on Field Size and depth of the overlying tissue

31
Q

Sc is defined at? Sp is related to?

A

Sc is defined at SAD and Sp relates to the radiation field within the patient

32
Q

What is the MU Factor that is utilized for asymmetric fields? What are some important engineering behind asymmetric fields?

A
  • Jaws can move independently

- You could also position the field away from the central beam axis

33
Q

What does OAR stand for in MU Calculations

A

Off-axis ratio

34
Q

what is off-axis ratio

A

Ratio of dose at (x) cm off the central @ depth to dose at central axis @ same depth

35
Q

What Occurs to TMR as Field Size Increases?

A

Increase

36
Q

What occurs to PDD as depth decrease?

A

PDD increases

37
Q

What occurs TAR as Beam Energy increases?

A

TAR increase

38
Q

What occurs to PDD as SSD increases?

A

PDD increases

39
Q

What occurs to TMR and TPR as SSD increases?

A

No Change

40
Q

What occurs to TMR as Beam Energy decreases?

A

TMR decreases

41
Q

What occurs to PDD as Field Size decreases?

A

SSD decreases

42
Q

What occurs to TAR as Depth Increases?

A

TAR Decreases

43
Q

What occurs to PDD as beam energy increases?

A

PDD increases

44
Q

What occurs to TMR as Depth as decreases?

A

TMR decreases

45
Q

What occurs to TAR as field size decreases?

A

TAR decreases

46
Q

For TMR, field size is measured at?

A

Treatment SAD

47
Q

For TAR, machine output is measured at?

A

Treatment SAD

48
Q

For PDD, Machine output is measured at?

A

SSD + Dmax

49
Q

For TMR, Machine output is measured at?

A

Treatment SAD

50
Q

For TMR, field size is measured at?

A

Treatment SAD

51
Q

For PDD, field size is measured at?

A

On the skin

52
Q

Percent Depth Dose

A

percentage of absorbed dose at depth compared to the absorbed dose at Dmax

53
Q

Tissue Air Ratio

A

ratio of dose at given point in phantom to the dose in free space at the same point

54
Q

Tissue Phantom Ratio

A

the ratio of the dose at a given point at depth in phantom to the dose rate at the same point and distance at a reference depth

55
Q

Tissue Maximum Ratio

A

Ratio of dose at given point in phantom to dose at Dmax

56
Q

what is the other name for Collimator Scatter Factor?

A

In-air output ratio

57
Q

ISCF. Yuh or Nah?

  • SSD Technique
  • Machine output @ SAD
A

YUH

58
Q

ISCF. Yuh or Nah?

  • SAD Technique
  • Machine output @ SAD
A

NAH

59
Q

ISCF. Yuh or Nah?

  • SSD Technique
  • Machine output @ SSD + Dmax
A

NAH

60
Q

ISCF. Yuh or Nah?

  • SAD Technique
  • Machine output @ SSD + Dmax
A

YUH

61
Q

ISCF equation

A

(D1/D2)^2

Dosimetry Physics 1 (6 decks)

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