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Dosimetry Physics 1 > Dose Calculations > Flashcards

Dose Calculations Flashcards

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
What is Sc
Collimator Scatter Factor
26
What occurs to Sc as Field Size increases?
Sc Increases
27
What is Sp?
Phantom Scatter Factor
28
What is Scp?
Total Scatter Factor
29
Total Scatter Factor accounts for?
The changes in scatter radiation in the phantom and collimator at depth as field size changes
30
Tissue Maximum Ratio
- Independent of SSD | - Depends on Field Size and depth of the overlying tissue
31
Sc is defined at? Sp is related to?
Sc is defined at SAD and Sp relates to the radiation field within the patient
32
What is the MU Factor that is utilized for asymmetric fields? What are some important engineering behind asymmetric fields?
- Jaws can move independently | - You could also position the field away from the central beam axis
33
What does OAR stand for in MU Calculations
Off-axis ratio
34
what is off-axis ratio
Ratio of dose at (x) cm off the central @ depth to dose at central axis @ same depth
35
What Occurs to TMR as Field Size Increases?
Increase
36
What occurs to PDD as depth decrease?
PDD increases
37
What occurs TAR as Beam Energy increases?
TAR increase
38
What occurs to PDD as SSD increases?
PDD increases
39
What occurs to TMR and TPR as SSD increases?
No Change
40
What occurs to TMR as Beam Energy decreases?
TMR decreases
41
What occurs to PDD as Field Size decreases?
SSD decreases
42
What occurs to TAR as Depth Increases?
TAR Decreases
43
What occurs to PDD as beam energy increases?
PDD increases
44
What occurs to TMR as Depth as decreases?
TMR decreases
45
What occurs to TAR as field size decreases?
TAR decreases
46
For TMR, field size is measured at?
Treatment SAD
47
For TAR, machine output is measured at?
Treatment SAD
48
For PDD, Machine output is measured at?
SSD + Dmax
49
For TMR, Machine output is measured at?
Treatment SAD
50
For TMR, field size is measured at?
Treatment SAD
51
For PDD, field size is measured at?
On the skin
52
Percent Depth Dose
percentage of absorbed dose at depth compared to the absorbed dose at Dmax
53
Tissue Air Ratio
ratio of dose at given point in phantom to the dose in free space at the same point
54
Tissue Phantom Ratio
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
Tissue Maximum Ratio
Ratio of dose at given point in phantom to dose at Dmax
56
what is the other name for Collimator Scatter Factor?
In-air output ratio
57
ISCF. Yuh or Nah? - SSD Technique - Machine output @ SAD
YUH
58
ISCF. Yuh or Nah? - SAD Technique - Machine output @ SAD
NAH
59
ISCF. Yuh or Nah? - SSD Technique - Machine output @ SSD + Dmax
NAH
60
ISCF. Yuh or Nah? - SAD Technique - Machine output @ SSD + Dmax
YUH
61
ISCF equation
(D1/D2)^2

Dosimetry Physics 1 (6 decks)

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