TAR TMR Flashcards
The TAR at dmax on the CAX of the beam is referred to as what?
BSF (BACK SCATTER FACTOR)
The region between the patient’s skin and dmax is referred to as what?
Dose Build-up Region
The absorbed dose at a given depth expressed as a % of the absorbed dose at a reference depth (i.e. d-max) on the CAX of the field
PDD
PDD is dependent on what 5 variables?
- Energy
- Field Size
- SSD
- Depth
- Composition of the irradiated medium
Does PDD increase or decrease with increasing SSD?
Increase
Does PDD increase or decrease with increasing field size?
Increase
Does PDD increase or decrease with increasing depth?
Decrease
What is dose in tissue / dose at d-max in a phantom?
TMR
What 3 factors is TMR dependent on?
- Depth
- Energy
- Field Size
What is used to calculate changes in PDD?
Mayneord’s Factor
What is dose in tissue / dose in air?
TAR
Ratio of dose on the CAX at d-max to dose at the same point in air(dose at d-max / dose in air)
BSF (Back Scatter Factor)
BSF and _____ at Dmax are the same.
TAR
Is TMR dependent on SSD?
No
Which of the following is true when measuring Percent Depth Dose (PDD)?
A. The Source to Chamber distance is constant.
B. The chamber to Axis distance is constant.
C. The Source to Surface distance is constant.
D. The chamber depth is constant.
C. The Source to Surface distance is constant.
Which of the following is most often used to measure beam quality of a megavoltage photon beam? A. PDD at 10 cm B. TPR ratio at 20cm and 10 cm C. Half Value Layer D. Depth where PDD is 50% E. a and b only.
E. a and b only.
If the PDD at 10 cm is 80% at 100 cm SSD, what would the PDD be at 10 cm if the SSD is changed to 80 cm? (dmax = 3.0 cm)
Use Mayneord Factor
77.6
At approximately what energy does the Backscatter Factor become no longer meaningful? A. 6 MV B. 10 MV C. 12 MV D. 18 MV E. 24 MV
B. 10 MV
The reference depth for the Tissue Phantom Ratio, TPR, is: A. dmax. B. 5 cm. C. 10 cm. D. dependent on measurement choice.
D. dependent on measurement choice.
What is TPR 20/10 a measure of? Is it dependent on or independent of the electron contamination in the incident beam?
Independent of the electron contamination in the incident beam
What is PDD 10?
PDD at 10cm depth
What is d-max?
Depth of the maximum dose
Where are PDD10 and TPR20/10 measured (what part of the beam)?
On the central axis of the boom
With TPR, does the SSD change?
Yes, SSD changes to change depth
Does scatter increase or decrease with field size?
Increase
With TAR, is the SCD constant? What about the measurement point?
With TAR, the SCD (source to chamber distance) and measurement point are constant
TAR varies with what 3 things?
- Depth
- Field Size
- Energy
dose at a point divided by the dose at d-max
Depth dose
