TAR + Flashcards
Tissue Air ratio
T=Dtissue/Dair
dtissue=
dair=
- absorbed dose at some location of medium
- absorbed dose to a small mass of tissue suspended in air at same location
TAR is the ratio of
absorbed dose at a given depth in phantom to AD at same point in free space
what is build up cap
small piece of phantom just big enough to overcome skin sparing affect
TAR depends on
feild size. – fs ↑ TAR↑
energy— e ↑ TAR↑
depth— depth ↑ TAR↓
The tissue/phantom ratio (TPR) is
ratio of dose at given depth in phantom TO dose at a reference depth dose
dose in tissue /dose in phantom @ reference dose depth
where is TPR measured
in phantom therefore no build cap needed
TMR (Tissue max ratio)
TPR but ref dose is @ d max
TPR and TMR both depend on
independent on
- feild size… ↑fe ↑TPR/TMR
- energy …↑e ↑ ‘’
- depth… ↑d ↓’’
distance
Scatter Air Ratio (SAR)
ratio of scattered dose at a given medium TO dose in air at that same point
SAR depends on
independent on
feild size
energy
depth
distance
how does TMR differs from TAR
tissue equivalent phantom produces backscatter
TMR =
TAR/PSF
