In vivo dosimetry Flashcards
Purpose of IVD
-detect major errors
-assess differences between planned and delivered dose
-record the dose
-Fulfil legal requirements
build up cap
-put on top of dosiemtre (made of tissue equiv. material)
-used to get a signal from detector
-isnt put in central axis
build up cap problems
loss of e- equilibrium
-underdosage
-used for a few fx bc of change of dose distribution
build down cap
cant be put directly under build up cap
semiconductors
normally insulators, not alot of mobile e-
but we can increase conductivity thru some methods
methods
-heating up= ↑energy=e move
-doped semiconductors by adding v small am of particular atoms
these particular atoms=
donor= add e- (arsenic)= n type
acceptor= add holes (boron) - p-type
what is a diode
device where ptype material and ntype material connect
ptype mat=extra holes
ntype mat=extra e-
when material combine and interact=creation of depletion zone (zone that is sensitive to radiation tf becomes detector)
characteristics of diodes:
signal stability after irradiation
reproducibilty
sensitivity
dose response
- 1 hour
-reproducible for at least 10 irr
-highly variable from diode to diode.. varies w temp
-linear up to at least 10Gy
equilibrium temp
32
diode memory effect
-starts after lifetime of use
-happens by some holes created by radiation and combine w e-
-tf less charge carriers being detected
diode memory effect leads to
↓in sensitivty whihc is more important for high energy e- than photons
diode advantage
rapid read out
diode disadvantage
*Temperature/dose rate/energy dependence
diode use
- Small field dosimetry
- Electron measurements
