Accessory Devices Flashcards
briefly define beam restrictors
devices that confine the radiation beam
name some beam restrictors
cones
collimators
diaphragms
beam restrictors contribute to penumbra, what are the 2 types
geometric penumbra - due to source size and SSD
transmission/collimator penumbra - due to non-diverging collimators
briefly define beam modifier and name some types
pieces of equipment used to change the shape of the treatment field or distribution of radiation
shielding blocks, MLC, bolus, compensators, wedges
what is a wedge
typically made of lead
a wedge shaped piece of dense material
attenuates beam more on thick end
results in tilted isodose curve
what is the wedge angle (not calculation)
angle defining the extent of the isodose tilt
how is the wedge angle defined
intersection of the CAX and the 50% isodose line
why dose the tilt of isodose lines due to wedges decrease at a depth
due to attenuation within the tissues
name some standard wedge angles
15, 30, 45, 60
why does a wedge transmission factor need to be added
because there is a degree of scatter coming from the wedge
what is a dynamic/virtual wedge
dynamic - referring to the movement of the wedge is occurring during tx
virtual - wedged distribution is delivered without the use of a physical wedge
the side of the treatment field where the jaw starts its movement represents the _____ end of the physical wedge
thin
how is the wedge angle controlled when using dynamic wedges
the speed of jaw movement and the dose rate control
increased angle - slower jaw movement - or higher dose rate
what are some advantages for virtual wedges
saves space
dont need to move it - this could refer to during treatment for diff fields or removal after treatment
what are some disadvantages
cannot visualize
if programmed wrong it will carry through all tx
