Abutting Fields Flashcards
abutting fields can also be called what?
adjacent fields
abutting fields can be used for different treatments, however which one is a common treatment?
CSI (craniospinal)
describe abutting/adjacent fields -
abutting/adjacent fields are two fields next to one another that meet at a determined depth within the patient because of beam divergence
_______ reduce hot and or cold spots for adjacent/abutting fields
skin gaps
the following is depicting a CSI trt, which uses what field technique?
abutting fields
to match spine field… what is employed for the whole brain field of a CSI trt
collimation
what does CSI stand for?
Craniospinal Irradiation
in general, where photon fields are measured are at the 50% isodose line, where abutting fields connect adds up to ___%
100%
what equation does skin gaps use?
gap calc
_____ BLURS SKIN GAP and further reduces any hot or cold spots
feathering
for gap calc - when looking at which field edge to use, you want to use ___larger/smaller___ field length ?
for gap calc use the larger field length!!!; larger # will be length
what is the gap calc?
label this skin gap diagram -
- SSD1
- L1
- gap
- depth
- L2
- SSD2
- patient’s surface
in a CSI skin gap problem - what should remain the same, Length or Width? Or does both Length and Width change?
Width should remain the same, length changes
calculate the skin gap -
answer = 1.7 cm gap on skin surface
fill in the blanks -
SKIN –> DIVERGE
Concept check! EXPLAIN why/how on a CSI spine fields, on the skin there will be a gap but in the body there is not one
gap on skin but in reality the beams diverge w/i body for full coverage
typically CSI’s are treated ____supine/prone____
prone
for a CSI what fields are used to treat the brain (whole brain) and what field treat the spine?
RT and LT lats for whole brain (POPs)
single PA fld for spine
the spine and whole brain fields of a CSI are ______ junctions
orthogonal junctions
to determine a CSI COLLIMATOR angle use the ____ field length & SSD
spine!
to determine a CSI COUCH kick angle use the ____ field length & SSD
brain!
solve for the CSI collimator rotation angle -
= 6.3 degrees
**hint - use spine length because spine is long and collimator is a longer word !!!! and SSD because it has a lot of S’s
solve for the CSI couch kick rotation angle -
= 5.14 degrees
**hint - use brain because couch is shorter word than collimator and brain = SAD because SAD in brain!!!
what is equation for CSI collimator rotation?
what is equation for CSI couch rotation?
typically, for CSI in which direction do we rotate the couch?
towards the gantry
the following depicts what kind of treatment?
CSI (craniospinal)
half beam block is another method for setting up _____ fields
abutting
-seen a lot with breasts (personally)
half beam block is ____isocentric technique
monoisocentric technique
monoisocentric means there is how many isocenters?
1
for a half beam block the ___ closes to ___ and there would be no beam divergence
jaw closes to zero
a half beam block has NO beam _________
divergence
3 or 4-fld breasts typically use what technique?
half beam blocks
if using a half beam block, what is not needed/used?
no couch kicks or collimation
the following is an example of what?
a half beam block
