Radiation Fields Flashcards
T/F: radiation fields can differ depending on location of tumor and depth of tumor
TRUE
-every plan and patient can be unique however there are some standards
a single field, can also be called a single ____
port
single fields are used to treat what type of treatments?
superficial electron fields or palliative trts
why aren’t single fields super common?
because the dose distribution is not ideal for MV beams
the following are examples of which radiation field?
-AP IM chain
-PA spine
-supraclavicular nodes
single field
the following is an example of what radiation field?
*hint - notice there is no high isodose line on other side of patient
single field
T/F: you can use “Field” and “Port” interchangeably
TRUE
Parallel Opposed Fields (POPs) have ___ treatment fields/ports aimed at/in opposing directions
2
POP stands for -
Parallel Opposed Ports
POPs have a hinge angle of _____ !!!
180 degrees
POPs have a ______ dose distribution !!!
homogenous
POPs are used for more ____curative/palliative____ treatments?
curative
for POPs 2 fields are aimed along the same ____ from opposite sides
same axis
AP/PA and RT lat/LT lat are examples of what radiation field?
Parallel Opposed Fields//Ports
POPs lead to higher ____ doses, therefore it is even more common to use more than two fields to reduce these reactions
skin
_____ are the simplest form of multiple fields, and are very reproducible
POPs
_____ have a homogenous dose to tumor
POPs (Parallel Opposed Ports/Fields)
the following is an example of what radiation field?
POPs (Parallel Opposed Ports/Fields)
For which radiation field, is there less sparing of tissues around tumor - when it is compared to the other techniques
POPs
good note - in general, multiple fields (so anything over a single field) are used more for ___curative/palliative___ treatments
curative
___less/more___ fields allow for higher doses to the tumor and lower doses to surrounding OARs
more!!!! with more fields you can conform to tumor better and find more angles to avoid OARs
a “hot spot” would indicate overdose, or underdose?
overdose
a “cold spot” would indicate overdose, or underdose?
underdose
Concept Check! - For parallel opposed fields, the fields must be parallel… so if they are NOT fully opposing… what would you check/fix?
check to see if between the 2 parallel opposed fields the collimator was flipped OR if the jaws were flipped/reversed
–one or the other, not both collimator AND jaws
if both the collimator and jaws were flipped for your POPs, is this good or bad? and Why
bad - only one can flip/be reversed… because if BOTH the collimator and jaw were flipped between fields, it will be like nothing changed on the opposite field
if using blocks for POPs what must you do between fields?
FLIP THEM
–tbt to sim lab!
the following is a POP field, can we treat if it looks like this?
NO - the POPs are not fully opposed
for POPs, the gantry is the exact _____ between the 2 fields, and field size is a ____ image
gantry is exact opposite (ie. parallel) and field size is a mirror image
why does the POP fields look like this? is it wrong or right?
because neither the collimator or field size were adjusted
in the following POP example - is the collimator or jaws adjusted?
collimator
in the following POP example - is the collimator or jaws adjusted?
jaws
____ are used when dose distribution is uneven
WEDGES
wedges are always positioned ____ to ____
heel to heel
if a wedge is positioned heel to toe, what happens?
they just cancel each other out
when an odd number of fields are used (like a 3-fld technique), there is ___even/uneven____ dose distribution
uneven — a wedge is then applied
3-field techniques are commonly used for what type of tumors?
tumors within the abdomen that are closer to the surface; anteriorly positioned tumors
looking at the example of the 3-fld technique below, where would the tumor be positioned?
anteriorly
looking at the example of the 3-fld technique below, where would the tumor be positioned?
more posterior
in the following diagram, the heel of the wedge is placed more anterior or posterior? - and WHY
more anterior - it is good that heel is placed anteriorly because there is an AP field part of the 3 flds, so there would be more dose there than anywhere else. Having the heels anteriorly, reduce hot spot/overdose and even out dose
what radiation/treatment field(s) is/are used for tumors deep within the abdomen or pelvis?
4 field technique
4 field technique is also known as what?
4 field box
each field of a 4 field box/technique are ___ degrees apart
90 degrees
what radiation field is considered a combination of two parallel opposed fields?
a 4-field box/technique
the following diagram is of what radiation field?
4 field box/technique
what radiation field is used for small, superficial tumors that are up to 7 cm within skin surface
wedge pair
if we treated the parotid gland, what radiation field(s) would we be likely to use?
a wedge pair
a wedge pair radiation field has a hinge angle of ______
LESS THAN 180 degrees
T/F: for a wedge pair technique where the beams overlap there is still higher dose
true!! for a wedge pair technique, where the beams overlap is where we want max dose to be - the wedges are just employed to help reduce hot spots
for a wedge pair technique, there is rapid ______ after the area of overlap
dose fall off
why is a wedge pair technique optimal for superficial tumors?
after the area of overlap, there is rapid dose fall off - thus reducing dose distally for OARs
a ____ angle is the angle between 2 fields !!!!!
HINGE
for a wedge pair radiation field, a hot spot of ___% is acceptable, but nothing higher
+10%
where is dose highest at for a wedge pair radiation field?
dose is highest at the superficial/proximal region of overlap
the following diagram is of what radiation field(s)?
wedge pair technique
for which radiation field is the gantry stationary while the beam is ON?
a fixed field
for a fixed field(s), the gantry moves when?
in between trt fields… does not move while the beam is ON
another name for fixed fields is _________
step n’ shoot
to help identify fixed fields, you can look for what effect?
the starfish effect!
the starfish effect on fixed fields, represents what?
each individual exit dose
the choppy green on this diagram of a Fixed Field is representing what effect?
the starfish effect
which radiation field has the gantry moving, while the beam is on?
rotational fields/VMAT arcs
which radiation field(s) are BEST for small deep-seated tumors?
rotational arcs/fields ; vmat
the following is fixed fields or rotational fields?
rotational - not as choppy like starfish effect… rotational has smoother lines (also there are arrows rotating around patient contour)
of what radiation field(s) does it’s dmax get displaced anteriorly?
partial arcs
for partial arcs the gantry moves LESS THAN ____
360 degrees !!!! makes sense - not a full arc, a partial! so not going full 360 degrees
for a full arc the gantry rotates ____
a full 360 degrees
a full arc dmax is located at the ___
center/isocenter
a partial arc dmax is located where?
more anterior … to help correct for that we use past pointing
past pointing is used for partial arcs why?
past pointing (PP) has the trt planned past the tumor THAT WAY dmax lands ON the tumor
to help trick the machine into placing dmax at isocenter for a partial arc, we use ______
PP (past pointing)
past pointing corrects ____ arc dmax misplacement
partial arc dmax displacement
for a partial arc, we plan to trt at a past point, that way what happens?
that way dmax ends up where we want/desired depth
label in the following partial arc diagram -
- where dmax is w/o past pointing
-where the past point is
-and where the dmax is with use of past pointing
- -where the past point is
- -where the dmax is with use of past pointing
- where dmax is w/o past pointing (notice how it winds up more anterior in body)
what radiation field is being used in the diagram?
PARTIAL ARC – we know this due to isodose lines only covering one side of head AND looking at partial arrow ; don’t get it confused with wedge pair… there are not wedges here!!!
field weighting can also be called what?
beam weighting
how can you calculate dose per field? what about MU per field?
Dose per field = Total Dose x (weight of field/sum of all field weights)
MU per field = Total MU x (weight of field/sum of all field weights)
T/F: different fields//beams can deliver unequal amounts of dose
true
calculate the dose delivered to the PA field
200 cGy
**dose per field = TOTAL DOSE x (weight of field / sum of all field weights)
