Radiation Fields Flashcards by Olivia Miller

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

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a single field, can also be called a single ____

port

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single fields are used to treat what type of treatments?

superficial electron fields or palliative trts

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why aren’t single fields super common?

because the dose distribution is not ideal for MV beams

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the following are examples of which radiation field?

-AP IM chain
-PA spine
-supraclavicular nodes

single field

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the following is an example of what radiation field?
*hint - notice there is no high isodose line on other side of patient

single field

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T/F: you can use “Field” and “Port” interchangeably

TRUE

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Parallel Opposed Fields (POPs) have ___ treatment fields/ports aimed at/in opposing directions

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POP stands for -

Parallel Opposed Ports

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POPs have a hinge angle of _____ !!!

180 degrees

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POPs have a ______ dose distribution !!!

homogenous

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POPs are used for more ____curative/palliative____ treatments?

curative

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for POPs 2 fields are aimed along the same ____ from opposite sides

same axis

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AP/PA and RT lat/LT lat are examples of what radiation field?

Parallel Opposed Fields//Ports

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POPs lead to higher ____ doses, therefore it is even more common to use more than two fields to reduce these reactions

skin

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_____ are the simplest form of multiple fields, and are very reproducible

POPs

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_____ have a homogenous dose to tumor

POPs (Parallel Opposed Ports/Fields)

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the following is an example of what radiation field?

POPs (Parallel Opposed Ports/Fields)

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For which radiation field, is there less sparing of tissues around tumor - when it is compared to the other techniques

POPs

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good note - in general, multiple fields (so anything over a single field) are used more for ___curative/palliative___ treatments

curative

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___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

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a “hot spot” would indicate overdose, or underdose?

overdose

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a “cold spot” would indicate overdose, or underdose?

underdose

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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

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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

1. -where the past point is 2. -where the dmax is with use of past pointing 3. - 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)