Treatment Accessories Flashcards
T/F: treatment accessories can further shape and effect the beam and dose distribution
true
compensators and compensating filters are designed to create ________ dose and distribution within patient
homogenous
where are compensators and compensating filters placed?
in between radiation source and patient
compensators and compensator filters must be placed ____ cm from patient during photon therapy
20 cm
where are compensators placed for electron therapy?
can be placed directly on patient
compensating filters have mostly been replaced by what?
IMRT
what is used to reduce scatter to skin surface and maintain skin sparing?
compensators and compensating filters
what are compensators and compensating filters made of?
high density materials such as Cerrobend or poly-lead
T/F: compensators or compensating filters can be custom made
true
what are compensators/compensating filters used/made for?
made to absorb dose in areas where there is missing tissue or have irregular surfaces or are curved
of BLT w/ C what are the percentages?
B = ___%
50%
of BLT w/ C what are the percentages?
L = ____%
26.7%
of BLT w/ C what are the percentages?
T = _____%
13.3%
of BLT w/ C what are the percentages?
C = _____ %
10%
Blocks are positioned on a tray meaning a ____ factor would be needed when calculating MU
tray
the following is describing Hand blocks, Cast blocks, Positive blocks, or Negative Block –>
*individualized for each patient
*cut to match beam divergence, reducing penumbra
cast block
the following is describing Hand blocks, Cast blocks, Positive blocks, or Negative Block –>
*blocks the center field and leaves periphery open
Positive block
*fist bump = the block in middle = POSITIVE
the following is describing Hand blocks, Cast blocks, Positive blocks, or Negative Block –>
*blocks the periphery and leaves the middle/center open
Negative block
the following is describing Hand blocks, Cast blocks, Positive blocks, or Negative Block –>
*pre-made and not custom
*non divergent (sides do not match angle of the beam, creating penumbra)
*high density materials
Hand blocks
what is the common thickness of Lead blocks?
6 cm
blocks are typically made of what materials?
Cerrobend or lipo-witz metal
what makes up a Cerrobend block?
Bismuth, Lead, Tin, Cadmium
what degree (C) melts Cerrobend?
74 degrees C
transmission of a radiation beam through a block is ___%
< 5 %
what is the block transmission factor? and what does it mean?
< 5%, meaning block needs to be around 4-5 HVLs thick
how do you find Cerrobend equivalent of a lead block?
multiple the lead thickness by 1.21 !!!
____ cones and cutouts are used to confine and collimate beam close to patient’s skin surface
electron
T/F: electron cones come in multiple sizes
true
T/F: e- cutouts can be customized
true
e- cutouts reduce beam transmission by how much? __%
< 5%
electron cutouts reduce beam dose rate so we must use a ____ factor when calculating MU for e- plans
cutout
what is formula for –> thickness of lead needed to stop electrons?
(1/2 of the energy in MeV) + 1
*answer should be in mm, cause e- don’t need thicker blocks like photons do
what treatment accessory shields critical structures behind treated areas
internal shields
internal shields are mainly seen during photon or e- therapies?
electron
a Z # is the same as ______ #
atomic
an internal shield is a lead covered material with a ___high/low___ atomic # (Z)
low
aluminum, wax, and plastic are example of what treatment accessories… -cutouts, -bolus, -wedges, or -internal shields
-internal shields
what areas usually call for internal shields? and what do the shields protect?
eyelids - protects optic lens, lacrimal glands; nostrils - protects nasal membranes; earlobes; lips - protects gingiva, tongue
if only lead were used for internal shields and we would not cover it low atomic # material… what would happen?
if only lead were used, uncovered, there would be too much backscatter, adding to the dose
bolus is placed ___directly/indirectly___ on skin surface
directly
_____ eliminates the skin-sparing effect in photon therapy
bolus
bolus compensates for what?
irregular surface contours
_____ eliminates air gaps in treatment field
bolus
what is bolus made of?
tissue equivalent material
T/F: bolus can be multiple thicknesses
true
wax, polystyrene, Lucite, and superflab are all possible materials of ________
bolus
bolus __lowers/raises___ dmax so dose is ___more/less___ superficial
bolus raises dmax so dose is more superficial
T/F: bolus is part of prescription and much be prescribed by rad onc in order to be used on patient
true
a beam spoiler is used mainly for what treatment?
TBI
a beam spoiler reduces skin ______ and increases surface dose
sparing
*like a giant bolus
a beam spoiler is made of __-__ cm of ____
1-2 cm of acrylic
a beam spoiler brings surface dose to __% of prescribed dose, which is what we need/want for TBI treatments
90%
where are beam spoilers placed in relation to patient
as close to patient as possible
wedges __increase/decrease__ beam’s intensity across the beam
decrease
______ tilt isodose curves
wedges
physical wedges are made of __low/high___ density material
high
______ wedges are placed in treatment head
physical wedges
universal/dynamic wedges use ____ to mimic same effect as physical wedges
jaws
on Varian machines, what jaw is used by dynamic wedges to mimic a wedge?
the Y jaw
___ of wedge absorbs beam, and the ____ transmits it
heel absorbs and the toe transmits it
_____higher/lower____ wedge angle, ie. heel is… steeper the isodose distribution will be
higher
the ___ of wedge brings the isodose curve up closer to the skin surface!
heel
-makes sense since beam there is attenuated more and there is less penetration, like there is closer you get to toe
example question for wedge heel positioning -
“if heel of wedge is positioned anteriorly on a RT lat, what is position on LT lat?”
LT lat would also have an anteriorly positioned heel
for HIGH or LOW energy beams, the wedge angle is found at the 50% isodose curve or 80%
low energy
for HIGH or LOW energy beams, the wedge angle is found at 10 cm depth
high energy
wedges can also absorb some of the primary beam, which would require a __lower/higher__ MU to compensate for loss of dose
higher
MLC stands for what?
multileaf collimators
how many MLC leaves are there typically
52-160 leaves
what are MLCs made of?
Tungsten
T/F: each MLC leaf has the ability to move independently to create a wide variety of treatment shapes
true
MLCs are controlled by what?
computer
____ reduce need for cast blocks and compensators
MLCs
what is the permissible percent through MLCs?
< 2%
IMRT plans use which MLC technique more commonly - step n shoot (MLCs do not move while beam is on) OR dynamic (MLCs move while beam is on)
dynamic
describe Step n Shoot and Dynamic MLCs -
Step n Shoot MLCs do not move while beam is on; once beam is off they move/re-shape; commonly used for 3D plans
Dynamic MLC move while beam is on; commonly used for IMRT
3D plans use Dynamic MLC or, Step n Shoot MLCs?
Step n Shoot
YES or NO - the following wedges in the picture are positioned correctly
YES
which of the two blocks is a POSTIVE BLOCK and which is a NEGATIVE BLOCK?
A = POSITIVE
B = NEGATIVE
