Treatment Planning Flashcards
the following is describing INVERSE or FORWARD planning?
-3D trt plans
-trial and error method
-planner chooses beam energy, beam number & direction, beam size & shapes, beam modifiers, etc
-computer then calculates dose distribution
FORWARD planning
the following is describing INVERSE or FORWARD planning?
-IMRT trt plans
-planner chooses dose & tolerances to organs
-computer generates trt plan w/ beam energy, beam shapes, beam direction, etc.
INVERSE planning
describe “Plan Optimization”
computer generates a plan but the planner adjusts it, then the computer RE-adjusts once again, to achieve the best possible plan
for INVERSE trt planning, a _____ dose is set
minimum dose is set
describe what a “minimum dose” is
it is a dose that would NOT result in a known effect, like a max dose (TD 5/5; 3/3)
-it is a type of parameter
Plan Optimization happens for only Forward planning, only Inverse planning, or both?
both!
DVH stands for what?
Dose Volume Histogram
a ______ provides information on the dose distributions to different organs, including the PTV and OARS w/i the radiation field
DVH
on a DVH, when the curve intersects the horizontal axis, this typically is where ____ is at
max dose
T/F: a DVH does NOT replace an isodose line distribution
TRUE they are separate things
what does the vertical line (y) on a DVH show?
the vertical line (y) shows the percent of the organ or the volume of tissues
what does the bottom horizontal line (x) show?
the bottom horizontal line (x) shows the dose and can be expressed in Gy, cGy, or percent %
_____ are treatment planning tools used to evaluate doses to normal tissues and tumors
DVH’s
what must happen in planning, for organs to be included on the DVH?
they must be contoured
this is an example of what?
DVH (Dose Volume Histogram)
when contouring we are assigning a ______ of the scan to a specific organ
*hint - pixel or voxel
voxel
–> a volume element
… the system then determines how much dose the specific voxel is getting and adds it up for the whole organ to express on the DVH
reading a DVH example - what is the max dose of the stomach *according to this example –>
2200 cGy
higher energy beams have ___more deep/less deep___ isodose charts and why?
more deep (deeper) isodose charts because more penetrating
what graphs/charts/curves/etc. represent dose in the body; areas in body that receive dose?
isodose curves
what are the intervals isodose curves are drawn at?
parallel and perpendicular directions of the radiation beam
what factors effect isodose curves? (6)
- beam energy
- SSD
- field weighting
- beam modifiers
- field size
- beam type
a _____ field size will cause more scatter, making for ___shallow/deeper___ isodose lines
a larger FS will cause more scatter, making for deeper isodose lines
*recall we can lower the MU to compensate
isodose curves are expressed in _____ at specific depths
percents
label the following isodose curves as –>
-electrons
-photons with wedge
-photons
- photons
- photons with wedge
- electrons
_______ are used to help reduce areas of overlap in trt plans with multiple fields and hinge angles less than 180 degrees
–also used for tissue compensation in areas OF SLOPING SURFACES, like breast
wedges
**to help not get bolus and wedges confused focus on how it says sloping surfaces = wedge
a standard wedge, would be a physical wedge or dynamic?
physical
where are physical wedges/standard wedges placed? and what is their typical material?
physical wedges are slipped into the collimator and are made of lead or steel
how are dynamic wedges created?
by moving a jaw within the treatment head
-JAW!!!! not MLC
the ___ of a wedge brings isodose curve up higher to surface within patient
heel
–decreases the penetration of beam due to attenuation happening within thicker part of wedge (heel)
the _____ of a wedge allows for MORE transmission of the beam!!!
toe
-thinner part of wedge, less attenuation
many say wedge depth definition/angle is at the _____% isodose curve or a ___cm depth for higher energies
50% isodose curve
or 10 cm depth
label parts of this isodose curve diagram -
- wedge’s toe
- MORE dose getting into patient – going deeper – because more beam transmission
- LESS dose getting into patient – more shallow – because less beam transmission due to increased attenuation
- attenuation
- wedge’s heel
- patient’s surface
dose is greatest where?
at central axis!!!
_____ region is on the beam’s edge
penumbra
field size is defined where/when? - for photon
at the 50% isodose line
the following is an example of a ___________
beam profile
if there is a flattening filter on a photon beam and we look at the beam prifile… what can we expect to see on it?
horns
photons use what filter/foil? what about electrons?
photons = flattening filter
electrons = scattering foil
________ = rapid fall of due to side scatter
penumbra
where/when does penumbra occur?
between 90-20% isodose lines
…this is why beam flatness is only measured on inner 80% of beam
