Geometric Parameters and Patient Measurements/Treatment Planning Parameters Flashcards
Treatment Planning Parameters
measurements of the treatment field are defined at _______________
isocenter
(width x length)
how is a field size created?
hint - probably more in depth than you’re thinking
created by two pairs of the secondary asymmetric collimator jaws
from a base field size, fields can be further shaped via _________
MLCs/and or custom Cerrobend blocks
_____ are a document of the field parameters
DRRs
the physical radiation field size is delineated at the _____% isodose line
50%
what happens to the physical radiation field size at the 50% isodose line?
it is delineated
tumor depth is established with ____ imaging
3D imaging
tumor depth/depth of a tumor determines ________ and ______ according to Laura Nappi
-the energy of the beam
-the type of treatment
superficial tumors are most likely to be treated with __________
electrons
deeper tumors are most likely to be treated with __________
photons
“Patient Separation” can also be called what? (looking for 3 other names)
- patient thickness
- intrafield distance
- innerfield distance (IFD)
what does IFD stand for?
Innerfield Distance
what does DRR stand for?
Digitally Reconstructed Radiograph
patient separation is measured how and where?
- measured at central axis and at specific points within the treatment field
*think about in class with megan and graph paper and wire
patient separation can be measured using what type of tool?
caliper
what is a caliper?
a ruler with one sliding leg and one stationary leg
what does SSD stand for?
Source to Skin/Surface Distance
what does SAD stand for?
Source to Axis Distance
the following is describing SAD or SSD?
- 100 cm OR it is possible to have it at another specified “fixed”
- used for electron fields or to be able to obtain larger field sizes
- used for electron fields
- distance from the source of radiation to the patient’s skin surface
-typically what is taken every 5th trt day
SSD
the following is describing SAD or SSD?
- in current LINACS it is located at 100 cm, in older Cobalt-60 machines it is at 80 cm
- Isocentric technique
- distance from source of radiation to isocenter (within patient)
- should never change
SAD
T/F:
isocenter can be within or on a patient
TRUE
tumor within or superficial tumor!
define “isocentric technique”
when the isocenter is located WITHIN the PATIENT
for an isocentric technique SSD is what?
less than 100 cm
does a patient need to be moved between fields of an isocentric technique?
No
are there more or less chances of error with an isocentric trt?
less
T/F:
if using an isocentric or SAD technique, the SSD WILL change at different gantry angles
hint - think about clinic and when you check different SSDs like a true lat or AP
TRUE
there is more chance of error using an SSD or SAD trt
SAD is a more sure way, with less chance of error
what can an isocentric technique also be called? -
SAD technique
T/F:
for an SSD technique trt, a patient may need to be moved between fields
TRUE
-which causes more chance of error
the _________ collimating jaws are movable and asymmetric
secondary
secondary collimating jaws can create __________ field sizes ranging from __x__ cm to ___x___ cm at the isocenter
-rectangular
0x0 cm to 40x40 cm
jaws are made of what material?
tungsten
only ____ percent of transmission through jaws is permitted
only <0.5%
as field size increases, does collimator scatter decrease OR increase
INCREASE
T/F:
collimator scatter contributes to dose a patient receives
TRUE
collimator scatter contributes to dose, therefore, less ____ is needed
MU (monitor units)
abutting or adjacent fields meet at a determined depth within the patient because of ____________
beam divergence
to avoid hot spots or cold spots, there must be a _____ on the skin surface
gap
to avoid hot spots or cold spots, there must be a gap, where?
on the skin surface
what calculation is commonly used in CSI (craniospinal irradiation)
gap calculation
what is a common orthogonal field area of possible overlap for CSI (craniospinal irradiation)?
laterals for the cranium and PA fields for the spine
*Scenario: CSI (craniospinal irradiation)
___________ causes overlap between the cranium and spine fields, and between the multiple spine fields
beam divergence
what are other techniques to avoid overlap besides the gap calculation? (3)
- half-beam block
- beam splitters
- couch rotation (kick)
__________ is a technique used to move or change the location of the gap throughout the treatment
feathering
T/F:
feathering position is adjusted at least 2-3 times throughout the treatment, usually every 5 fractions
TRUE
_______ blurs any inhomogeneous (not the same) doses within the gap area
feathering
with Feathering, the ________ axis remains the same, but the field ______ change
the central axis remains the same
but the field lengths change
image ______ uses multiple imaging modalities to provide better visualization of the patient’s anatomy -
–> the images from the multiple sources are laid over one another to create a more informative image
image fusion
the following is an example of image fusion - what two images are fused?
MRI and CT
the following is an example of image fusion - what two images are fused?
PET and CT
what is another name for the treatment planning computer?
Virtual Simulator
in the _______ simulator, the physician identifies treatment borders and isocenter
virtual
what scans are useful for soft tissue?
MRI
-commonly used for prostate
what scans are useful for showing tumor activity?
PET
-commonly fused for lung and HN
T/F:
multiple different scans can be fused together to provide for better visualization of the patient’s anatomy
TRUE
abutting fields meet at a determined depth within the patient because of what?
beam divergence
for abutting fields, gap is calculated to avoid what? (2)
hot and cold spots
abutting fields and gap calcs are commonly used for what treatment?
CSI - Craniospinal
_______ ________ causes overlap between the cranium and spine fields and - between the multiple spine fields
beam divergence
techniques such as - half-beam block, beam spoilers, or couch kicks/rotations are used to avoid what?
overlap and hot spots
