SSD and SAD Flashcards
SAD stands for what?
Source to Axis Distance
SSD stands for what?
Source to Skin Distance
____ is also known as TAD, Target to Axis Distance
SAD
SSD or SAD measures distance from source of radiation to isocenter
SAD
SSD or SAD measures distance form source to skin surface
SSD
____ is also known as TSD, Target to Skin Distance
SSD
in current LINACs, SAD = ____ cm and in old Co-60 machines SAD was ___ cm
current LINACs have 100 cm SAD – old Co-60 machines had 80 cm SAD
describe isocentric technique -
when the isocenter is located within the target/tumor
which set-up is more accurate and why? : SAD or SSD
SAD because patient does not need to be moved in-between treatment fields increasing the accuracy
SAD reads __less/more___ at patient’s skin surface. and Why
SAD reads less at patient’s skin surface, because isocenter is somewhere within patient
T/F: SSD trts have a fixed SSD for EACH trt field?
TRUE
why are SAD trt more accurate than SSD trts?
because for SSD trts, the patient is moved between fields (if there are multiple fields) making more chance for error
label the green and pink of the picture - either SAD or SSD
green = SSD
pink = SAD
________ = patient thickness
patient separation
what can “patient separation” also be called?
intrafield distance and or innerfield distance (IFD)
what makes up a patient’s thickness/separation?
distance from the entry point of the beam on the skin surface to the exit point on the opposite end of the patient’s body
patient separation is measured along the ______ of the beam
central axis
patient separation can be measured using a physical tool called a __________ or digitally. Explain how digitally?
Caliper for physical; digitally is done on an axial slice of a 3D image such as a CT
when talking patient separation, the term “midplane” refers to what?
the exact middle of the measurement of the patient’s separation
patient separation example question -
answer = 12.5 cm
patient separation example question -
answer = 9 x 10.8 cm
patient separation example question -
answer = 12.75 cm
what is equation to find patient separation?
set up ratio –> * FS = Field Size
(FS 1 / SSD 1) = (FS 2 / SSD 2)
what is good check when completing patient separation calcs? - if you are trying to find SSD FS and you have SAD FS, the correct answer for SSD FS will be __larger/smaller___ than SAD FS … and vice versa
*FS = Field Size
smaller
in the diagram below - what is the orange? what is the yellow?
orange = midplane
yellow = patient’s separation/thickness
