SSD and SAD

Question 1

SAD stands for what?

Answer 1

Source to Axis Distance

Question 2

SSD stands for what?

Answer 2

Source to Skin Distance

Question 3

____ is also known as TAD, Target to Axis Distance

Answer 3

SAD

Question 4

SSD or SAD measures distance from source of radiation to isocenter

Answer 4

SAD

Question 5

SSD or SAD measures distance form source to skin surface

Answer 5

SSD

Question 6

____ is also known as TSD, Target to Skin Distance

Answer 6

SSD

Question 7

in current LINACs, SAD = ____ cm and in old Co-60 machines SAD was ___ cm

Answer 7

current LINACs have 100 cm SAD – old Co-60 machines had 80 cm SAD

Question 8

describe isocentric technique -

Answer 8

when the isocenter is located within the target/tumor

Question 9

which set-up is more accurate and why? : SAD or SSD

Answer 9

SAD because patient does not need to be moved in-between treatment fields increasing the accuracy

Question 10

SAD reads __less/more___ at patient’s skin surface. and Why

Answer 10

SAD reads less at patient’s skin surface, because isocenter is somewhere within patient

Question 11

T/F: SSD trts have a fixed SSD for EACH trt field?

Answer 11

TRUE

Question 12

why are SAD trt more accurate than SSD trts?

Answer 12

because for SSD trts, the patient is moved between fields (if there are multiple fields) making more chance for error

Question 13

label the green and pink of the picture - either SAD or SSD

Answer 13

green = SSD
pink = SAD

Question 14

________ = patient thickness

Answer 14

patient separation

Question 15

what can “patient separation” also be called?

Answer 15

intrafield distance and or innerfield distance (IFD)

Question 16

what makes up a patient’s thickness/separation?

Answer 16

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

Question 17

patient separation is measured along the ______ of the beam

Answer 17

central axis

Question 18

patient separation can be measured using a physical tool called a __________ or digitally. Explain how digitally?

Answer 18

Caliper for physical; digitally is done on an axial slice of a 3D image such as a CT

Question 19

when talking patient separation, the term “midplane” refers to what?

Answer 19

the exact middle of the measurement of the patient’s separation

Question 20

patient separation example question -

Answer 20

answer = 12.5 cm

Question 21

patient separation example question -

Answer 21

answer = 9 x 10.8 cm

Question 22

patient separation example question -

Answer 22

answer = 12.75 cm

Question 23

what is equation to find patient separation?

Answer 23

set up ratio –> * FS = Field Size
(FS 1 / SSD 1) = (FS 2 / SSD 2)

Question 24

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

Answer 24

smaller

Question 25

in the diagram below - what is the orange? what is the yellow?

Answer 25

orange = midplane
yellow = patient’s separation/thickness