SSD and SAD

Question 1

what does SSD stand for

Answer 1

Source Skin Distance

Question 2

in SSD the mechanical isocentre is set..

this means…

Answer 2

to skin surface

easy to measure distance (from treatment head to skin surface)

Question 3

SSD couch and central axis of beam

Answer 3

must be re-positioned for each field

passes thru isocentre

Question 4

what does SAD stand for

Answer 4

source axis distance

Question 5

in SAD , The mechanical isocentre is set

Answer 5

to a point in patient … treatment isocentre

Question 6

SAD couch and moving the gantry

Answer 6

shouldnt be repositioned for each field

keeps the treatment isocentre at at mechincal isoc.
therefore at a fixed dist from treatment head