Case#$4$: Patient is treated with $100$ SAD technique with AP & PA fields. The patient's separation is $16cm.$

The physician is prescribing to mid$-$plane and the isocenter is placed there. Field Size is $1515cm.($Draw out

the set$-$up and answer questions$)$

What is the SSD of this set$-$up$?$

Where is the field size defined?