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Phantom scatter: equivalent square of a rectangular field
Area over perimeter method
(Sterling et al 1964 BJR 37, 544; Patomaki 1968, BJR 41,381 etc)
" 4"
PA
or
Perimeter
Area
S
=
(
)
2
4 2
2
S
a b
S a b
a b
S
a b
=
+
=
+
Method not based on sound physical principles, BUT used for years, with surprisingy
accurate results (<1%) for rectangular fields of length <20cm and length/width<4
(Day
and Aird 1996 BJR25, 138,McDermott, MedPhys 25(11), 2215, 1998).