Dose Course 2018_Flipping book

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)

2

S

( a b S a b a b  = + 

Perimeter Area

S =

)

4 2

or

S

=

2

" 4" PA

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).