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a. The concept of equivalent square for quantities describing
phantom scatter
Equivalent field
is defined as 'the standard’ (i.e. circular or square)
field that has the same central axis depth dose characteristics as the
given non-standard field
(Day and Aird 1996, BJR25, 138).
The equivalency between standard and non-standard fields is determined by the
requirement that the contribution to the dose along CAX from scattered photons
for the two fields be equal.
Namely, that the quantity describing phantom scatter
(e.g
scatter factor
) in the standard and non-standard field at the point of
calculation is equal.