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D(z,c)=D
R
*MU*O
R
(c)*TPR(z,c)*
(f
r
/f)
2
*V
corr
(f
r
/f)
2
is the distance correction factor, based on the
inverse square law relationship
f
is the point-to-source distance under non-isocentric
conditions
f
r
is the point-to-source distance under isocentric
conditions
V
corr
is a correction factor for altered irradiated volume
and thus scatter
·
Non-isocentric beams