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Relationships between quantities
TPR from RDD measured isocentrically
cm
SAD
100
=
cm z
ref
10
=
z
cm SSD
90
=
cm SSD
90
≠
cm z
ref
10
=
SAD SDD
≠
A
B
C
To relate D to D must account for:
C A
•change in fluence according to inverse square law
•correction in phantom scatter due to the differences in field size at position A and C
(
)
(
)
(
)
p
SAD
iso
p
ref
p
SAD
iso
p
ref
A
C
A S
z cm
z cm
A S
z cm
z cm
D D
+
+
×
+
+
× =
90
90
90
90
2