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Field size
≡ irradiation field size (IEC TR 60788, 2004): the pair of dimensions on radius that defines
the area of the field at the measurement distance. Each dimension is defined by the FWHM of the
lateral beam profile
•
Equivalent square small field size
(for the purpose of selecting field output correction factors)
•
Lateral charged particle equilibrium range
, r
LCPE
: the minimum radius of a circular field for which
the absorbed dose to water at the centre of the field is related by a constant factor to the water kerma
in water. Used for establishing the
relationship between field size and minimum detector size
for
which LCPE conditions exist.
•
Machine specific reference (msr) field,
f
msr
:
: field with dimensions close to the 10 cm
×
10 cm
reference field on high energy photon beam generators that cannot establish the latter
TRS-483: basic concepts of small fields
Definition of field size
LCPE
[ ] = 8.369 ×
20,10
10 − 4.382
msr
Q
beam quality of machine
specific reference field
msr
f
machine specific
reference field