Dose Course 2018_Flipping book

TRS-483: basic concepts of small fields

Definition of field size

• 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.

[ ] = 8.369 ×

10 − 4.382

LCPE

20,10

: field with dimensions close to the 10 cm × 10 cm

Machine specific reference (msr) field, f msr :

•

reference field on high energy photon beam generators that cannot establish the latter

f

beam quality of machine specific reference field

Q

machine specific reference field

msr

msr