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51

Possible errors and expected consequences

Oncentra examples

• Build-up blurring from finite sized ion chambers

=>

bad electron contamination fit

• Penumbra blurring due to ion chamber long axis along beam edge

=>

bad effective source size fit =>bad small field D/MU

• Partly blocked ion chambers for small fields OFair

=>

bad effective source size fit =>bad small field D/MU

• Depth offset

=>

bad effective spectrum fit, wrong depth doses (but not as

measured!)

• Noisy data

=>

error analysis difficult

• Too thin or too low density of build-up cap for

S

c

meas.

=>

bad values of flat.filt.scat. parameters=>overestimated output

variation