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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