ESTRO course Dose Modelling and Verification 2017

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

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