Abstract
We present a study of the under-response of the new Gafchromic EBT3 films and a procedure
to accurately perform 2D and 3D proton dosimetry measurements for both pristine and
spread out Bragg peaks (SOBP) of any energy. These new films differ from the previous
EBT2 generation by a slightly different active layer composition, which we show has
not effected appreciably their response. The procedure and the beam quality correction
factor curve have been benchmarked using 29 MeV modulated proton beams. In order to
show the correction to apply when EBT3 films are used as treatment verification tools
in anthropomorphic phantoms, two simulation studies involving clinical energies are
presented: a SOBP for eye treatments and a SOBP to treat 20 cm deep and 5 cm thick
tumours. We find maximum under-responses of 37%, 30% and 7.7% for the modulated 29 MeV
beam, eye and deep tumour treatment, respectively, which were attained close to the
end of the peak tails, due to a higher proportion of very low energy protons. The
maximum deviations between corrected and uncorrected doses were for the three cases,
respectively, 20.7%, 8.3% and 2.1% of the average dose across flat region of the SOBP.
These values were obtained close to the distal edge of the SOBPs, where the proportion
of low energy protons was not as high as on the tail, but there still was a number
of protons high enough to deposit a reasonable amount of dose in the films.
Keywords
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Article info
Publication history
Published online: January 24, 2014
Accepted:
December 30,
2013
Received in revised form:
November 24,
2013
Received:
August 7,
2013
Identification
Copyright
© 2014 Associazione Italiana di Fisica Medica. Published by Elsevier Inc. All rights reserved.
