Abstract
Intensity Modulated Radiation Therapy (IMRT) is a complex treatment modality that
requires pre-treatment patient-specific quality control (QC) in order to assess a
correct treatment delivery. The aim of this work is to investigate pre-treatment patient-specific
per-field QCs performed with an on-board EPID at the gantry angle of 0° and at the
treatment ones, and to asses if measurements executed at 0° are able to guarantee
a correct treatment.
Ten patients with prostate cancer were evaluated. Two “verification” plans were created
for each patient in order to calculate the dose at the EPID surface: one with all
fields positioned at 0° and one with all fields at the actual treatment angles.
EPID’s mechanical shifts due to gravity effects were always taken into account and
corrected.
0 and no-0 plans were compared using a gamma-index method (3%, 3 mm). The gamma index
was found dependent on gantry angles but the difference between 0 and no-0 samples
was small (−0.3% mean value) and the criteria of acceptability of the gamma method
was always satisfied for every field delivered at angles different from 0.
Therefore patient-specific pre-treatment QCs should be done at treatments angles,
but, if periodical quality assurance is performed on dynamic MLC for different gantry
angles, this requirement was shown not strictly mandatory and pre-treatment IMRTQC
can be reasonably executed at 0° angles too.
Keywords
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Article info
Publication history
Published online: January 27, 2012
Accepted:
January 12,
2012
Received in revised form:
January 8,
2012
Received:
February 27,
2011
Identification
Copyright
© 2012 Associazione Italiana di Fisica Medica. Published by Elsevier Inc. All rights reserved.
