Erschienen:
Cambridge University Press (CUP), 2018
Erschienen in:Journal of Radiotherapy in Practice
Sprache:
Englisch
DOI:
10.1017/s1460396917000486
ISSN:
1460-3969;
1467-1131
Entstehung:
Anmerkungen:
Beschreibung:
<jats:title>Abstract</jats:title><jats:sec id="S1460396917000486_abs1" sec-type="general"><jats:title>Background</jats:title><jats:p>Electronic portal imaging device (EPID) offers high-resolution digital image that can be compared with a predicted portal dose image. A very common method to quantitatively compare a measured and calculated dose distribution that is routinely used for quality assurance (QA) of volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy treatment plans is the evaluation of the gamma index. The purpose of this work was to evaluate the gamma passing rate (%GP), maximum gamma (<jats:italic>γ</jats:italic><jats:sub>max</jats:sub>), average gamma (<jats:italic>γ</jats:italic><jats:sub>ave</jats:sub>), maximum dose difference (DD<jats:sub>max</jats:sub>) and the average dose difference (DD<jats:sub>ave</jats:sub>) for various regions of interest using Varian’s implementation of three absolute dose gamma calculation techniques of improved, local, and combined improved and local.</jats:p></jats:sec><jats:sec id="S1460396917000486_abs2" sec-type="general"><jats:title>Methods and materials</jats:title><jats:p>We analyzed 232 portal dose images from 100 prostate cancer patients’ VMAT plans obtained using the Varian EPID on TrueBeam Linacs.</jats:p></jats:sec><jats:sec id="S1460396917000486_abs3" sec-type="results"><jats:title>Results</jats:title><jats:p>Our data show that the %GP, <jats:italic>γ</jats:italic><jats:sub>max</jats:sub> and <jats:italic>γ</jats:italic><jats:sub>ave</jats:sub> depend on the gamma calculation method and the acceptance criteria. Higher %GP values were obtained compared with both our current institutional action level and the American Association of Physicists in Medicine Task Group 119 recommendations.</jats:p></jats:sec><jats:sec id="S1460396917000486_abs4" sec-type="conclusions"><jats:title>Conclusions</jats:title><jats:p>The results of this study can be used to establish stricter action levels for pre-treatment QA of prostate VMAT plans. A stricter 3%/3 mm improved gamma criterion with a passing rate of 97% or the 2%/2 mm improved gamma criterion with a passing rate of 95% can be achieved without additional measurements or configurations.</jats:p></jats:sec>