26. Evaluation of the EpiDream method for quality assurance (QA) of electron beams using a Varian electronic portal imaging device (EPID)

• Published in: Physica medica 2016-12, Vol.32, p.353-353
• Main Authors: Sors, A, Dudouet, P, Franck, D, Boutry, C
• Format: Article
• Language: English
• Subjects: Radiology
• ISSN: 1120-1797; 1724-191X
• DOI: 10.1016/j.ejmp.2016.11.078

Introduction The aim of the study is to evaluate the use of EPID for electron beams QA defined by the 07/27/2007 French decision with a new approach in absorbed dose to water reconstruction: the EpiDream method. Methods The study was performed on two Varian LINACs, equipped with EPID (either with the AS500 or AS1000) for electron beams of 6, 9, 12, 15 and 18 MeV. Each EPID was calibrated with EpiDream application in order to obtain from the Grey Level (GL) image a dose matrix computed in water at the reference depth(zref) of the energy studied. For each energy, GL integrated images were corrected of dark field and acquired using AM Maintenance system(Varian) at the detector source distance (DSD) = 100 cm and DSD = (100 + zref) cm for different parameters : field sizes(6 × 6–20 × 20 cm2 , delivered MU (3-300 MU), dose rate(100–300 MU/min). For each irradiation condition, a gamma index evaluation was performed between dose matrix computed by Eclipse TPS algorithm (eMC v13.6, Varian) and dose matrix computed by EpiDream method (DM EpiDream). For a 15 × 15 cm2 field size, a comparison was performed between radial and transverse dose profiles measured with a 0.125 cm3 ionization chamber(PTW31010) in water at zref for SSD = 100 cm and dose profiles obtained from DM EpiDream, considering: homogeneity and symmetry parameters, penumbra and correlation coefficient. Results Data analysis is in progress. However, first results are encouraging: At 9 MeV and for a DSD = 100 + zref, the mean gamma index value for 6 × 6, 10 × 10, and 15 × 15 cm2 field sizes is respectively: 99.9% ( σ = 0.1%), 99.8% ( σ = 0.32%), 96.3% ( σ = 2.2%). Conclusions The EpidDream method would permit to perform electrons beams QA using EPID for all gantry angles by maximizing measurement reproducibility.