(Tuesday, 7/31/2018) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 3
Purpose: To demonstrate the use of EPID for electron beam quality assurance(QA) and pre-treatment verification with a simple approach in absorbed dose to water reconstruction: EpiDream method.
Methods: The study was performed using EPID As1000 imager on Varian LINAC, for electron beams of 6-9-12-15-18MeV. EPID was calibrated with EpiDream method to obtain the dose to water matrix at each energy-dependent reference depth from the Grey Level image using integrated images. Comparison was performed between radial and transverse profiles measured with a 0.125cm³ ionization chamber(PTW31010) and dose profiles extracted from EpiDream matrices for a 15x15cm² field size. For gantry angle of 90-270°, EpiDream and Profiler2 profiles were compared. Rescaling of each measured profile was performed using a Kriging interpolation method(step:0.02mm) to integrate differences in detector intrinsic spatial resolution. Analysis was performed considering: flatness, symmetry, penumbra and field size values. To quantify 2D-sensitivity of EpiDream method for each energy, EPID images of a 10x10cm² field size were acquired for several combinations of delivered Mus(3-300MU) and dose rate(100-300MU/min). To evaluate pre-treatment verification using EpiDream method, images of 10 irregularly clinical block electron fields were acquired for 6-9-12-15-18MeV. Validation of 2D-sensitivity and pre-treatment verification results was based on gamma analysis of EpiDream and TPS(eMCv13.6,Varian) absolute doses maps with 2%/2mm and 3%/3mm criteria, respectively.
Results: Considering flatness, symmetry, penumbra and field size values, mean deviation of EpiDream profiles with 0.125cm³/Profiler2 profiles was respectively: 0.01pp/0.03pp, 0.34pp/0.86pp, 0.5mm/0.35mm and 0.6mm/0.8mm. For 2D-sensitivity results, the mean gamma passing rates(%GPR) for 6-9-12-15-18MeV was respectively: 96.6%(SD=1.6%), 99.9%(SD=0.1%), 100%(SD=0.16%), 99.8%(SD=0.6%), 99.8%(SD=0.1%) from the range of 15 to 300MU. For pre-treatment verification results, %GPR ranged from 97.6% to 100%.
Conclusion: QA and pre-treatment verification of electron beams in 2D absolute dose using EPID is possible with EpiDream method at any angle by maximizing measurement reproducibility and optimizing time dedicated to QA process.
Funding Support, Disclosures, and Conflict of Interest: Christine Boutry, Denis Franck and Philippe Dudouet have ownership interests in DREAM SAS which is commercializing the EpiDream algorithm. Other authors have no relevant conflicts of interest to disclose.
Keywords
Portal Imaging, Electron Therapy, Quality Assurance
Taxonomy
TH- External beam- electrons: portal dosimetry
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