Program Information
Development of Dose-To-Water Conversion Models for Pre-Treatment Verification with the New AS1200 Imager
N Miri*1, C Baltes2, P Keller2, P Greer3, (1)University of Newcastle, Newcastle, NSW (2)Varian Medical Systems Imaging, Baden-dattwil (3)Newcastle Mater Hospital, Newcastle, NSW
Presentations
SU-E-T-265 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:To develop and evaluate models for dose verification of flattened (FF) and flattening filter free (FFF) beams for the new Varian aS1200 backscatter-shielded electronic portal imaging device (EPID).
Methods:The model converts EPID images to incident energy fluence using deconvolution of EPID scatter kernels and fluence to dose in water using convolution with dose-to-water kernels. Model parameters were optimized using non-transmission EPID images of varying jaw defined field sizes for energies of 6 and 10 MV FF and FFF beams. Energy fluence was obtained from the Acuros planning system and reference dose profiles and output factors were measured at depths of 5, 10, 15 and 20 cm in a water phantom. Images for 34 IMRT fields acquired at 6 and 10 MV FF energy were converted to dose at 10 cm depth in water and compared to treatment planning system dose plane calculations using gamma criteria.
Results:Gamma evaluations for the IMRT fields had mean (1 standard deviation) pass rates of 99.4% (0.8%) and mean gamma scores of 0.32 (0.06) with 2%, 2 mm criteria and 10% of maximum dose threshold.
Conclusion:The developed model has been shown to be highly accurate for pre-treatment verification with the new aS1200 imager which does not display support-arm backscatter artefact and has improved dosimetric properties. Further investigation of FFF modes is in progress. The model is currently being evaluated at sites for potential clinical release.
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