Division of Medical Physics, Department of Radiation Oncology, University Medical Center Freiburg, Freiburg, Germany German Cancer consortium (DKTK), Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg , Germany

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MO-E115-IePD-F7-1 (Monday, 7/11/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: To validate the Monte Carlo (MC) dose calculation algorithm as implemented in Radiance™, version 4.0.8, a dedicated TPS for electron dose calculations in IOERT with a Mobetron intraoperative linear accelerator (linac) by comparing to BEAMnrc built model.

Methods: The MC models were generated using water relative dose measurements. Electron beams of Mobetron linac were collimated by plastic, X-ray imaging compatible, applicators of diameter sizes from 5cm to 9cm. Depth dose curves and dose profiles were compared with 1D gamma analysis in various set-ups of virtual water phantoms with air and bone heterogeneities. 3D image volumes of an anthropomorphic pelvic phantom acquired with a CT scanner (Philips Big Bore CT) and an Imaging Ring CBCT system (medPhoton, Austria) for dose calculations with identical treatment parameters in the two MC systems. A C# script was written to import the EGSnrc output files into Eclipse™ v15.6 TPS and convert them into RT dose files, so that 3D gamma analysis was enabled with the PTW VeriSoft Software v8. 2%/2mm and 3%/3mm gamma criteria with global normalization, were applied for the commissioning of the two beam models and their comparisons respectively.

Results: Commissioning of the BEAMnrc model required optimization of the thickness of the secondary scattering foil. Radiance™ model showed discrepancies with the measured data in surface doses and in the umbra region. Radiance™ underestimated the dose at the field edges of the 6MeV dose profiles with bone inhomogeneity. In air inserts, the computational noise increased, while calculation uncertainties were lower than 1%. In 3D dose comparisons, higher than 90% gamma passing rates were achieved for both imaging systems demonstrating that differences observed in 1D comparisons have no clinical significance.

Conclusion: Radiance™ TPS has a reliable implemented MC algorithm for clinical use in IOERT in the framework of image based treatment planning and delivery.

Keywords

Electron Therapy, Image-guided Therapy, IORT

Taxonomy

TH- External Beam- Electrons: intraoperative

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