22. Feasibility study for the implementation of aS1000 EPID controls of RapidArc® treatments using FFF photon beams

Introduction The development of VMAT (Volumetric Modulated Arc Therapy) treatments by flattening filter free photon beams (FFF) involves the adaptation of dosimetric verification methods. A number of physical limits (detector saturation, backscattering…) or algorithmic limits, constrain us to use 3D phantoms of which implementation is time-consuming. In order to optimize the patient workflow, the purpose of this study concerns the technical feasibility of using the EPID (Electronic Portal Imaging Device) and the performances of the algorithms PDIP (Varian) and GlAaS (EPIQA) for the verification of plans of treatment Varian RapidArc® FFF. Methods The chain of treatment includes a Varian Clinac 2100C accelerator with an EPID aS1000 imager and the PDIP algorithm V13.6 and EPIQA V2.2.1. A calibration of the portal imager is performed for the energy X6 FFF. To test the criticality of the two algorithms for the local and global gamma index validation methods at 3% 3 mm, the results obtained with the portal imager are compared with those obtained with the ArcCheck. Results The first results show the feasibility of implementing FFF treatment plan validation checks with EPID for CLINAC 2100C accelerators equipped with the aS1000 portal imaging system. Conclusions This study makes it possible to validate the control of the RapidArc® treatment plans by FFF beams using the portal imager. This method is an alternative to 3D phantom validations such as ArcCheck, Delta 4.