Evaluation of the Elekta Synergy concept for patient positioning in image guided radiotherapy

Abstract: Introduction: The Elekta Synergy machine for external beam radiation therapy is equipped with an x-ray tube for on-line kV imaging and correction of the patient setup. The system can provide both 2D and 3D data for image guided radiotherapy (IGRT). Different aspects of the imaging system (called XVI) has been evaluated, such as image quality, flex of the gantry rotation, accuracy for patient setup correction, x-ray tube output and absorbed imaging doses.Material and Methods: The stability in 2D and 3D image quality as well as the mechanical stability during rotation (also called flex) was measured on a weekly basis during a three month period. The stability of the system was studied by imaging a dense sphere positioned at isocenter. The 3D imaging was evaluated with a Catphan® 500 phantom and the 2D imaging with a Leeds phantom. Accuracy in patient setup corrections was evaluated by scanning a pelvis phantom in different locations. Readout from the software was compared to actual translational movements, which were defined by the room laser readouts on rulers mounted on the table-top in the x- y and z-direction. A gold marker matching study was performed using an Alderson/Rando phantom. Finally, both CT dose index (CTDI) and dose measurements with TLDs were performed. The TLDs were placed between the slices of the Alderson/Rando phantom using thin boards of polystyrene.Results: The XVI showed minor long term variations in flex and stable image quality. The accuracy of detecting patient setup-errors based on bony structures was flawless, although matching with respect to gold markers failed. The received effective dose from a pelvis scan was about 11 mSv and for a head-and-neck scan about 0.15 mSv.Conclusions: Even in its early commercial release the XVI system seems capable of detecting 3D setup-errors with a high accuracy. The software needs to be improved, however, to fully incorporate soft-tissue matching.