IMPLEMENTATION OF END TO END QUALITY CONTROL AND EVALUATION OF THE IMPACT OF DEVIATION IN IGRT CLARITY SYSTEM REFERENCE IMAGE RECORD

The Clarity system is an IGRT system that uses ultrasound imaging to locate the target before starting treatment. The objectives of this work were: to implement an END TO END quality control (QC) for the Clarity IGRT system that does not depend on the characterization of the phantom provided by the manufacturer; To evaluate the impact of systematic image registration errors on treatment and the impact of image acquisition used for reference in anatomical conditions different from simulation. The first step was to position the phantom aligned to the simulation room lasers. At this stage, tomographic (CT) and ultrasound (US) images were acquired. To simulate different anatomy, the phantom was shifted 2 cm vertically and a new US image was acquired. In the planning system, the CT origin was defined exactly where the isocenter was located in the phantom, which are the coordinates used as reference in the US image. Imported US images at the Clarity workstation, CT fusions were performed without US deviations and with displacements of 2, 4, 6, 8 and 10 mm on the lateral, 1 and 5 mm on the vertical and 2 and 5 mm in the longitudinal. For all fusions a reference was generated. In the Linear Accelerator (LINAC), the phantom was positioned similar to the simulation. For the QC, the table was displaced by 20 mm in all directions, from vertical, longitudinal and lateral, and verified the corrections suggested by the system. To assess the impact of registration errors, references with errors were selected and their respective corrections analyzed. Finally, with the reference generated from the other US, it was verified which correction the system indicated. The following results were obtained for QC: vertical, 18.9 and 20.7 mm; longitudinal, 21.2 and 18.2 mm; and lateral 19.6 and 19.9 mm. The values obtained for references with fusion errors were: lateral, 2.2, 4.4, 6.5, 8.1 and 10.4 mm; vertical 0.8 and 3.4 mm; longitudinal, 3.1 and 6.1 mm. The image acquired for different anatomical condition presented vertical displacement of 1.2 mm. With the results obtained, the conclusion was that the whole system is calibrated and that QC can be routinely used as an independent test of the Clarity system. It is also possible to state that errors in the fusion of US with CT will be reflected as systematic errors in the corrections suggested in LINAC. Finally, acquiring reference US under conditions other than CT does not generate displacement errors in LINAC.