[Quality control of a kV cone beam computed tomography imaging system]

This work presents the introduction of a quality assurance program for the On-Board Imager (OBI, Varian) kVCBCT system, together with the results of 1 year monthly testing.

Firstly the geometric precision and stability of the equipment and of the associated software were evaluated using the Marker phantom. The coincidence of the accelerator isocenter and the imager isocenter was verified as well as the accuracy of the registration of kVCBCT with reference CT images. Then, the kVCBCT image quality was evaluated using the Catphan 504 phantom and ArtiScan software (Aquilab) for both full-fan (FF) and half-fan (HF) imaging modes.

The kVCBCT isocenter and image registration with correction of the table position were found to be within a tolerance of 2.0mm. Concerning the kVCBCT image quality, image noise and uniformity, the Hounsfield units (HU) stability and linearity, geometric distorsion and high contrast resolution were all found to be within the manufacturer's recommendations for both FF and HF modes. However, the low contrast resolution for the HF mode did not meet the manufacturer's specifications.

The quality assurance tests introduced have defined the initial system characteristics and their evolution during a period of 1 year, demonstrating the stability of the OBI.