Évaluation et choix des protocoles d’imagerie sur le système de tomographie conique de basse énergie XVI® d’Elekta

Abstract

PurposeThis work proposes an evaluation of the Elekta XVI® kilovoltage cone-beam computed tomography imaging system. The average dose delivered for each acquisition protocol proposed by default by the manufacturer was measured with several detectors and compared to theoretical dose values given by Elekta. At the same time, an evaluation of image quality for pelvic protocols correlated to dose measurements in homogeneous and heterogeneous mediums allowed to optimize the use of the XVI® system. Materials and methodsThe dose was measured for each acquisition protocol (varying filters, FOV and collimations) with four detectors (CT pencil ion chamber, 0.3 and 0.125cm3 cylindrical ion chambers, radiothermoluminescent dosimeters) in a CTDI phantom. The dose evaluation in a heterogeneous medium was performed in an experimental anthropomorphic phantom simulating a male pelvis. Image quality was assessed with a Catphan® 600 phantom. ResultsThe average dose measured in a homogeneous medium was about 17mGy and 25mGy per acquisition for Pelvis and Prostate protocols and about 17mGy and 1mGy for Lung and Head protocols. The study performed with different detectors showed that doses obtained were of the same order of magnitude (±10%) and agreed with those supplied by the manufacturer. The evaluation of image quality correlated to the average dose measured allowed to optimize the use of XVI® acquisition protocols. Measurement results in a heterogeneous medium showed a dose decrease by a factor 1.5 for bone and by a factor 2 for titanium. ConclusionThe study showed that theoretical values proposed by the manufacturer could be used to estimate the average dose delivered to the patient by the kV-CBCT imaging system. The analysis of all the results led to the implementation of a procedure allowing to optimize and account for the dose delivered to the patient by the CBCT imaging system and to report it in the patient folder.