Evaluation of the acquisition protocols of the XVI elekta imaging system

Abstract

Introduction The use of kV-CBCT for patient positioning during radiotherapy treatments requires the evaluation of acquisition protocols proposed by the manufacturer. Optimization of protocols consists in adapting the kV-CBCT acquisitions according to both patient size and treatment localization, in order to obtain sufficient image quality while minimizing the dose to the patient. The aim of this study is to evaluate the image quality and to measure the dose for each acquisition protocols proposed by the XVI ELEKTA system. Material and methods The image quality is evaluated using the Catphan 600. For each protocol, a comparison of the CT number uniformity, the geometric distortion, the low contrast resolution and the high contrast spatial resolution is performed. The CBDIw is measured using a UNFORS CT chamber and an PTW 0.3 cc ionization chamber. In our institution, the kV-CBCT acquisitions are mainly used for prostate localizations. Thermoluminescent measurements are then performed to compare the dose delivered in the prostate and the femoral heads. Results The pelvis and prostate are the first protocols evaluated. The results show that the prostate protocol is more irradiating than the pelvis with a CBDIw equal to 2.8 cGy against 1.8 cGy for the pelvis. In terms of image quality, the results show no significant differences. The CT number homogeneity is equal to 2.6% for prostate and 2.4% for pelvis protocol. For the low contrast resolution, we obtain values of 1.5% and 1.4% respectively for prostate and pelvis protocols. The high contrast spatial resolution is very low for both, with only 2 lp/cm. No geometric distortion is detected. We are studying the other protocols. Conclusion With the results of this study, we want to extend the use of kV-CBCT to other locations than prostate IMRT and to increase the number of kV-CBCT acquisitons during IMRT treatments.