Evaluating the influence of the Siemens IGRT carbon fibre tabletop in head and neck IMRT

Abstract

Background and purpose To investigate the impact of a commercial IMRT/IGRT carbon-fibre tabletop in radiotherapy planning optimization and clinical dose distribution. Materials and methods In this investigation the Siemens IGRT carbon fibre tabletop, routinely used for IMRT treatments in our Centre, has been incorporated into the CT volume of 6 IMRT patients. This was done by CT scanning the tabletop and by adding the obtained volume to the clinical dataset, acquired using the standard couch available in our CT scanner. This procedure was tested and validated for the purpose of this study. The radiotherapy plans have been optimized using both the original CT volume and the modified CT volume. Results IMRT optimization with the tabletop included in the clinical volume produced significantly different deliverable plans compared to standard optimized plans which did not include the treatment couch. Differences up to 6%/7% in terms of total number of MU were found in half of the clinical cases. Differences up to 37% in the number of MU per beam were also found. The number of iterations needed to reach an optimal solution also varied between −18% and +25%. Although the DVH analysis produced similar results, due to the fulfilment of the optimization objectives, differences higher than 10% were found in the dose calculated to superficial regions of the body. Conclusions The results of this investigation show that the presence of the carbon fibre tabletop significantly affects the outcome of the beam parameters optimization. We suggest including carbon fibre tabletops into patient treatment planning dose calculation and optimization.