Two-dimensional and Three-dimensional Image-guided Evaluation of Patient Positioning for Intensity-modulated Radiation Therapy of Head and Neck Cancer

Patient positioning accuracy is critical in radiation therapy, especially in intensity-modulated radiation therapy (IMRT) for head and neck cancer (HNC), as it can affect treatment effectiveness and safety. This retrospective study aimed to evaluate the accuracy of patient positioning techniques and compare the effectiveness of using multiple image-guided (IG) methods for IG-IMRT of HNC. Cone-beam computed tomography (CBCT) and kV-planar imaging (OBI) collected 3240 treatment couch coordinates in three translational directions from 60 HNC patients undergoing IMRT. Inter-fraction errors were assessed by registering the scans to the planning CT, and the population systematic set-up error (Sigma), random error (sigma), and planning target volume (PTV) margin were calculated. The results between OBI and CBCT were analyzed and compared using one-way ANOVA. The findings demonstrated that more than 80% of the image-guided patient positioning set-ups were acceptable. The mean couch displacement for image-guided techniques was negligible in all translational directions using OBI and CBCT. However, the PTV margin for both methods was more than 0.5 cm, except for the CBCTA-P direction. This study highlights the effectiveness of OBI and CBCT as modalities for evaluating and improving the accuracy of IMRT in HNC patients. Determination of the systematic and random errors and calculating the optimal PTV margin without rematching images can help improve the precision of patient positioning and ultimately lead to better treatment outcomes.