The importance of precise patient positioning in image guided radiotherapy: retrospective evaluation of estimated irradiation by registered daily cone-beam computed tomography images

Maximisation of irradiation accuracy of malignant tissues is a key challenge on the way to optimal radiotherapy. Strategies to improve irradiation accuracy should balance the expected clinical benefit against the feasibility and procedural demands of the method used. This pilot study marks an initial step toward retrospectively evaluating patient positioning accuracy, analysing CBCT images in relation to clinical outcomes, and estimating actual irradiation of target and surrounding tissues. The CBCT images were acquired from head and neck patients treated with the Halcyon V3.1 linear accelerator. The algorithms for precise alignment of images, which made it possible to estimate the detailed changes in tumour tissue density during treatment sessions were developed in the MATLAB. The recalculation of the actual dose showed that even small positioning errors can lead to significant changes in the delivered dose, especially in areas where critical organs are affected.