Image Fusion System Applied to the Evaluation and Correction of Patient Position During Radiotherapy

Radiotherapy planning is traditionally based on computed tomography (CT) images taken from the target areas, which are then analyzed in order to determine the radiation dosage and beam forms. The treatment efficiency then depends on one’s ability, when applying the radiation, to reproduce the position in which the patient stood when the CT images were taken. In this paper, we describe an image fusion procedure that helps the radiotherapy physicians to compare the patient’s current position to that of the CT sessions, and then to estimate the positioning errors and the needed correction displacements. The system is currently under evaluation at the University of Brasilia’s Hospital, where a digital radiographic image (check film) is taken from each patient at the moment of the radiographic session. The check film is then fused with a digitally reconstructed radiography, using the proposed approach and allowing positioning corrections. Our preliminary results suggest an improvement, even without an electronic portal image device, of patients’ positioning with respect to the pure visual analysis, by the physicians, of the two separate images. In the next stage of the research, we will use a larger sample in order to determine the statistical significance of the observed differences.