Determination of patient setup error in radiotherapy using feature-based multimodal rigid image registration

Accurate patient positioning is one of the major requirements of delivering precise radiation therapy. The objective of this research is to verify the localisation of the dose delivered. In this paper, image registration technique based on anatomical landmarks of the patient is used to compare the similarity between Digitally Reconstructed Radiograph (DRR) and the digital portal image acquired by Electronic Portal Imaging Device (EPID) and calculation of the setup error for pelvic region using bony landmark points is done. The purpose of this study is to evaluate these registration results on the basis of parameters like mutual information, joint histogram, scatter plot, joint entropy, histogram error, line intensity profile and Structural Similarity Index (SSIM). For the pelvis case, the average Euclidean distance by gold standard is less than 2 mm. Our results were satisfactory and within acceptable limits i.e. the maximum set up error obtained is 1.859 mm.