Comparison between manual and automatic image registration in image-guided radiation therapy using megavoltage cone-beam computed tomography with an imaging beam line for prostate cancer

This study aimed to compare and assess the compatibility of the bone-structure-based manual and maximization of mutual information (MMI)-algorithm-based automatic image registration using megavoltage cone-beam computed tomography (MV-CBCT) images acquired with an imaging beam line. A total of 1163 MV-CBCT images from 30 prostate cancer patients were retrospectively analyzed. The differences between setup errors in three directions (left–right, LR; superior–inferior, SI; anterior–posterior, AP) of both registration methods were investigated. Pearson’s correlation coefficients (r) and Bland–Altman agreements were evaluated. Agreements were defined by a bias close to zero and 95% limits of agreement (LoA) less than ± 3 mm. The cumulative frequencies of the absolute differences between the two registration methods were calculated to assess the distributions of the setup error differences. There were significant differences (p 3-mm differences. The MMI-algorithm-based automatic registration is not compatible with the bone-structure-based manual registration and should not be used alone for prostate cancer.