margins of planning target volume and set-up errors based on megavoltage cone-beam ct image guided radiotherapy with helical tomotherapy: importance of automatic registration plus manual registration

Background: helical tomotherapy (ht) enables daily verification of patient positioning using megavoltage computed tomography (mvct) during each treatment session.objective: the present study aimed to investigate the effects of automatic registration (ar) compared to a combination of automatic and manual registration (ar+mr) on setup errors. additionally, the study aimed to determine the corresponding margins of the planning target volume (mptv).material and methods: in this experimental study, a total of 1513 daily mvct scans were analyzed from september 2020 to january 2024, which were obtained from 71 patients diagnosed with head and neck (hn), cervical, and gastrointestinal cancer. the scans were registered with the planning ct to determine the setup errors of the patients. the analysis compares the setup errors between the ar and the ar+mr techniques in translational (x, y, and z axes) and rotational directions (rx, ry, and rz). additionally, the study calculated the mptv.results: in the ar and ar+mr techniques, the translational setup errors were significantly different in the z-axis for hn patients. for cervical cancer patients, ar and ar+mr exhibited significantly different translational errors across all axes. furthermore, they also had notable differences in the y and z-axis translational errors for gastro-intestinal (gi) patients. regarding the rotational setup errors, a substantial difference was observed in the z-axis translational error for cervical cancer patients, and in the y and z-axes for gi patients. conclusion: human assessment after automatic registration helps ensure that the registration is clinically appropriate, especially in circumstances involving deformable patient anatomy.