Objective To explore the application value of the simple foot immobilization device in radiotherapy for rectal cancer based on the inter-fractional setup error acquired by image-guided technology of cone beam computed tomography (CBCT).

Methods A total of 49 rectal cancer patients received volumetric modulated arc therapy (VMAT) in Zhongshan Hospital, Fudan University from February 2021 to February 2023 were included. Inter-fractional setup errors of each patient were analyzed. Any situation where the inter-fractional setup error exceeded 7 mm in any three-dimensional direction during the inter-fractional treatment course (the first treatment was excluded) was defined as a failed positioning reproducibility. Binary logistic regression was used for independent factor analysis of the failed positioning reproducibility.

Results In the X-axis, Y-axis, and Z-axis directions, the patients’ inter-fractional setup errors were (2.50±1.97) mm, (2.18±1.73) mm, and (1.17±1.06) mm, respectively. Age (OR＝0.880, 95%CI 0.801-0.967, P＝0.008) and radiotherapy mode (OR＝0.178, 95% CI 0.034-0.936, P＝0.042) were independent factors affecting failed positioning reproducibility. The area under the curve (AUC) of age predicting failed positioning reproducibility was 0.780, with an optimal cut-off value of 53.5 years old.

Conclusions The simple foot immobilization device has good inter-fractional setup reproducibility for patients with rectal cancer who received radiotherapy, but it is not recommended for patients younger than 53.5 years with rectal cancer undergoing preoperative radiotherapy.