[Analysis of setup errors and their correlation with clinical factors in image-guided radiotherapy for prostate...

To quantitatively analyze setup errors of 4 immobilization devices in precision radiotherapy for prostate cancer, their accuracy differences, and the factors affecting their setup precisions.

We conducted a retrospective analysis of 240 prostate cancer patients undergoing image-guided radiotherapy at Sun Yat-sen University Cancer Center from May, 2016 to May, 2024. According to the immobilization devices used, the patients were divided into 1.2 m vacuum bag group (n=60), 1.8 m vacuum bag group (n=60), Orfit frame group (n=60), and customized prone board group (n=60). All the patients received pre-treatment cone-beam CT (CBCT) scans, and setup errors in the right-left (RL), superior-inferior (SI), and anterior-posterior (AP) directions were obtained through XVI system grayscale registration. Further subgroup analyses were performed based on patient stratifications by lymph node irradiation status (n=120 each), age (<65 years, n=80; ≥65 years, n=160), and BMI (BMI<24 kg/m², n=120; BMI≥24 kg/m², n=120).

The setup errors differed significantly among the 4 groups in three-dimensional directions (P<0.05). The customized prone board group showed minimal errors in the RL (0.02±0.25 cm) and SI (0.01±0.32 cm) directions, but demonstrated the largest error in the AP direction (-0.28±0.36 cm). The patients with lymph node irradiation had significantly greater AP directional errors (-0.22±0.36 cm) than those without (-0.01±0.43 cm; P<0.001). BMI showed a negative correlation with SI directional errors (R=-0.45, P<0.001), while age was not significantly correlated with the setup errors (P>0.05).

The customized prone board demonstrates clinically significant advantages for its high setup accuracies in RL and SI directions in spite of its systematic AP directional errors. The setup accuracy in the SI direction is especially important for patients with lymph node irradiation or low BMI. Our findings provide quantitative evidence for immobilization device selection and individualized optimization of precision radiotherapy for prostate cancer.