Univariate and multivariate analysis of the styrofoam fixation device on patient setup errors in radiotherapy.

Background: Styrofoam is a patient-specific immobilization device in radiotherapy; most previous studies about the impact of styrofoam on setup errors have only analyzed a single tumor type, and have not considered the influence of patient's physical condition on the setup errors of styrofoam.

Purpose: This study aims to evaluate the impact of styrofoam device on setup errors in radiotherapy and explore which patient population is more suitable for styrofoam immobilization.

Methods: Univariate and multivariate analyses were conducted to compare the setup errors between the experimental group (styrofoam combined with thermoplastic mask) and the control group (thermoplastic mask alone). All cases were categorized based on tumor location into head and neck, thorax, abdomen, and limb cases, with age, gender, surgical history, educational level, and body mass index (BMI) serving as variables in the multivariate analysis. Intragroup analysis was also performed.

Results: For all included cases, the experimental group had median setup errors of 1.20 , 2.00 , and 1.30 mm in the vertical, longitudinal, and lateral directions, respectively. In contrast, the control group had median setup errors of 1.50 , 2.00 , and 1.85 mm in the same respective directions. Notably, the experimental group demonstrated statistically significant reductions in average setup errors in the longitudinal direction (2.00  vs. 2.87 mm, p < 0.01) and lateral direction (1.90  vs. 2.24 mm, p < 0.01) compared to the control group. The intragroup analysis results indicated that factors such as age, gender, surgical history, and educational level had no significant impact on the setup errors in the experimental group.

Conclusion: The styrofoam fixation device for patient immobilization can effectively reduce setup errors in both the longitudinal and lateral directions, and the styrofoam fixation device is suitable for most people.