A comparative study of postural fixation techniques for radiotherapy in upper abdominal malignancies

In this study, we investigated the impact of two distinct postural fixation techniques on the incidence of setup errors in patients with upper abdominal malignancies.

Seventy-seven patients with upper abdominal malignancies were divided into two groups: an observation group comprising 31 patients managed with a combination of thermoplastic body film and an air bag, and a control group consisting of 46 patients managed solely with thermoplastic body film. Prior to radiotherapy, a cone-beam computed tomography (CBCT) scan was performed, followed by registration of CBCT scans and positioning computed tomography (CT) images. Setup errors along the X (left/right), Y (superior/inferior), and Z (anterior/posterior) axes of the two groups were recorded and analyzed. A Wilcoxon rank-sum test was used for data analysis. Random errors (Σ), systematic errors (σ), and planning target volume (PTV) margins (MPTV) were evaluated.

The three-directional setup errors of the observation group [X: 1.9 (0.90, 2.73), Y: 2.5 (1.48, 3.7), Z: 1.4 (0.78, 2.3)] and the resultant displacement vector [T: 3.97 (3.08, 5.32)] exhibited lower magnitudes compared to those observed in the control group [X: 2.3 (1.1, 3.6), Y: 3.5 (2.1, 5.4), Z: 1.8 (0.9, 3.1); T: 5.51 (4.18, 7.25)]. These differences were statistically significant (p < 0.05). Notably, the Σ, σ, and MPTV in the observation group were consistently smaller than those observed in the control group.

The combined use of thermoplastic body film and an air bag in postural fixation significantly reduces setup errors during radiotherapy for patients with upper abdominal tumors. This combined approach enhances the precision of postural alignment, thereby improving positional repeatability and reducing both random and systematic errors. Furthermore, this method is associated with decreased planning target volume margins, providing better protection to adjacent normal tissue structures.