ESTRO 2025 - Abstract Book

S4053

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2025

Figure 1. Subgroup stratification summary

Results: Thirty-one patients were included in the current analysis and 135 CBCT scans were analyzed. The results showed that the mean value for 3D vector displacement was 0.75, 0.81 and 1.14 mm for the thoracic, abdominal/pelvic and scapular groups, respectively. No statistically significant differences were found in the mean displacement values between the groups (p = 0.08). In contrast, the rotation analyses showed a significant difference between the groups, with the abdominal/pelvic group having the lowest mean rotation values (between 0.6° and 0.9°) if compared to other subgroups. Conversely, scapular target group had the highest mean rotational values (between 1.5° and 1.6° - Table 1).

Table 1. Translation and rotation shifts (mean ± Standard Deviation) for each subgroup

Conclusion: Results from the current analysis underline that translations and rotations shifts were generally well contained across different anatomical districts. Immobilization cushion provided a significant benefit in terms of rotation for the abdominal/ pelvic group. Regarding the thoracic and scapular regions, there is an unmet need for immobilization improvement to enhance reproducibility. These data provide an important quality assessment of treatment positioning improving the overall reliability of trial results, and concomitantly offer a detailed description of rotational and translational shifts occurring within the framework of a randomized controlled trial. More data will be available after the analysis of the complete sample size (enrollment completed in December 2024).

Keywords: SBRT, Setup error, Immobilization device