ESTRO 2024 - Abstract Book

S5869

RTT - Service evaluation, quality assurance and risk management

ESTRO 2024

performed using the Plan_WL calculated on the CTsim_350 and CTsim_450 scans. In these two cases, PVA resampled the CTsim and the online CBCT images to a slice thickness of 1.4 mm and 1.8 mm, respectively.

For each WL plan/CTsim combination, 20 deliveries were performed using different initial phantom setups to simulate intentional misalignments. All 3D CTsim-CBCT registrations were performed by an experienced radiotherapy technologist in order to avoid inter-observer variability. His intra-observed variability was assessed by repeating 10 CTsim-CBCT registrations for a specific WL test. The results of the Max 2D CAX-BB distances obtained using the CTsim_350 and CTsim_450 were compared with the corresponding values reported with the CTsim_ref. A paired 2-tailed Student's t-tests were used and a significance level of 0.05.

Results:

The Max 2D CAX-BB distances (mean ± SD) were 0.94 mm ± 0.12 mm, 0.84 mm ± 0.13 mm (p < 0.001) and 1.09 mm ± 0.24 mm (p < 0.01) for the CTsim_ref, CTsim_350 and CTsim_450. Respect to the CTsim_ref scenario, the significant differences found in Max 2D CAX-BB distances were compatibles with the intra-observer variability of 0.26 mm (SD) found in this study.

Fig 2 shows how the maximum allowable SRS tolerance of 1.0 mm (AAPM Report No. 54. Report of Task Group 42) is clearly overpassed with the CTsim_450 scan.

Conclusion: