ESTRO 2024 - Abstract Book

S4100

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

In total, 108 observer markers were defined and analyzed. The absolute differences in identified center position of the implanted fiducial markers between the observers and the clinically used positions are presented in Figure 1 for anatomical directions left-right (LR), anterior-posterior (AP) and superior-inferior (SI). The median absolute differences from clinical marker positions were 0.15 mm (range: 0.00-0.83 mm) (LR), 0.13 mm (range: 0.00-1.69 mm) (AP) and 0.85 mm (range: 0.00-3.67 mm) (SI). The largest differences were found in the SI-direction with four observations (3.7%) above 2.5mm (one slice thickness) and 23 observations (21.3%) above one half of the slice thickness (1.25 mm) (Figure 1).

The four largest deviations belonged to the same patient and were found for all observers. The median deviation between observer and clinical marker position was 1.13 mm, 0.64 mm, 0.94 mm and 0.79 mm for observers A, B, C and D respectively (Kruskal-Wallis p=0.1). In Figure 2 the absolute distance between observer and clinical marker position for the nine patients are presented. Patients 7, 8 and 9 had absolute deviations larger than 2.5 mm. The observers noted the marker identification of patient 8 to be particularly difficult.