ESTRO 2023 - Abstract Book

S607

Monday 15 May 2023

ESTRO 2023

Results The mean duration of the investigated intrafraction motion traces was 25 min [range: 14-44 min]. The fit accuracy was in general best for the augmented quadratic model (ECM 3, Fig 1.b). Cases with a simple linear correlation between internal and external motion were well described by all ECMs (Fig 2, column 1). For cases with hysteresis, augmented ECMs (2,3,4) were needed to fit the data well (Fig 2, column 2), while quadratic ECMs (3-4) were needed for non-linear (banana-shaped) motion (Fig 2, column 3). The best estimation of tumor motion throughout the treatment fractions was obtained with the augmented linear ECM 2, which could account for hysteresis while being more robust against irregular motion than the quadratic ECMs (Fig 1.b). The best ECM update strategy was by regular tumor position sampling every 3s throughout the treatment (Strategies B-C). Conclusion Although the augmented quadratic ECM in general had higher fit accuracy, the augmented linear ECM combined with continuous updates every 3s provided the most accurate tumor position estimation throughout the fraction. This strategy could provide accurate internal motion monitoring based on an external gating camera and sparse 3Hz kV imaging, which is possible at conventional linacs.