ESTRO 2024 - Abstract Book

S5614

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

ESTRO 2024

A highly precise and reproducible patient set-up is essential in SABR due to the high dose to the target, rapid dose fall-off beyond the target and a small number of fractions. Reviewing the extent of inter-fractional set up errors in patients treated with SABR with inform development of immobilisation and image guided radiotherapy (IGRT) protocols. This study aims to quantify the magnitude of initial kV-orthogonal setup errors in patients treated with lung stereotactic ablative body radiotherapy (SABR) and to identify factors contributing to setup errors and their effect.

Material/Methods:

Patients treated with lung SABR were retrospectively analysed from a single institution. kV-orthogonal images were assessed for each patient in six degrees of motion to determine the magnitude of the initial bony anatomy set-up error (Figure 1). Patient factors, including gender, age, performance status and tumour location, were assessed using univariant analysis.

Results:

Twenty-one patients were analysed in this study. The median setup errors include translational errors; vertical 0.43cm (0.2-0.7cm), longitudinal 0.36cm (0.1-0.7cm), lateral 0.28cm (0.1-0.5cm) and rotational errors: pitch 0.8° (0.3-1.9°), roll 0.5°(0.2-1.0°) and yaw 0.8° (0.3-1.5°) (Figure 2). Univariate analysis of setup errors revealed statistical associations between gender, tumour type/location and being over 75 years.