ESTRO 2024 - Abstract Book

S3989

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Daily 4DCBT-based dose accumulation in adaptive 4D lung SBRT

Laura Büttgen 1 , Thilo Sentker 2,3 , Rene Werner 2,3 , Tobias Gauer 1

1 University Medical Center Hamburg-Eppendorf, Clinic for Radiotherapy and Radiation Oncology, Hamburg, Germany. 2 University Medical Center Hamburg-Eppendorf, Institute for Applied Medical Informatics, Hamburg, Germany. 3 University Medical Center Hamburg-Eppendorf, Instidtute for Computational Neuroscience, Hamburg, Germany

Purpose/Objective:

In adaptive 4D lung SBRT, daily treatment planning using 4DCBCT simultaneously accounts for both anatomical changes and tumor motion variations. However, it remains unclear how interfractional tumor motion variations impact the dose application process. This study performs dose accumulation for SBRT lung patients using (1) the initial planning CTs (i.e., 4DCT, no additional tumor motion information) and (2) the corresponding daily 4DCBCTs (i.e. consideration of interfractional tumor motion changes) to quantify potential target dose alternations.

Material/Methods:

Out of 73 SBRT lung patients with both 10-phase planning 4DCT (Siemens AS Open) and 10-phase pre-treatment 4DCBCT (Varian TrueBeam v2.7), a representative cohort was selected for retrospective fraction-wise dose accumulation. Regression-based correspondence models, that correlate patient-specific internal motion (i.e., vector fields yielded by deformable image registration) and external breathing signals, were built for (1) the initial planning 4DCT and (2) fraction-wise 4DCBCT. Subsequently, dose accumulation was performed by predicting the internal motion (i.e., vector fields) based on the external breathing signal acquired during treatment and then employing the respective vector field to transform the temporally corresponding VMAT dose segments (cf. figure 1). For analysis, accumulated 4D doses were compared per fraction and in total (5 fractions) with the initially planned 3D dose of the PTV. PTV coverage was quantified by the percentage difference between planned D 98%,plan and accumulated doses D 98%,4DCT and D 98%,4DCBCT

Results: