ESTRO 2024 - Abstract Book

S4276

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

[2] Zachiu, Cornel, et al. "An improved optical flow tracking technique for real-time MR-guided beam therapies in moving organs." Physics in Medicine & Biology 60.23 (2015): 9003.

[3] Borman, P., et al. "OC-0706: First MRI-guided MLC-tracking using a deformable motion phantom." Radiotherapy and Oncology 152 (2020): S397-S398.

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Digital Poster

Clinical experience with free-breathing expiration-gated 10MV FFF VMAT lung SBRT

Isabel F Remmerts de Vries 1 , Max Dahele 1 , Ben J Slotman 1 , Wilko FAR Verbakel 1,2

1 AmsterdamUMC, Radiation oncology, Amsterdam, Netherlands. 2 Varian Medical Systems, Research, Palo alto, USA

Purpose/Objective:

Stereotactic body radiotherapy (SBRT) is often performed in free-breathing, irradiating a 4DCT-derived internal target volume (ITV) to incorporate tumor motion [1,2]. Especially when respiratory-associated tumor motion is substantial, this results in increased doses to lung and organs-at-risk (OAR), potentially increasing toxicity. In addition, more motion can make tumor/OAR boundaries less distinct on a free-breathing (3D) CBCT-scan, especially for example, when the tumor has a low density and is small. This can make set-up image registration more difficult and increase geographic uncertainty (Figure 1). Deep inspiration breath hold (DIBH) may reduce the irradiated lung volume and sharpen the CBCT image, but is not feasible for all lung SBRT patients (many of whom have impaired lung function) and, the tumor position can vary between breath holds [3]. Free-breathing expiration gated (EG) lung SBRT can address these issues and is in routine clinical use in our department. Free breathing removes the burden associated with breath hold, EG (e.g. using phases 30-70% of a 10-phase 4DCT) substantially reduces the ITV and in general, the expiration baseline is relatively reproducible. We evaluated the reduction in longitudinal tumor motion and ITV with EG and report treatment time and intra-fraction EG CBCT-derived shifts during EG lung SBRT.

Figure 1 A: 4D planning CT, B: Non-gated CBCT, C: EG-CBCT. In red the EG PTV

Material/Methods: