ESTRO 2025 - Abstract Book

S3297

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

ESTRO 2025

3131

Digital Poster A prototype single-frame x-ray tomosynthesis system for lung SBRT guidance Scott S Hsieh Radiology, Mayo Clinic, Rochester, USA

Purpose/Objective: Thoracic tumors often require motion management for safe ablative radiotherapy. One common strategy is to track the motion of a surrogate marker, such as breathing phase or external chest motion using an infrared camera. However, surrogates are not perfectly predictive, and direct visualization of the tumor itself would be preferred. The purpose of this work is to evaluate one such direct visualization option, single-frame x-ray tomosynthesis (SFXT), using a prototype system in the context of imaging phantoms.

Material/Methods:

SFXT uses multiple x-ray sources in a grid pattern that are activated simultaneously. Prior tomosynthesis systems move the source or strobe multiple sources of a source array to build up a tomosynthesis image over the course of multiple seconds. SFXT uses simultaneous activation to produce an image within a single exposure (e.g., 30 milliseconds). The tradeoff with SFXT is a smaller field of view, which may be acceptable for many SBRT cases. Beams are collimated onto a small field of view (e.g., 5 cm) and diverge to arrive at non-overlapping sectors of a flat panel detector. The detector image is read out, and the sectors are shifted and added together so that anatomy at isocenter is kept in focus while anatomy far from isocenter is blurred out. We constructed a prototype system using 4 sources and imaged a lung phantom at varying exposure levels. The system is intended to be a drop-in improvement for biplane radiography systems that are currently used for guiding cranial ablative radiotherapy, and the source-isocenter distance (200 cm) and isocenter-detector distance (100 cm) were chosen appropriately. Results: The prototype SFXT system improved the contrast of certain tumors that were otherwise obscured by overlapping anatomy such as the spine. To evaluate dose requirements, four circular tumors of varying size (diameters of 3, 5, 8 or 10 mm) were imaged at 80 kV. The 3 mm tumor was difficult to detect at 1 mAs but could be seen above 3 mAs. All other tumors could be seen down to 1 mAs. This implies that hundreds of SFXT images could be acquired during a treatment before reaching the dose of a typical setup CBCT.