ESTRO 2025 - Abstract Book

S3206

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

ESTRO 2025

References: [1] S. Misson-Yates. Optimised conformal total body irradiation: a heterogeneous practice, so where next? Br J Radiol. 2023, 96 [2] E. Seravalli. Treatment robustness of total body irradiation with volumetric modulated arc therapy. Phys Imaging Radiat Oncol. 2024, 29 [3] J.W. Wolthaus. Comparison of different strategies to use four-dimensional computed tomography in treatment planning for lung cancer patients. Int J Radiat Oncol Biol Phys. 2008, 70 [4] C. Zachiu. An improved optical flow tracking technique for real-time MR-guided beam therapies in moving organs. Phys Med Biol. 2015, 60 [5] M. Groot Koerkamp. Automated dose evaluation on daily cone-beam computed tomography for breast cancer patients. Radiother Oncol. 2024, 200 Digital Poster Simultaneous Tracking of prostate and rectum for intrafractional motion management of prostate SBRT Laura Happersett 1 , Sarah Burleson 1 , Hai Pham 1 , Yabo Fu 1 , Himanshu Nagar 2 , Antonio Damato 1 , Pengpeng Zhang 1 1 Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA. 2 Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, USA Purpose/Objective: Intrafractional motion management (IMM) benefits patients who received stereotactic body radiotherapy (SBRT) for prostate cancer by ensuring target coverage and reducing genitourinary and gastrointestinal toxicities (Keall 2017, Neylon 2024). Conventional IMM implemented on an X-ray image-based platform relies on tracking the fiducials implanted inside the prostate, but lacks information on the motion of adjacent organs at risk for the design of a gating strategy and subsequent reconstruction of the delivered dose. We developed a program to simultaneously track the prostate and rectum enhancing the technical capability and potential benefit of IMM. Material/Methods: We utilized imaging data from ten prostate SBRT patients for this retrospective study. Each patient received treatment of volumetric modulated arc therapy, with a prescription dose of 8 Gy × 5 fractions. A hydrogel spacer was injected between the prostate and rectum to reduce the rectal dose. A spacer is visible on kV images providing a reliable motion surrogate of the adjacent rectal wall residing in the high-dose region. During beam delivery, MV-kV image pairs were acquired at every 20º gantry rotation and registered to the templates generated from the planning CT. The prostate and rectum were localized by matching the three prostate-implanted fiducials and spacer, respectively (Figure 1). The motion traces were analyzed to characterize prostate and rectal intrafractional motion, utilized to estimate the delivered dose via isocenter shifts, and recorded for quality assurance. 623