S2109
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
Digital Poster Highlight 179
Feasibility of Same-Day Simulation-Free Spatially Fractionated Adaptive Radiotherapy (SF²-ART) Using the Varian Ethos Platform Dennis N Stanley 1 , Alyssa Birchmeier 1 , Carlos E Cardenas 1 , Richard Popple 1 , Natalie Viscariello 1 , Joel Pogue 1 , Courtney Stanley 1 , Mehran Yusuf 1 , Michael Soike 1 , Samuel Marcrom 1 , Joseph Harms 2 1 Radiation Oncology, The University of Alabama at Birmingham, Birmingham, USA. 2 Radiation Oncology, Washington University School of Medicine, St. Louis, USA Purpose/Objective: To evaluate the feasibility and deliverability of a same- day, simulation-free workflow for spatially fractionated adaptive radiotherapy (SF ² -ART) using the Varian Ethos system. Material/Methods: Ten previously treated spatially-fractionated radiotherapy (SFRT) patients (five thoracic, five extremity) were replanned in silico with a Varian Ethos. Phase 1 simulated delivery of 12Gy stereotactic body radiotherapy (SBRT) to a lattice of 1cm spheres and 4Gy to the gross tumor volume (GTV); Phase 2 consisted of four fractions of 4Gy to the GTV. Reference plans were generated from diagnostic CT or CBCT without simulation. Adaptive plans were created on daily CBCT using automated segmentation and rigid lattice propagation. Workflow steps included consultation, imaging, planning, adaptation, and delivery (Figure 1). Deliverability was verified with Mobius3D secondary dose calculation(3%/2 mm).
Results: All ten cases were successfully replanned using the SF ² -ART workflow. Adaptive plans met predefined clinical objectives, with minimal differences compared to clinical plans. Phase 1 dosimetric differences were small ( Δ PTV_High Dmean ≤ 0.5Gy; CI ≤ 0.2), with all OAR
constraints met. All plans passed Mobius3D verification (>90% gamma at 3%/2 mm). GTV
verification showed strong agreement with clinical contours (Dice>0.95; MSD<2 mm). Median total workflow time, including consultation, contouring, adaptive planning, QA, and delivery, was 166 minutes. Timing data and Phase 1 dosimetric comparison metrics are summarized in Table 1. A representative patient example demonstrates lattice generation, adaptive plan quality, and corresponding dose–volume histogram (Figure 2).Table 1 Dosimetry MetricsAverage Δ Min Δ Max Δ PTV_HighDmax0.03cc (Gy)0.160.030.28V12Gy (%)4.000.206.60Dmean (Gy)0.190.020.51V6Gy (%)0.470.001.10Conformity Index 0.050.000.20PTV_LowDmax0.03cc (Gy)0.370.020.83V4Gy(%)2.560.007.00Dmean
Made with FlippingBook - Share PDF online