S2158
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
Results: All 20 test patients were successfully emulated using the template-based VMAT adaptive workflow without major manual edits. The entire adaptive process, including AI segmentation, plan adaptation, and dose calculation, was completed in an average of 15.6 ± 3.6 minutes per patient, enabling same-day treatment initiation. All adapted plans met predefined dosimetric goals for target coverage and OAR constraints.Heart Dose Metrics by Laterality:V1.5Gy: Left = 27.5 ± 6.9%, Right = 19.2 ± 5.3%V3Gy: Left = 5.8 ± 1.9%, Right = 2.5 ± 1.0%V7Gy: Left = 1.0 ± 0.9%, Right = 0%Ipsilateral Lung Dose: V8Gy = 12.3±0.5%AI-generated PTVs demonstrated high concordance with physician contours, achieving a DSC of 0.91 ± 0.02. Only minor manual adjustments were required, primarily at the lateral and medial borders and along the superior– inferior extent.
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Feasibility of Adaptive Sequential SBRT Planning for a PSA Response–Adapted Salvage Radiotherapy Trial (RANGER): Preliminary DVH Analysis Aurelie Garant, Neil B Desai, Daniel Yang, Akrita Bhatnagar, Xingzhe Li, Raquibul Hannan, Ruiqi Li, Zohaib Iqbal, Mu-Han Lin, David Parsons Radiation Oncology, UT Southwestern Medical Center, Dallas, USA
Purpose/Objective: Biochemical failure of prostate cancer after
prostatectomy is commonly treated with prostate fossa radiotherapy, often without imaging-defined disease localization. While intensification with pelvic nodal radiotherapy (PNRT) and androgen deprivation therapy (ADT) can improve outcomes, it also increases toxicity. Prior studies suggest that patients who demonstrate a PSA response at 5 weeks post-fossa RT may not benefit from such intensification, supporting a response-adapted approach. In the RANGER Phase II trial, all patients receive 32.5 Gy SBRT to the prostate fossa. Only “non-responders” with insufficient PSA decline proceed to receive PNRT (25 Gy in 5 fractions) and 4 months of ADT, with nodal plans pre-matched to
the fossa treatment. Material/Methods:
Five emulated salvage radiotherapy cases were planned using an online adaptive CBCT-based workflow (Ethos™, Varian, a Siemens Healthineers company, Palo Alto, CA). Each case included initial fossa SBRT and a potential nodal SBRT boost. Match- line separations of 6, 8, 10, 12, and 14 mm between fossa and nodal planning target volumes (PTVs) were tested to determine the minimal gap that avoids underdosage or overdosage at the junction. Plans were assessed for PTV coverage (volume receiving prescription dose), organ-at-risk doses, and junction hotspots. Protocol constraints required ≥ 95% of each PTV to receive the full dose, with a maximum dose of <115% of 32.5 Gy. Results: An 8 mm PTV gap was found to be optimal. At this separation, prostate fossa PTV coverage exceeded 98% (all plans ≥ 98.2%), and pelvic nodal PTV coverage exceeded 95% (mean ~97.3%; lowest 95.9%). Clinical target volume (CTV) coverage was consistently excellent, with >97.5% of both fossa and nodal CTVs receiving the full dose. Junction hotspots remained within acceptable limits (Dmax ~39 Gy), and organ-at- risk doses, including those to the bladder and rectum, met all protocol constraints. These findings confirm that sequential SBRT fields with an 8 mm gap can be delivered safely and effectively. The Ethos™ adaptive workflow enabled precise daily alignment, maintaining the planned gap and mitigating anatomical variability.
Conclusion: Direct-to-treatment ultra-hypofractionated breast radiotherapy using VMAT is clinically feasible and can dramatically shorten the consultation-to-treatment interval from weeks to hours, improving patient convenience and reducing treatment-related stress. A single template plan can be adapted across patients efficiently without compromising plan quality. Future AI refinements tailored to institutional contouring standards may further enhance automation and streamline clinical workflows. References: 1Murray Brunt et al. The Lancet, 2020, 395(10237), 1613-26 Keywords: direct-to-treatment, ultra-hypofractionated breast
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