S1935
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Keywords: Reference-free, direct-to-unit, adaptive RT
doses were similar.
Digital Poster 3425
Single-plan simultaneous vs. sequential SABR for bilateral adrenal metastases: a dosimetric and workflow efficiency study using MR-guidance Nicolas Giraud 1,2 , Famke L. Schneiders 1 , Suresh Senan 1 , Miguel A. Palacios 1 1 Radiation Oncology, Amsterdam UMC location Vrije Universiteit Amsterdam, Amsterdam, Netherlands. 2 Radiation Oncology, CHU Bordeaux, Bordeaux, France Purpose/Objective: Bilateral adrenal metastases from solid tumors occur in up to 43% of patients during disease evolution1. Bilateral stereotactic ablative radiotherapy (SABR) offers a non-invasive alternative to surgery. Magnetic resonance-guided SABR (MR-SABR), with daily online adaptive replanning, breath-hold gating, and real-time 3D tracking, enables high-dose delivery to both glands. We compared dosimetric and practical aspects of
Spinal cord and vertebral doses were higher with sequential delivery in most plans, while differences in kidney and spleen doses varied by anatomy (Figure 2).
Conclusion: Single-plan MR-SABR for bilateral adrenal metastases significantly improves workflow efficiency, reduces beam-on-time and enhances patient comfort with fewer hospital visits. This approach, however, presents a clear dosimetric trade-off. While sequential plans may achieve higher target coverage, the single-plan strategy offered superior sparing of vertebrae and digestive organs, and also simplified the planning process and dosimetric evaluation by eliminating the complexity of dose accumulation. MR-guided adaptive systems are highly effective for this challenging indication, allowing clinicians to select the optimal strategy based on a patient’s specific anatomy and OAR proximity. References: 1. Mao, J. J., Dages, K. N., Suresh, M. & Bancos, I. Presentation, disease progression and outcomes of adrenal gland metastases. Clin. Endocrinol. (Oxf.)93, 546–554 (2020). Keywords: Bilateral adrenal metastases; MR-linac Impact of Enhanced Leaf Modelling on Low-Dose and Gradient Regions in Halcyon-Based Multi- Metastasis SRT Mark Ashburner, Arun Gandhi, Omer Ali, Ben Scarlet Radiotherapy, Te Whatu Ora Health New Zealand, Waikato, New Zealand Purpose/Objective: Enhanced Leaf Modelling (ELM) in Varian Eclipse v18 provides a refined representation of multileaf collimator (MLC) transmission incorporating the Digital Poster 3437 physical leaf shape, and interleaf leakage for Halcyon, rather than relying on the traditional dosimetric leaf gap parameter. Commissioning at our centre validated
single-plan versus sequential MR-SABR for simultaneous bilateral adrenal metastases. Material/Methods:
From an ethics-approved database, we identified 11 patients treated with MR-SABR for bilateral adrenal metastases (09/2016-05/2025). Patients were originally treated with either a single-plan (55%) or sequential plans (45%). To create a paired, comparative planning study, we retrospectively generated the alternate strategy for each patient (i.e. sequential plans for the single-plan cohort and vice versa). This yielded a complete paired dataset (n=11) for direct comparison. Plans were compared using the original fractionation (5x10/3x15/1x24 Gy) and institutional constraints (e.g. digestive, spinal cord, kidney). Key metrics (Coverage Compromise Index [CCI], monitor units [MU], estimated treatment times) were extracted and compared using Wilcoxon paired tests. Results: The paired analysis of 11 patients showed a significant workflow benefit for the single-plan strategy. Single- plan delivery reduced the total beam delivery time (median 61.8 min vs 79.4 min sequential, p=0.001) and MUs per fraction (median 5622.8 vs 6939.3 with sum of sequential plans, p=0.01). Dosimetrically, sequential delivery achieved a higher median PTV D95% (105.9% vs 97.2%, p=0.04) and trended toward an improved CCI (0.88 vs 0.81, p=0.15). This apparent coverage benefit, however, may be an artifact of summing dose distributions. Doses to digestive organs were often higher with the summed sequential plans. Conversely, single-plan strategies, by using efficient “bridging” MLC segments, occasionally increased intermediate dose spill in the lomboaortic area (Figure 1), though aortic
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