S1866
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Conventional workflows rely on dedicated simulation CT (simCT) scans, which often introduce delays, increase patient discomfort, and create logistical challenges. Although sim-free workflows have been explored previously [1,2] they often lack systematic integration and formal risk assessment. To address these gaps, we developed a workflow based solely on diagnostic CT (dCT), eliminating the need for separate simCT sessions and incorporating a structured Failure Mode and Effects Analysis (FMEA) to identify and mitigate potential risks. The primary aims were to reduce overall treatment time (OTT), maintain dosimetric accuracy, and enable a safer, patient- centered approach. Material/Methods: A retrospective dosimetric study assessed the feasibility of dCT-based treatment planning. Deviations in planned dose delivery were evaluated, particularly considering differences in patient positioning between dCT and simCT. For clinical implementation, a centralized coordination platform (RayCare) managed the workflow, including also patient selection, image registration, AI-assisted organ segmentation, and contouring directly on dCT scans (in RayStation). Initial patients also underwent simCT as a contingency. Risk management was addressed via FMEA, systematically evaluating potential failures from patient selection through treatment delivery, and implementing mitigation strategies to ensure safety and reliability. Results: Retrospective analysis revealed up to 15% underdosage in D98% of the planning target volume (PTV) due to positioning discrepancies, which was reduced to a mean deviation of –2.55 ± 3.69% after adjustment, confirming clinical acceptability (Table 1). In the prospective phase, an FMEA identified key risks, leading to fine-tuning of the screening flow, agreements on segmentation, and clear actions for fallback plans. Until now, two patients were managed within the dCT workflow. The first patient achieved perfect patient-specific quality assurance (PSQA) results without increased treatment time. The second patient was excluded due to a linear accelerator DICOM readout error; the pre-prepared simCT backup enabled treatment within 15 minutes. Minimal script modifications demonstrated workflow adaptability and scalability.
optimisation time saving ratios ranged from 1.5-5.3 and an absolute time saving of 4.7- 20.5mins. Dosimetric equivalency for all plans was assessed by a Radiation Oncologist for clinical acceptability. There was no discernible clinically significant difference in dosimetry with capped/non-capped ED curves particularly when the high-density region fell well outside the target region.
Conclusion: Capping the maximum applied electron density was shown to have a direct impact on reducing the optimisation and calculation times of offline and online planning on the MR-Linac. Reducing the time for this critical step significantly improves workflow efficiencies and enhances the user and patient experience. Keywords: electron density, MR-Linac, calculation time Optimizing Palliative Radiotherapy Planning with a Diagnostic CT-Only Workflow: A Clinical Pilot study with Integrated FMEA. Arnaud Colijn, Michaël Claessens, Geert De Kerf Medical Physics, Iridium Network, Antwerp, Belgium Purpose/Objective: Palliative radiotherapy plays a vital role in alleviating symptoms in patients with advanced cancer. Digital Poster 2024
Conclusion: This pilot study demonstrates that a dCT-only radiotherapy workflow is feasible, safe, and clinically
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