S2390
Physics - Quality assurance and auditing
ESTRO 2026
new version of the Ethos gives similar QA results as the previous one, confirming good stability and consistency, but without noticeable benefit from the new algorithms. The dose shift found for plans generated in Ethos 1.0 has not changed with the upgraded version of Ethos system, in both versions the measured dose is on average about 1.5% higher than the TPS calculated dose.
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Comparison of dosimetric verification results for treatment plans generated in Ethos 1.0 and Ethos 2.0. Paulina Wesolowska, Joanna Iwanowska-Hanke, Agnieszka Walewska, Anna Paciorkiewicz, Mikolaj Tarchalski, Bartlomiej Sadowski, Marta Fillmann Medical Physics Department, Maria Sk ł odowska-Curie National Research Institute of Oncology, Warsaw, Poland Purpose/Objective: The Ethos 1.0 system was clinically implemented in June 2024 and upgraded to version 2.0 in September 2025. Key updates affecting plan quality include new intelligent optimization engine and enhanced MLC model. The Ethos system was commissioned per manufacturer and international guidelines. As a part of system commissioning, a group of clinical plans for different locations underwent the verification process. This study compares QA results between the two Ethos versions. Material/Methods: Treatment plans for 27 cases (8 prostate, 6 gynecology, 3 bladder, 10 other) were prepared according to clinical protocols. Seventeen IMRT and ten VMAT plans were: generated in Ethos 1.0, generated in Ethos 1.0 and recalculated in 2.0 (new MLC model), generated in Ethos 2.0 (new MLC model and optimization engine). The same CT dataset and contours were used for each case. Two types of phantoms were used for dose measurement: for VMAT plans the Mobius Verification Phantom (MVP, Varian), and for IMRT plans the Solid Water HE (Sun Nuclear). PTW Semiflex 3D ionization chamber (IC) with UnidosE electrometer (PTW) was used. Measurement points were placed in homogeneous high-dose regions. Results: Measured and TPS-calculated doses were compared. The mean dose differences were -1.5% ± 0.8%, -1.6% ± 0.7% and -1.5% ± 0.6%, respectively for plans generated in Ethos 1.0, recalculated in Ethos 2.0 and generated in Ethos 2.0. As shown in Figure 1, most cases give consistent results with few outliers. The results by a treatment technique- VMAT and IMRT- presented in Table 1 show slightly higher deviations for VMAT plans. This might be related with different phantom used for measurements, where IC depth of measurements is generally smaller. Conclusion: The comparison of QA results between Ethos 1.0 and Ethos 2.0 did not show differences between measured and calculated doses. Despite the new MLC model and optimization engine, no improvement in dose accuracy was observed. It can be concluded that the
Figure 1. IC QA verification results.Table 1. The results of the point dose measurements for VMAT and IMRT plans.
Keywords: QA of Ethos plans,
Digital Poster 4097 Independent phase calculation for deep hyperthermia geometrical planning Daniel Frauchiger 1 , Markus Fürstner 1 , Andreas Joosten 1 , Annalisa Walpen 1 , Emanuel Stutz 2 , Peter Manser 1 , Michael Fix 1 1 Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern, Switzerland. 2 Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Inselspital, Bern, Switzerland Purpose/Objective Hyperthermia is increasingly used as an adjunctive treatment in cancer therapy. While in radiotherapy independent dose verification belongs to patient specific QA in hyperthermia such tools for independent phase calculations are rare. In hyperthermia treatment few systems are available to calculate temperature distributions based on patient geometry, e.g. EasyPlan (Medlogix) for a deep hyperthermia device. The system calculates the phases of the electrical fields emitted by the four antennas based on patient-specific dimensions, to superimpose the electric fields at the tumor center
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