S1690
Physics - Detectors, dose measurement and phantoms
ESTRO 2026
scatter exposure – device 0.5 cm outside a 15 × 15 cm² field, and (ii) in-field exposure – device at isocentre (Figure 2). Fractionation schemes reflected clinical practice: 40.05 Gy/15 fx and 26 Gy/5 fx (adjuvant breast RT – moderate and ultra-hypofractionation), 60 Gy/8 fx (SBRT – central tumours), 27 Gy/3 fx (SBRT – peripheral tumours), and cumulative doses up to 200 Gy (reirradiation). After each fraction or dose step, device function and battery voltage were verified using a Medtronic 2090 programmer for resets, errors, or mode changes.
Nevertheless, confirmation in clinical settings is essential to fully establish their safety and guide patient management in real-world practice. References: 1. El-Chami MF, Garweg C, Clementy N, et al. Leadless pacemakers at 5-year follow-up: The Micra Transcatheter Pacing System Post-Approval Registry. Eur Heart J. 2024;45(14):1241-1251. 2. Serbetci YA, Jaryal S, Bhasin I, Elhassan M, Muslim A, Aquilini P, et al. Pacemakers in modern cardiology and their transition from traditional to leadless models. Cureus. 2025;17(2):e82182.3. Kempa M, Mitkowski P, Kowalski O, et al. Expert opinion of a Working Group on Leadless Pacing. Kardiol Pol. 2021;79(5):604- 608.4.Martínez Sande JL, García Seara J, Rodríguez Mañero M. Radiotherapy in a leadless pacemaker. Europace. 2018;20(1):81. Keywords: leadless pacemaker; Micra™; radiotherapy safety; Prompt gamma ray and fast neutron spectroscopy for in-vivo proton range verification and tissue composition characterization Anna M Bekkevoll 1,2 , Kristian S Ytre-Hauge 2 , Sander B Thu 2 , Ilker Meric 3 , Toni Kögler 4,5 , Liv B Hysing 1,2 , Camilla H Stokkevåg 1,2 1 The Cancer Clinic, Haukeland University Hospital, Bergen, Norway. 2 Department of Physics and Technology, University of Bergen, Bergen, Norway. 3 Department of Computer Science, Electrical Engineering and Mathematical Sciences, Western Norway University of Applied Sciences, Bergen, Norway. 4 OncoRay–National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany. 5 Helmholtz-Zentrum Dresden - Rossendorf, Institute of Radiooncology OncoRay, Dresden, Germany Purpose/Objective: Proton beam range uncertainties arising from anatomical variations, imaging, and patient setup may result in deviations from the planned dose Digital Poster Highlight 4599 distribution, necessitating the use of safety margins and thereby reducing the therapeutic advantage of proton therapy [1]. To this end, we are developing a compact detector array consisting of organic scintillator bars with dual-ended light readout, enabling simultaneous detection and imaging of prompt gamma rays (PGs) and fast neutrons (FNs). This novel dual-particle approach has the potential to enhance counting statistics and thereby improve the monitoring precision of the proton beam range,
Figure 1. (1A) Chest CT showing the Micra™ pacemaker (arrow) anchored in the right ventricle. (1B) Device positioned within a PMMA phantom with water- equivalent bolus simulating soft tissue.
Figure 2. Schematic of the phantom setup: (2A) Micra™ 0.5 cm outside, (2B) within the field. The phantom comprised PMMA slabs with a bolus layer; dashed and shaded areas denote the field edge and treatment field. Results: Across all irradiation protocols, including high single- fraction doses (≥ 5 Gy), high dose rates (up to 2400 MU/min), and cumulative in-field doses of 200 Gy, no device malfunctions, resets, or error messages were detected. Battery voltage changes did not exceed 0.02 V (≤ 0.6 % of baseline) and showed no cumulative decline. Devices with partially depleted batteries demonstrated identical stability to those with near-full charge. Even under photon energies of 10 MV FFF, conditions where conventional CIEDs frequently exhibit transient errors, the Micra™ pacemakers maintained full functional integrity. Conclusion:
Leadless Micra™ pacemakers demonstrated remarkable resistance to ionizing radiation, maintaining complete functionality during
conventional, hypofractionated, and stereotactic RT. While this phantom-based study did not include direct pacing performance assessment, our findings indicate that with meticulous dosimetric planning and appropriate monitoring, Micra™ leadless pacemakers can remain safely in place during photon radiotherapy across a broad range of clinically relevant scenarios.
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