ESTRO 2025 - Abstract Book

S2921

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Conclusion: Our study highlights the impact of delivery uncertainties on the temperature distribution during microwave hyperthermia treatments for H&N cancer. Using PCE models, we quantified the sensitivity of treatment delivery to parameter variations, observing significant deviations in target temperatures under realistic error scenarios. These findings highlight the need to accurately characterize tissue properties and minimize patient positioning errors during hyperthermia treatment planning and delivery.

Keywords: Hyperthermia, Uncertainties, Head&Neck

References: [1]

G. M. Verduijn et al. , "Deep hyperthermia with the HYPERcollar system combined with irradiation for advanced head and neck carcinoma – a feasibility study," International Journal of Hyperthermia, doi: 10.1080/02656736.2018.1454610 vol. 34, no. 7, pp. 994-1001, 2018/10/03 2018, doi: 10.1080/02656736.2018.1454610. [2] M. Kroesen et al. , "Feasibility, SAR Distribution, and Clinical Outcome upon Reirradiation and Deep Hyperthermia Using the Hypercollar3D in Head and Neck Cancer Patients," Cancers , vol. 13 , doi: 10.3390/cancers13236149.

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Poster Discussion Magnetically confined mega-voltage photon mini-beam radiotherapy Annalisa Walpen 1 , Werner Volken 1 , Chengchen Zhu 1 , Marco F. M. Stampanoni 2 , Peter Manser 1 , Michael K. Fix 1 , Florian Amstutz 1 1 Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland. 2 Institute for Biomedical Engineering, ETH Zürich, and Paul Scherrer Institute (PSI), Villigen, Switzerland Purpose/Objective: Mini-beam radiotherapy, as part of spatially fractionated radiotherapy, emerged as a promising strategy to achieve high tumor control while reducing normal tissue toxicity. The limiting factor for mega-voltage (MV) photon mini beams is the lateral scattering of secondary electrons, contributing to the substantial washing out of the dose pattern. This study’s objective is to investigate the effects of inline magnetic fields on the dose distributions of MV photon mini-beams, aiming to confine secondary electrons and enhancing the peak-to-valley dose ratio (PVDR). Material/Methods: A mini-beam configuration of beam width of 1.0 mm and center-to-center spacing of 5.0 mm at distance 100 cm from the source was used. The impact of inline magnetic fields up to 15 T was evaluated through simulations conducted using the EGSnrc Monte Carlo transport code [1] on a computational phantom (water box). These simulations encompassed mono-energetic photon beams of 2.5-18 MeV. Subsequent investigations were conducted using a Varian Truebeam 6 MV and Ethos 6 MV spectra. A comparison was conducted between an ideal slit beam and a realistic beam including simulation through a tungsten collimator positioned 5 cm above the phantom’s surface. The investigations were extended to two clinically motivated brain cases. Results: PVDR for a 6 MeV beam in water for different magnetic field strengths are shown in Figure 1 as a function of depth and example dose distributions in Figure 2. The PVDR was increased from 2.2±0.1 to 47.1±3.7 at 14 cm depth in water for increasing magnetic fields, while for the Truebeam 6 MV spectrum an increase from 4.5±0.2 to 33.4±3.2 was observed. The PVDR enhancement occurred along the full beam path for all investigated beam energies. The