S135
Brachytherapy - Physics
ESTRO 2026
DVH parameter addition appears sufficient. However, many DIRs were not acceptable, and future work should focus on developing robust techniques for these challenging cases.Volume and surface-based metrics correlated strongly with qualitative assessment. Surface-based metrics showed potential to better discriminate between groups based on qualitative scores. The visual assessment was limited by reliance on a single rater; future work will incorporate multiple raters to improve reliability. Keywords: Deformable Image Registration, HDR Brachytherapy References: [1] Nesvacil, N, et al. "A multicentre comparison of the dosimetric impact of inter-and intra-fractional anatomical variations in fractionated cervix cancer brachytherapy." Radiotherapy and Oncology 107.1 (2013)[2] Swamidas, J, et al. "Image registration, contour propagation and dose accumulation of external beam and brachytherapy in gynecological radiotherapy." Radiotherapy and Oncology 143 (2020)[3] Weistrand, O, and Svensson, S. "The ANACONDA algorithm for deformable image registration in radiotherapy." Medical physics 42.1 (2015)[4] Brock, Kristy K., et al. "Use of image registration and fusion algorithms and techniques in radiotherapy: Report of the AAPM Radiation Therapy Committee Task Group No. 132." Medical physics 44.7 (2017) Investigation of geometric accuracy of applicator reconstruction in gynaecological brachytherapy using a low-field magnetic resonance scanner Tibor Major 1,2 , Júlia Vizkeleti 1 , Csaba Polgár 1,2 , Zoltán Takácsi-Nagy 1,2 1 Radiotherapy Department, National Institute of Oncology, Budapest, Hungary. 2 Radiotherapy Department, Semmelweis University, Budapest, Hungary Digital Poster Highlight 3116 Purpose/Objective: To quantify the geometric accuracy of applicator reconstruction in gynaecological brachytherapy using low-field magnetic resonance imaging. Material/Methods: A 0.55T MR scanner (MAGNETOM Free.Max, Siemens) has been introduced into brachytherapy treatment planning at our institute. First, interobserver variation in applicator reconstruction was studied. Twenty fractions of eleven patients treated with a Venezia applicator with needles were selected, and five observers determined the tip positions of the applicators/needles. In the tandem and ovoid tubes, MR markers were inserted, but there was only air in
Spearman’s rank test revealed strong negative correlations ( ρ : − 0.71 to − 0.85, p < 0.001) between qualitative scores and quantitative metrics for all structures (figure 1).
Conclusion: ANACONDA demonstrated potential to produce acceptable MR-to-MR DIR for multi-fraction cervical brachytherapy, however most DIR cases scored as acceptable showed <2 Gy EQD2 difference between DIR-DA and DVH parameter addition. In these cases,
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