S136
Brachytherapy - Physics
ESTRO 2026
the needles. We then analyzed separately the interobserver differences in determining the positions of the tips. In the second part of our study, we compared the accuracy of needle reconstruction performed using MR and CT images. Seven plastic needles were inserted into three phantoms, which were then scanned with MR and CT. Five observers determined the tips and entry points of the needles on both types of images. The needle lengths and tip coordinates were compared. Differences between observers in determining the coordinates of the tips of Venezia applicator/needles in patients were described with standard deviation (SD). The lengths and tip coordinates of needles in the phantoms calculated on MR and CT images were compared, and the variability was described with SD. Results: The SD of deviations from the mean was smaller with MR markers than without markers (X: 0.17 vs. 0.27 mm, Y: 0.24 vs. 0.46 mm, Z: 0.17 vs. 0.34 mm). Figure 1 shows the variability of data calculated for applicators with markers and needles without markers. Regarding direction, the greatest variability was observed in the Y direction. The mean difference between needle lengths measured on MR and CT images was 1.2 mm, with an SD of 0.80 mm. The mean deviations of the needle tip coordinates from the mean values were less than 0.1 mm in all directions for MR and CT, and the SDs were smaller for MR. A good correlation (R2=0.999) was found between the tip coordinates calculated on MR and CT images (Figure 2). The variability of the tip coordinates measured with both imaging modalities was small, <1mm SD. Conclusion: The geometric accuracy of the 0.55T MR scanner is suitable for the reconstruction of applicators and needles in brachytherapy treatment planning. MR markers allow for greater precision in determining the tips of the applicators. The accuracy of reconstruction using MR images is comparable to that achieved using CT images.
Keywords: MRI, geometric accuracy, catheter reconstruction References:
Haack, S., et al. 2009. Applicator reconstruction in MRI 3D image-based dose planning of brachytherapy for cervical cancer. Radiotherapy and Oncology 91, 187– 193.Qing, K., et al. 2021. The combined use of 2D scout and 3D axial CT images to accurately determine the catheter tips for high-dose-rate brachytherapy plans. J Appl Clin Med Phys 22, 273–278.Major, T., et al. 2024. Brachytherapy Treatment Planning for Cervical Cancer Patients Using a Lower Magnetic Field MR Scanner. https://marketing.webassets.siemens- healthineers.com/3b9e41eefac69d89/f11fec03a796/si emens-healthineers_magnetom- world_MReadings_MR-in- RT_10th_Edition_ESTRO_2024.pdf Commissioning of first Papillon+ in Sweden Sara Bornedal 1 , Maria Persson 1 , Mohammed Ali Ghazal 1,2 , Ricardo Palanco-Zamora 1,2 , Alexander Valdman 3,2 , Åsa Carlsson-Tedgren 1,2 1 Department of Nuclear Medicine and Medical Physics, Karolinska University Hospital, Stockholm, Sweden. 2 Department of Oncology-Pathology, Karolinska Institute, Stockholm, Sweden. 3 Department of Radiation Oncology, Karolinska University Hospital, Stockholm, Sweden Digital Poster 4038 Purpose/Objective: The Papillon+ (Ariane Medical Systems Ltd) is a contact x-ray brachytherapy system utilizing high dose rate 50 kVp x-rays to treat malignancies of the lower rectum, skin and breast within minutes. In 2025, the first Papillon+ was commissioned at our institution (Figure 1) with the purpose of commencing treatment of operable patients with early-stage rectal cancer of the lower rectum, as described in the OPERA [1] trial. Material/Methods: The commissioning measurements executed wereReference dosimetry in accordance with IAEA TRS-398 [2]Output stability in reference position and
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