S50
Brachytherapy - Gynaecology
ESTRO 2026
References: Mahantshetty U, Poetter R, Beriwal S, Grover S, Lavanya G, Rai B, et al. IBS–GEC ESTRO–ABS recommendations for CT-based contouring in image- guided adaptive brachytherapy for cervical cancer. Radiother Oncol. 2021;160:273–284.
demonstrated promising accuracy, with deviations at the needle tip remaining below 1.3 mm. Conclusion: Both proposed methods demonstrated their feasibility in preclinical studies, indicating their potential to enhance and streamline future clinical implantation workflows through improved needle navigation. Keywords: brachytherapy, needle navigation, image guidance Implementation of Intraoperative Mobile CBCT for Enhanced Needle Placement in Cervical Cancer Brachytherapy Andre Karius, Vratislav Strnad, Christoph Bert, Rainer Fietkau, Stefanie Corradini, Claudia Schweizer, Ricarda Merten Radiation Oncology, Strahlenklinik, Erlangen, Germany Purpose/Objective: Accurate needle placement is essential in cervical cancer brachytherapy to ensure optimal tumor irradiation while minimizing dose to surrounding organs. Conventional ultrasound guidance can be limited in visualizing deep pelvic regions, potentially compromising implant quality. We developed a workflow incorporating intraoperative mobile cone- beam computed tomography (CBCT) alongside ultrasound to overcome these limitations. Material/Methods: The workflow was implemented in 26 consecutive patients. CBCT provided 3D visualization of needle positions in real time, enabling immediate correction if deviations were detected. Image quality was assessed based on applicator detectability and tissue contrast- Digital Poster Highlight 953 to-noise ratio. Needle placement was analyzed by enhanced insertion depth (EID) and proximity of needle tips to target borders. Dosimetric impact on the tumor and organs at risk (OARs) was evaluated by comparing CBCT-guided implants with historical ultrasound-only procedures and simulated scenarios. Implant reproducibility was assessed through registration of intra- and postoperative imaging. Results: Incorporating CBCT slightly increased procedure time but improved operator confidence and perceived safety. Needles were inserted deeper and more accurately into the pelvis (mean EID 14 ± 11 mm), resulting in better tumor coverage and reduced exposure of OARs. Dosimetric analysis confirmed improved target dosing while optimizing also the dose to healthy tissues (tradeoff increase up to 5 Gy). CBCT images showed adequate quality for both intraoperative guidance and subsequent treatment planning.
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Needle Navigation in Interstitial Brachytherapy: Combining Infrared Tracking and Radiography for Real-Time Implantation Guidance Andre Karius, Veronika Kreß, Ricarda Merten, Vratislav Strnad, Rainer Fietkau, Stefanie Corradini, Christoph Bert Radiation Oncology, Strahlenklinik, Erlangen, Germany Purpose/Objective: Intraoperative cone-beam computed tomography (CBCT) offers accurate three-dimensional guidance for applicator placement in gynecologic brachytherapy but involves additional radiation exposure and longer procedure times. To reduce the number of verification scans required, this work presents two complementary methods for needle path navigation, including real-time correction of potential bending. The approach integrates infrared tracking with planar X-ray imaging to achieve precise intraoperative needle guidance. Material/Methods: A 200 mm brachytherapy needle was securely attached to an infrared-reflective tracking tool to enable real-time positional tracking. Two planar X-ray images acquired from distinct viewing angles were used in addition to the information about the distal needle end taken from the tracking to determine the precise three-dimensional location of the needle tip through backprojection. A spline was then fitted to the reconstructed coordinates to model the complete needle trajectory. Based on this reconstruction, only a single initial CBCT scan was required to visualize the predicted needle path within the corresponding volume. In addition, a second prediction approach was introduced that relied on a single planar X-ray image, utilizing prior information about needle bending obtained from the initial CBCT scan. Both techniques were evaluated in preclinical experiments and validated against CBCT-derived ground truth. Results: The proposed method utilizing two planar X-ray images successfully reconstructed the needle trajectory with deviations of less than 1 mm compared to the CBCT reference, provided that an angular offset of at least 20° between the X-ray acquisitions was
applied. The single-image approach, which incorporated prior bending information, also
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