S70
Brachytherapy - Gynaecology
ESTRO 2026
sample size precludes the definition of an exact clinical dose–volume threshold. Further research with a larger patient cohort, inclusion of baseline data, and prospective toxicity scoring is necessary to confirm this relationship and to develop evidence-based and clinically relevant dose constraints. Keywords: urethra, toxicity, dose-response References: 1. Spampinato S, Tanderup K, Marinovskij E, Axelsen S, Pedersen EM, Pötter R, et al. MRI-based contouring of functional sub-structures of the lower urinary tract in gynaecological radiotherapy. Radiother Oncol [Internet]. 2020;145:117–24. Digital Poster 3080 Dosimetric and Clinical Efficacy Evaluation of Freehand and 3D-PT-Assisted HDR-ISBT for Central Pelvic Recurrent Gynecologic Malignancies Post-RT Min Li, Weijuan Jiang, xiuwen Deng, Haitao Sun, Junjie Wang, Ping Jiang, Ang Qu Department of Radiation Oncology, Peking University Third Hospital, Beijing, China Purpose/Objective: To compare dosimetric parameters and clinical outcomes of 3D-printed templates(3D-PT) guided versus freehand High-dose-rate (HDR) interstitial brachytherapy (ISBT) in patients with central pelvic recurrent gynecologic malignancies post radiotherapy (RT). Material/Methods: We retrospectively analyzed 27 patients with central pelvic recurrent gynecologic malignancies treated with HDR-ISBT from Jan 2018 to Dec 2023 (3D-PT: n=16; freehand: n=11). Primary endpoints were dosimetric differences, objective response rate (ORR), and local progression-free survival (LPFS). Secondary endpoints were overall survival (OS) and treatment-related toxicities. Results: The 3D-PT group achieved higher HR-CTV D90 and V100 than the freehand group. The variability of the difference between HR-CTV D90 and the prescribed dose (both expressed in EQD2) was significantly lower in the 3D-PT group. There were no significant differences between the 3D-PT and freehand groups in ORR, LPFS, or OS. In the entire cohort, the 1-, 3-, and 5-year LPFS rates were 51.2%, 35.8%, and 23.9%, respectively, and the 1-, 3-, and 5-year OS rates were 95.2%, 63.5%, and 63.5%, respectively. Multivariate analysis revealed that adjacent organ invasion and no objective response were independent adverse prognostic factors for LPFS. No grade ≥ 3 acute toxicities were observed. Grade ≥ 3 late toxicities occurred in 18.8% (3/16) in the 3D-PT group and 36.4%
Radboudumc in 2021–2022, were selected. A standardized T2-weighted MRI urethra contouring protocol was developed, based on Spampinato et al.1, with additional input from an experienced radiation oncologist (CGV) and radiologist (MJMP). Various dose- volume parameters (D0.1cc, D1cc, mean dose) were calculated using the LQ-model with α / β 3. We decided to use the D1cc for this analysis, as a parameter that would reliably reflect the highest urethral dose without being too sensitive for delineation uncertainties. Urethral toxicity was assessed using the Common Terminology Criteria for Adverse Events CTCAE 5.0 through structured telephone interviews conducted by the treating radiation oncologist. For each patient, the highest reported grade of urethral toxicity was included in the analysis. A correlation analysis was performed using Spearman’s rank correlation coefficient to assess the relationship. Results: An MRI-based atlas for contouring the urethra was developed (Figure1). Figure 1: MRI-based atlas for contouring the urethra. Mean urethral volume was 5.5 cc (range 2.8-7.6). The measured EQD2( α / β 3) D1cc brachytherapy dose to the urethra ranged from 9.9 Gy to 76.92 Gy. All patients had also received 25 x 1.8 Gy by external beam radiotherapy, resulting in an additional 43.2 Gy (EQD2 α / β 3) to the urethra (Cumulative dose 53.1- 120.1 Gy). Spearman’s rank correlation analysis demonstrated a correlation coefficient of 0.756 with a p-value of 0.011Figure 2: Correlation between EQD2 and urethral toxicity.
Conclusion: A strong positive correlation (r=0.756, p=0.011) was found between EQD2 doses and urethral toxicity in patients undergoing brachytherapy for gynecological cancer with extensive vaginal involvement. We think that in this group of patients restraining the dose to the urethra might be especially useful. These findings are based on parameters derived from a standardized delineation protocol, which is essential for the reproducibility of dose-volume effects. The small
Made with FlippingBook - Share PDF online