S85
Brachytherapy - Gynaecology
ESTRO 2026
D90, HR-CTV D98, and IR-CTV D90, dose increases of >15%,10–15%,5–10%, and<5% were scored as 3, 2, 1, and 0, respectively. For D2cc of bladder, rectum, sigmoid, and bowel, dose reductions of >15%,10– 15%,5–10%, and<5% were scored as 1.5, 1, 0.5, and 0, respectively. The total score represented the overall dosimetric advantage of the 3D-printed plan. Early ctDNA kinetics were analyzed at baseline, week 1, and week 2 during CCRT, classified as decreasing (favorable), fluctuating, or increasing (unfavorable), and correlated with dosimetric benefit to assess ctDNA’s predictive value for 3D-printed applicator selection. Results: The median HR-CTV volume was 20.5 ml and the number of needles was 6 (range3,8). Comparison between the clinical plans and 3D-printed applicator template plans demonstrated significant dosimetric improvements. HR-CTV D90 increased from 901 to 1008 cGy (p<0.001) and HR-CTV D98 from 816 to 873 cGy (p=0.002), indicating enhanced high-risk target coverage. A significant rectal dose reduction was observed (D2cc:532 vs 489 cGy,p=0.003), while changes in IR-CTV D90 (665 vs 644 cGy,p=0.208) and bladder, sigmoid, and bowel D2cc were not statistically significant. The median composite score for the 3D- printed applicator plans compared to the original plans was 5.5 (range1.5-8.5). A significantly higher proportion of patients with unfavorable ctDNA dynamics achieving scores ≥ 5.5, indicating greater dosimetric benefit from 3D-printed applicators. On multivariate logistic regression, a score ≥ 5.5 was independently associated with increased ctDNA risk (OR =15.5, 95%CI 1.7–139.5,p=0.015), while HR-CTV volume was not (OR=1.29,95% CI0.14–11.6,p=0.82).
Conclusion: Early ctDNA dynamics within the first 2 weeks during CCRT may help identify patients who benefit most from patient-specific 3D-printed applicators in 3D- IGABT for LACC. Unfavorable ctDNA kinetics were associated with greater dosimetric gains, supporting ctDNA-guided personalization of brachytherapy. Keywords: ctDNA, 3D-printed applicator, cervical cancer References: Sammouri J et al. Serial genotyping of the human papillomavirus in cervical cancer: An insight into Virome Dynamics during chemoradiation therapy. International Journal of Radiation Oncology*Biology*Physics. 2023 Aug;116(5):1043–54. doi:10.1016/j.ijrobp.2023.02.018Han K et al. Clinical Validation of Human Papilloma Virus Circulating Tumor DNA for Early Detection of Residual Disease After Chemoradiation in Cervical Cancer. Journal of Clinical Oncology. 2023;41(34):3945 - 3956.Segedin B et al. “The Use of 3D Printing Technology in Gynaecological Brachytherapy—A Narrative Review.” Cancers. 2023;15(16):4165.
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