S67
Brachytherapy - Gynaecology
ESTRO 2026
source activity cohorts [LC: 90.7% (95% CI: 82.9-92.5%) vs 90.8% (95% CI: 86.3 - 95.3%) p=0.95]. The 3-year DFS and OS rates were also similar between the two groups (p value: 0.55 and 0.54, respectively) (Figure 1). On multi-variable analysis, HRCTV volume and number of concurrent chemotherapy cycles emerged as significant factors for local control (p values 0.03 and 0.01, respectively), whereas source activity (either binary or linear variable) had no significant impact on local control (HR 0.942, p=0.75) (Table 1). Late grade ≥ 3 gastrointestinal (GI) and genitourinary toxicities (GU) (CTCAE V5) were also comparable (14.8% vs 12.8%, p = 0.70; 4.9% vs 4.5%, p = 0.88, respectively).
and prospect of two decades of evolution within the GEC-ESTRO GYN working group and the EMBRACE studies. Radiother Oncol. 2018;126(3):421- 428. Stenhouse K, et al. Prospective application of an artificial intelligence decision-support tool for applicator and needle selection in cervical brachytherapy. Int J Radiat Oncol Biol Phys. 2023;117(3):547-555.Kajikawa T, et al. A machine learning-based decision support tool for needle selection in cervical brachytherapy. Brachytherapy. 2025;24(2):123-130. Impact of Iridium Source Decay on outcomes of Image-Guided Brachytherapy for locally advanced cervical cancer Arunima Nagar, Supriya Chopra, Asesh Samanta, Prachi Mittal, Ankita Gupta, Jeevanshu Jain, Satish Kohle, Yogesh Ghadi, Reena Phurailatpam, Prachi Sawant, Jai Prakash Agarwal Radiation Oncology and Medical Physics, Tata Memorial Hospital, Mumbai, India Digital Poster 2566 Purpose/Objective: Concurrent chemo-radiotherapy (CTRT) and high-dose rate image-guided brachytherapy (HDR-IGBT) is the standard treatment for locally advanced cervical cancer (LACC). Given the relative rapid decay of Iridium192 (half-life 73.8 days), reduced source activity leads to an increased treatment time and may potentially have impact on biologically equivalent dose1 and possibly on local control2. This study evaluated the impact of HDR source activity on long- term clinical outcomes and adverse events. Material/Methods: This single-centre study included patients with FIGO 2018 stage IB2 - IVALACC treated with image-guided intracavitary ± interstitial BT (IC ± ISBT) from 2018- 2022. The planning objectives followed the GEC-ESTRO recommendations3.Impact of known prognostic and predictive variables on clinical outcomes, with an additional variable for source activity decay, both as a continuous and a categorical variable (dichotomized into low (<3 Ci) and high ( ≥ 3 Ci) source activity groups was used for for comparative analysis. Statistical analyses were performed using SPSS v25. Results: A total of 240 patients (median age 53 years) were included; 47% had FIGO 2014 stage IIB disease and 45% had AJCC T3b-T4a local disease. Overall, 46.5% patients were node positive (FIGO 2018 stage IIIC1-2). The median source activity was 4.49 Ci (Range: 1.34 - 9.87 Ci). At a median follow-up of 39 months (IQR: 35.21 - 42.58 months), there was no significant difference in 3-year local control between low and high
Conclusion: Our results suggest that variation in source activity strength during IGABT did not impact outcomes in the present cohort, with equivalent tumour control observed at a lower dose rate when no correction was applied. These results are reassuring for centres facing delays in source replacement. However, further studies are warranted in larger cohorts to validate this finding. Keywords: Brachytherapy, source decay, cervical cancer References: 1. Bi S, Zhou J, Xu M, et al. Reevaluating BED in cervical cancer HDR brachytherapy: source decay and tissue- specific repair significantly impact radiobiological
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