S437
Clinical - Gynaecological
ESTRO 2026
acute and late toxicity outcomes of daily CBCT-based oART with weekly MRI guidance during definitive chemoradiotherapy. Material/Methods: From May 2023 to November 2023 five patients (128 fractions) with locally advanced cervical cancer (FIGO IIB/IIIB) were treated with the ETHOS radiotherapy device. This is a subgroup analysis of the prospective MARS trial.2 All patients received daily CBCT-based oART (45-50.4 Gy in 25-28 fractions) with weekly MRIs, followed by brachytherapy (28 Gy in 4 fractions). Concurrent platinum-based chemotherapy was administered weekly. Target delineation was adapted according to the Radiation Therapy Oncology Group. Due to daily plan adaption, a reduced PTV margin of 5 mm was used. To compare dosimetric parameters of the oART plan and the scheduled plan a paired t-test analysis was performed. Acute (<90 days after RT completion) and late toxicities (two years after RT completion) were assessed using CTCAE (v.5.0). Results: In all 128 fractions, the adapted plan was superior as judged by the dose-volume- histogram. PTV coverage was evaluated using the dose parameters D95% (target: ≥ 171 cGy per fraction) and V95% (target: ≥ 95%). The adapted plan met these requirements significantly more often than the scheduled plan (99.4% vs 42.4% of all fractions; p < 0.0001). Mean difference in D95% was -15.3 cGy (95% CI -19.6 to -11.0 cGy) per fraction, and -3.9% (95% CI -4.4 to -3.3%) for V95% (Figure 1). Furthermore, a significant dose reduction to OARs (rectum and bladder) was achieved (Figure 2). Acute bowel, rectum and genitourinary tolerance was favourable, with only one patient experiencing ≥ grade 2 toxicity (cystitis, hematuria). Only one patient reported grade 2 late toxicity (rectal prolapse).
Conclusion: Daily oART for locally advanced cervical cancer significantly improves target coverage. Minimizing radiation dose to OARs contributes to favorable quality of life outcomes and low rates of long-term toxicity. These findings are encouraging and have prompted initiation of AIM-C1 trial, a prospective single-arm phase II study evaluating oART in cervical cancer.3 References: 1. Lorusso, D., et al. Pembrolizumab or placebo with chemoradiotherapy followed by pembrolizumab or placebo for newly diagnosed, high-risk, locally advanced cervical cancer (ENGOT-cx11/GOG-3047/KEYNOTE- A18): a randomised, double-blind, phase 3 clinical trial. The Lancet 403, 1341-1350 (2024).2. Kim, J.Y., et al. Clinical Workflow of Cone Beam Computer Tomography-Based Daily Online Adaptive Radiotherapy with
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