S715
Clinical – Lower GI
ESTRO 2026
2023;5. Valentini V et al. Preop hyperfractionated CRT for recurrent rectal cancer after prior RT: phase II study. Int J Radiat Oncol Biol Phys 2006; Keywords: Recurrent rectal cancer, MRIgRT, Reirradiation
(40%), for 28 adapted fractions out of 366 (7.7%), mainly due to interfractional variations in bowel or bladder filling, improving target coverage and OAR sparing. The ORR was 25% (CR 10%, PR 15%) and the DCR 55%. Three patients (15%) were successfully converted to radical surgery after MRIgRT. At a median follow-up of 5 months, median LC was 8 months, with LC rates of 54.5%, 31.1%, and 15.6% at 6, 12, and 24 months, respectively. Median PFS and OS were 5 and 19.1 months, with 12- and 24-month OS rates of 74.1% and 28.8%. Patient and treatment characteristics are summarized in Table 1.
Mini-Oral 2676
Prospective evaluation of longitudinal measurements of HPV ctDNA during chemoradiotherapy for anal squamous cell carcinoma Daniel Martin 1,2 , Eva Heger 3 , Ulrike Wieland 3 , Markus Diefenhardt 1,2 , Maximilian Fleischmann 1 , Emmanouil Fokas 4 , Claus Rödel 1,2 , Franz Rödel 1,2 1 Department of Radiation Oncology, University Hospital Johann Wolfgang Goethe University, Frankfurt, Germany. 2 Frankfurt Cancer Institute, FCI, Frankfurt, Germany. 3 Institute of Virology, National Reference Center for Papilloma- and Polyomaviruses, Faculty of Medicine and University Hospital Cologne, University of Cologne, Cologne, Germany. 4 Department of Radiation Oncology, Cyberknife and Radiotherapy, Center for Integrated Oncology Aachen Bonn Cologne Duesseldorf (CIO ABCD), University of Cologne, Faculty of Medicine and University Hospital of Cologne, Cologne, Germany Purpose/Objective: Definitive chemoradiotherapy (CRT) is the current standard treatment for localized anal squamous cell carcinoma (ASCC). Nevertheless, locoregional recurrences and/or distant metastases still occur and are associated with potential high morbidity due to salvage surgery or dismal prognosis due to ineffective systemic treatment options. The objective of this study, was to evaluate monitoring of human papillomavirus (HPV) circulating tumor DNA (ctDNA) levels during CRT. Material/Methods: 53 patients with histologically confirmed, ASCC were treated with standard CRT. Blood samples were collected at baseline, at the end of treatment, and during the first follow up visit. HPV16 ctDNA levels were quantified using digital PCR. This study was approved by the local ethic committee and all patients provided written consent. Results: 51% (27/53) of patients showed measurable ctDNA at baseline (median 8 copies/ml; range 0 – 25322 copies/ml; IQR 0 – 84 copies/ml).Gross Tumor Volume (GTV) correlated significantly with baseline ctDNA load (R = 0,5; p < 0.001) and baseline ctDNA load was associated with an increased risk for development of distant metastases (HR for increments of 100 copies/ml: 1,011 [95% CI: 1.002 – 1.021]; p = 0.021).
Conclusion: MRI-guided reirradiation for LRRC is feasible, safe, and well tolerated, achieving encouraging local control with minimal toxicity and allowing surgical conversion in selected cases. Prospective studies with larger cohorts and longer follow-up are warranted to validate these findings and refine patient selection criteria. References: 1. Georgiou PA et al. Diagnostic accuracy of MRI in planning pelvic exenteration for advanced colorectal cancer. Eur J Cancer 2013;2. Gambacorta MA et al. Radiotherapy & total neoadjuvant therapy for recurrent rectal cancer (RETRY). Radiat Oncol 2024;3. Gani C, Boldrini L, Valentini V. Online MR-guided radiotherapy for rectal cancer. Clin Transl Radiat Oncol 2019;4. Mantello G et al. Modern techniques in re- irradiation for LRRC: systematic review. Cancers
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