S620
Clinical – Head & neck
ESTRO 2026
Purpose/Objective: This prospective multicenter study evaluated the feasibility, dosimetric impact, and acute toxicity of ¹⁸ F- fluoromisonidazole (FMISO) PET/CT-guided adaptive radiotherapy for selective dose escalation in patients with locally advanced head and neck squamous cell carcinoma (HNSCC). Here, we report on dosimetric feasibility and acute toxicity outcomes. (Study registered at Clinicaltrials.gov. – NCT05348486) Material/Methods: Between May 2022 and September 2024, patients with stage III–IV HNSCC of the oropharynx (p16-negative), larynx, hypopharynx, or oral cavity were prospectively enrolled. All patients underwent baseline FDG PET/CT and FMISO PET/CT before definitive chemoradiotherapy (CRT) or hyperfractionated accelerated radiotherapy (HART). Hypoxic subvolumes (PTV79.2) were delineated using a tumor-to-muscle SUV ratio >1.4 on FMISO PET and escalated to 79.2 Gy in 33 fractions (2.4 Gy/fraction) via a simultaneous integrated boost, while standard targets received 70 Gy (PTV70) and 54 Gy (PTV54). A mid-treatment FMISO PET/CT after the 11th fraction triggered adaptive replanning for ≥ 20% change in PTV79.2 volume or spatial distribution. Acute toxicity in the FMISO-guided cohort was compared with a contemporaneous control group (n = 65) treated with conventional CRT without dose escalation. Results: Forty-five patients received FMISO-guided adaptive radiotherapy. Hypoxic subvolumes were detected in 77% (median 1.6 cm3, IQR 0.2–7.1 cm3). Adaptive replanning was required in 30% of cases due to spatial or volumetric hypoxia changes. The median maximum dose reached 80.8 Gy versus 74.5 Gy in controls (p < 0.001) while maintaining PTV70/54 coverage. Maximum spinal canal and PRV doses were lower in the FMISO arm (35.8 Gy vs. 40.2 Gy, p = 0.020; 40.2 Gy vs. 47.1 Gy, p = 0.001). Grade ≥ 3 dermatitis occurred in 25% vs. 20%, mucositis in 32.5% vs. 23% (p = 0.29), and xerostomia in 2.5% vs. 3.1%. Grade ≥ 3 dysphagia was more frequent with FMISO guidance (37.5% vs. 20%, p = 0.03). No unexpected acute adverse events occurred in the FMISO arm. Conclusion: FMISO PET/CT-guided adaptive radiotherapy was dosimetrically feasible for selective dose escalation to hypoxic tumor subregions in locally advanced HNSCC. Dose escalation maintained target coverage and respected normal-tissue constraints, achieving acceptable acute toxicity and demonstrating the potential clinical utility of biologically adaptive treatment strategies. References: 1. Bentzen SM, Gregoire V. Molecular Imaging–Based Dose Painting: A Novel Paradigm for Radiation Therapy Prescription. Seminars in Radiation Oncology
year LF, RF, and DM rates were 5% (95% CI 3-8), 0.7% (95% CI 0-2), and 1% (95% CI 0-2), respectively. Five- year DFS and OS were 81% (95% CI, 77-86) and 84% (95% CI, 80-89), respectively. Four patients (2 ModAcc- RT; 2 Hypo-RT) developed Grade 3-4 late adverse event: cartilage necrosis (2), laryngeal edema (1), and severe dysphagia (1). In the univariable analysis, GTV volume (p=0.13), anterior commissure involvement (p=0.45), current smoking status (p=0.30), T1b vs T1a (p=0.55), RT regimen (Hypo-RT vs ModAcc-RT, p=0.85), and bolus use (p=0.85) were not associated with LF.
Conclusion: Partial laryngeal IG-IMRT is a safe and effective treatment for T1 glottic cancer. Hypo-RT provides comparable disease control and toxicity outcomes to Mod Acc-RT in selected patients, while offering the advantage of a shorter treatment course. Keywords: Hypofractionation, Shorter course, Partial larynx
Poster Discussion 3369
FMISO PET/CT-guided dose escalation in advanced head and neck cancer: dosimetric feasibility and acute toxicity of prospective multicenter study Tomá š Bla ž ek 1 , Martin Dole ž el 2 , Zuzana Zd ě blová Č ermáková 1 , Jakub Cvek 1 1 Oncology clinic, University Hospital Ostrava, Ostrava, Czech Republic. 2 Oncology clinic, University Hospital Olomouc, Olomouc, Czech Republic
Made with FlippingBook - Share PDF online