ESTRO 2025 - Abstract Book

S1028

Clinical – Head & neck

ESTRO 2025

2449

Proffered Paper Postoperative SBRT for Early-Stage Oropharyngeal and Oral Cavity Cancers with High-Risk Margins: the STEREOPOSTOP GORTEC 2017-03 phase 2 trial Julian Biau 1 , Xushan Sun 2 , Xavier Liem 3 , Jean-Christophe Faivre 4 , Pierre Blanchard 5 , Mélanie Doré 6 , Yungan Tao 5 , Florence Huguet 7 , Jean Bourhis 8 , Michel Lapeyre 1 1 Radiotherapy, Centre Jean Perrin, Clermont-Ferrand, France. 2 Radiotherapy, Hôpital Nord Franche Comté, Montbéliard, France. 3 Radiotherapy, Centre Oscar Lambret, Lille, France. 4 Radiotherapy, Institut de Cancérologie de Lorraine, Vandoeuvre les Nancy, France. 5 Radiotherapy, Gustave Roussy, Villejuif, France. 6 Radiotherapy, ICO, Nantes, France. 7 Radiotherapy, Hopital Tenon, Paris, France. 8 Radiotherapy, CHUV, Lausanne, Switzerland Purpose/Objective: The management of early-stage squamous cell carcinomas (SCCs) of the oral cavity (OC) and oropharynx (OP) often includes primary surgery. In cases with high-risk margins and negative neck dissection, limited adjuvant postoperative brachytherapy to the tumor bed is a therapeutic option 1 . Another possible alternative is postoperative SBRT, which is investigated for the first time worldwide in the STEREOPOSTOP-GORTEC trial 2 . Material/Methods: This multicenter, single-arm, phase 2 study was conducted at 18 hospitals within the GORTEC network. Eligible patients were aged 18 years or older, with pT1-2 (AJCC 7 th edition) OCSCC or OPSCC, with one of the following criteria: R1 margin, close margin < 5 mm, or uncertain pathological margin. Patients were pN0 or pN1 (without extracapsular extension) and exhibited no lymphovascular invasion. All participants received 36 Gy SBRT in six fractions over two weeks using VMAT or CyberKnife (CK), targeting the tumor bed. The primary endpoint was late toxicity (CTCAE V4.03, <15%). Secondary endpoints included acute toxicity, local control, regional control, and OS. Results: Between April 2018 and August 2021, 90 patients were included (median follow-up : 24 months).Seventy-four patients (82.2%) had OCSCC. 55 patients (61.1%) had pT2 tumors. All but one patients were pN0. The indications of postoperative SBRT were: 30% R1 margin, 64.4% close margin, and 5.6% uncertain margins. SBRT was delivered using VMAT in 68 patients (76%) and CyberKnife in 22 patients (24%). No grade ≥ 4 radio-induced acute or late toxicities were observed. The most common acute toxicity was mucositis with 55.5% and 29% grade 2 and 3, respectively. Late toxicities were evaluable in 81 patients. Eleven patients (13.6%) had a grade 3 late toxicity: four patients (5%) with transitory soft tissue necrosis, and seven patients (9%) with osteoradionecrosis. CK was associated with a statistically higher rate of grade 3 osteoradionecrosis. Local control rates at 6, 12, and 24 months were 100%, 93%, and 92%, respectively. Seven patients (8%) had a regional recurrence without local recurrence. Six-, 12-, and 24-month OS rates were 100, 93, and 89% respectively, with 3 deaths attributed to the initially treated cancer. Conclusion: Postoperative SBRT targeting the tumor bed in early-stage OCSCC and OPSCC with high-risk margins was evaluated for the first time worldwide in the STEREOPOSTOP GORTEC phase 2 trial 2 and met its primary endpoint. The observed toxicity and efficacy profiles were comparable to existing techniques 3-4 . SBRT to the tumor bed may represent a viable alternative and warrants further investigation.

Keywords: SBRT, OPSCC and OCSCC, high risk margins

References: 1. Mazeron J-J et al. GEC-ESTRO recommendations for brachytherapy for head and neck squamous cell carcinomas. Radiother Oncol 2009;91:150–6.