ESTRO 2025 - Abstract Book

S1007

Clinical – Head & neck

ESTRO 2025

better survival after ICT treatment compared to those with distant metastasis. We look forward to more real-world studies to provide more information on the treatment situation and efficacy.

Keywords: EBV-Negative, NPC, immunotherapy

1991

Digital Poster Safe variation from the “5+5” expansion rule for the delineation of primary tumor clinical target volume (CTV-P) in oropharyngeal cancer Viola Salvestrini 1 , Carlotta Becherini 1 , Margherita Zani 2 , Isacco Desideri 1 , Olga Ruggieri 3 , Lucia Pia Ciccone 1 , Beatrice Bettazzi 1 , Dorutina Cela 1 , Emanuela Olmetto 1 , Vieri Scotti 1 , Stefania Pallotta 2 , Lorenzo Livi 1 , Pierluigi Bonomo 1 1 Radiation Oncology, Azienda Ospedaliero Universitaria Careggi, Università di Firenze, Florence, Italy. 2 Medical Physics Unit, Azienda Ospedaliero Universitaria Careggi, Università di Firenze, Florence, Italy. 3 Radiation Oncology, University of Rome "Tor Vergata", Rome, Italy Purpose/Objective: The “5+5” expansion rule for primary tumor clinical target volume (CTV-P) was recommended by international consensus guidelines [1] Figure 1 . Since 2015, our institutional standard of practice (SoP) for oropharyngeal cancer (OPC) patients was based on the omission of 10 mm margin expansion from gross tumor volume (GTV) of the primary tumor (CTV-P2). The purpose of this prospective, single-center, cohort study is to assess the pattern of failure and long-term survival outcomes of OPC patients treated with the omission of CTV-P2. Material/Methods: An isotropic expansion of 5-mm margin was added to GTV in order to generate the CTV-P1, edited for air cavities and anatomical barriers. The PTV-P1 consisted of a 3-mm expansion of CTV-P1. The treatment was delivered by IMRT-SIB Tomotherapy technique with 3-dose level prescription: high, intermediate and low risk PTVs received 6996, 5940 and 5280 cGy in 33 fractions, respectively. Concurrent cisplatin-based chemotherapy was prescribed. A CTV-P2 expanded by 3 mm (PTV-P2) was retrospectively delineated by 3 radiation oncologists, blinded to the clinical outcome data. Survival outcomes were assessed by the Kaplan-Meier method. A Mann Whitney test was applied to analyse the correlations between oral mucositis, PTV-P2 95% coverage (PTV-P2D95) and mean dose to the oral cavity (OralCavity_Dmean).