ESTRO 2021 Abstract Book

S827

ESTRO 2021

Conclusion PD-L1 positivity in TILs was found to be associated with lower acute radiation toxicity in terms of oral mucositis and dysphagia in oropharyngeal carcinoma treated with definitive chemo-radiotherapy. This could serve as a potential biomarker for predicting acute radiation toxicities in these cohort of patients. The impact of PDL1 positivity in TILs on treatment response needs further research in studies with larger sample size. PO-0995 Locally advanced nasopharyngeal carcinoma treated with a mixed beam (photons-protons) radiotherapy. I. Turturici 1 , G. Marvaso 1,2 , D. Alterio 1 , E. D'Ippolito 3 , B. Vischioni 4 , S. Ronchi 4 , M. Bonora 4 , V. Vitolo 4 , E. Mastella 5 , G. Magro 5 , P. Franco 6 , M. Krengli 7 , P. Fossati 8 , R. Ricotti 9 , S. Gandini 10 , S. Comi 11 , A.M. Camarda 1 , E. La Rocca 1 , S. Volpe 1,2 , M. Tagliabue 12 , E. Verri 13 , E. Orlandi 4 , B.A. Jereczek-Fossa 1,2 , R. Orecchia 14 1 IEO European Institute of Oncology IRCCS, Division of Radiation Oncology, Milan, Italy; 2 University of Milan, Department of Oncology and Hemato-Oncology, Milan, Italy; 3 Istituto Nazionale Tumori IRCCS Fondazione G. Pascale, Vision of Radiation Oncology, Napoli, Italy; 4 Centro Nazionale di Adroterapia Oncologica, Clinical Radiotherapy Unit, Pavia, Italy; 5 Centro Nazionale di Adroterapia Oncologica, Medical Physics Unit, Pavia, Italy; 6 University of Turin, Department of Radiation Oncology, Torino, Italy; 7 University of Piemonte Orientale, Department of Translation Medicine, Radiotherapy Unit, Novara, Italy; 8 MedAustron Center for Ion Therapy and Research, Medical Department, Wiener, Austria; 9 Centro Nazionale di Adroterapia Oncologica, Clinical Department-Bioengineering Unit, Pavia, Italy; 10 IEO European Institute of Oncology IRCCS, Epidemiology and Biostatistics Unit, Milan, Italy; 11 IEO European Institute of Oncology IRCCS, Unit of Medical Physics, Milan, Italy; 12 IEO European Institute of Oncology IRCCS, Division of Head and Neck Surgery, Milan, Italy; 13 IEO European Institute of Oncology IRCCS, Division of Urogenital and Head and Neck Tumors, Milan, Italy; 14 IEO European Institute of Oncology IRCCS, Scientific Directorate, Milan, Italy Purpose or Objective To evaluate oncological and toxicity outcome of patients (pts) with locally advanced nasopharyngeal cancer (LANPC) treated with a sequential mixed beam (MB) approach (Intensity Modulated Radiotherapy -IMRT- followed by Proton therapy). Materials and Methods Patients treated with MB (IMRT up to a total dose of 54-60 Gy followed by proton therapy up to a total dose of 70-74 Gy RBE -Relative Biological Effectiveness) between June 2012 to December 2019 were included in the analysis. Clinical outcome (in terms of local control -LC-, -year local relapse free- -LRFS-, distant metastases free- survival -DMFS-) and toxicity profile were evaluated. The Common Terminology Criteria of Adverse Events (CTCAE v4.0) were used for acute and late toxicity reporting. Results Forty-six pts with LANPC (cT3-4, N0-N3, M0, according to AJCC 8 th edition) have been analyzed. All patients underwent concomitant CT. The overall time treatment was of 57 days. After a median follow-up of 34 months, LC was 93% (n=41), 2-year LRFS and DMFS were 92% and 82% respectively. Although stage III represented 50% (n=24) and stage 50% (n=24) of cases, LC control was not statistically different between the two groups (P=0.29 and P=0.95, respectively). No differences were observed between the groups regardless of induction CT (P=0.93 and P=0.47, respectively). Despite the significantly high doses prescribed in the MB protocol, toxicity profiles were acceptable with