ESTRO 2020 Abstract Book

S1010 ESTRO 2020

Results A biologically-relevant parameter space has been identified in which, to a first approximation, FLASH radiation depletes sufficient oxygen for a transient hypoxic response. An example case for three model parameters is given in Figure 1.

between 1981 and 2017. Patients were treated by surgery alone (n=65), surgery followed by PORT (n=56) or primary radiotherapy (RT, n=6) alone. Furthermore, CD8+ TIL and PD-L1 status was assessed via immunohistochemistry (IHC) for a subset of n=84 patients. IHC data analysis was performed by QuPath Software V0.2.0 (Belfast, Northern Ireland). Clinico-pathological characteristics and immune marker expression were correlated with progression-free and overall survival (PFS, OS). Results For a total of 127 patients median age was 61 years. 54% were male and 72% of the tumors were localized in the parotid gland. Of the 13 occurring tumor histologies within this cohort, the three most frequent were adenocarcinoma (NOS, 24%), adenoid cystic carcinoma (19%) and mucoepidermoid carcinoma (17%). High overall CD8+ and PD-L1 tumor infiltration was associated with higher age (p=0.016, p=0.040) and the histological tumor subtype (p=0.005, p=0.046). Overall high CD8+ infiltration (OS: p=0.046) and high CD8+ infiltration of the tumor invasive front (OS: p<0.001, PFS: p=0.033) correlated with impaired outcome. For PD-L1, positive staining of ≥5% of the tumor cells was associated with worse OS (p=0.002). Regarding combined CD8+/PD-L1 expression, patients with low overall CD8+ infiltration showed better OS, regardless their PD-L1 status (p=0.004). Conclusion SGC are a heterogeneous group of carcinomas with varying immune infiltration and prognosis. In this retrospective cohort high CD8+ tumor infiltration and high PD-L1 expression were associated with impaired overall survival. These results should be validated in a multicentric cohort. PO-1812 Peripheral immune cells and intraoperative radiation in low-risk breast cancer I. Linares 1 , M.A. Berenguer Frances 1 , R. Cañas-Cortés 2 , M. Pujol-Canadell 2 , M. Nuñez 1 , S. Comas Antón 3 , E. Martinez 4 , M. Laplana 4 , H. Pérez-Montero 4 , M.J. Pla Farnós 5 , B. Both 6 , F. Guedea 1 1 Institut Català d´Oncologia. Institut d’Investigació Biomèdica de Bellvitge IDIBELL, Radiation Oncology. Radiobiology and Cancer Group- ONCOBELL Program, Barcelona, Spain ; 2 Institut d’Investigació Biomèdica de Bellvitge IDIBELL, Radiobiology and Cancer Group- ONCOBELL Program, Barcelona, Spain ; 3 Hospital Germans Trias i Pujol, Radiation Oncology, Badalona, Spain ; 4 Institut Català d´Oncologia, Radiation Oncology, Barcelona, Spain ; 5 Hospital Universitari de Bellvitge, Gynecology Department, Barcelona, Spain ; 6 Medical Technology Business Group- Carl Zeiss Meditec AG- ZEISS Group, Director Medical Affairs & Professional Education- Business Sector Radiotherapy, Oberkochen, Germany Purpose or Objective The purpose of this study was to assess changes in peripheral blood immune cell composition after intraoperative radiation therapy (IORT) on the surgical bed in low-risk breast cancer undergoing conserving breast surgery. Material and Methods Peripheral blood samples from 13 patients were collected preoperatively and at 48 hours and 3 and 10 weeks after IORT in a single dose of 20 Gy. Peripheral B lymphocytes, CD8+ cytotoxic T cells, CD4+ T helper cells, natural killer cells (NK), regulatory T cells (Treg), and myeloid-derived suppressor cells (MDSCs) were determined by flow cytometry. Results The subpopulation of NK CD56 +high CD16+ increased significantly at 3 weeks after IORT (0.30% to 0.42%, p < 0.001). Significant changes in the subpopulation of NK CD65-/CD16+ after treatment with IORT were observed throughout the study period (p = 0.05). There was an increase of CD8+ cytotoxic T cells, with the highest levels

Conclusion Thresholds for a number of parameters, including dose and dose rate, have been determined for a feasible FLASH effect caused by oxygen depletion, which can be used as a starting point for experimental verification. The development of a full mechanistic understanding of the FLASH effect is essential for its translation into a clinical setting. 1. Favaudon et al. Ultrahigh dose-rate FLASH irradiation increases the differential response between normal and tumor tissue in mice. Sci Transl Med, 2014. 6 (245): 245ra93. PO-1811 The prognostic value of CD8+ infiltration and PD-L1 expression in salivary gland cancers N. Kesar 1 , R. Winkelmann 2 , F. Rödel 1 , J. Oppermann 1 , S. Balster 3 , S. Ghanaati 4 , C. Brandts 5 , D. Martin 1 , C. Rödel 1 , P. Balermpas 6 , J. Von der Gruen 1 1 University of Frankfurt, Department of Radiotherapy and Oncology, Frankfurt, Germany ; 2 University of Frankfurt, Dr. Senckenbergisches Institute of Pathology, Frankfurt, Germany ; 3 University of Frankfurt, Department of Otorhinolaryngology, Frankfurt, Germany ; 4 University of Frankfurt, Department of Oral- Maxillofacial and Facial Plastic Surgery, Frankfurt, Germany ; 5 University of Frankfurt, Department of Medicine- Hematology/Oncology, Frankfurt, Germany ; 6 University of Zurich, Department of Radiation Oncology, Zurich, Switzerland Purpose or Objective Salivary gland carcinomas (SGC) account for 1-6% of all head and neck tumors with 20 different histological subtypes. Surgical resection is the standard treatment for SGC, followed by postoperative radiotherapy (PORT) in case of high-risk factors. Exploration of the immunological microenvironment of these tumors could facilitate a more individualized treatment approaches in the future. We examined the prognostic value of CD8+ tumor infiltrating lymphocytes (TIL) and programmed death ligand 1 (PD-L1) expression in a single center patient cohort. Material and Methods We retrospectively analyzed the clinical data of 127 patients treated at the University Hospital of Frankfurt Poster: Radiobiology track: Immuno-radiobiology