ESTRO 2023 - Abstract Book

S691

Monday 15 May 2023

ESTRO 2023

group with the level of perfusion dropping rapidly between 1 and 8 days post irradiation. Pimonidazole staining demonstrated much reduced levels of hypoxia in the irradiated group, returning to levels in the control group approximately 8 days post irradiation. Irradiation induced blood vessel maturation as assessed via pericyte coverage and activation for migration of T cells as assessed via ICAM-1. CD8+ and regulatory T cell infiltration increased due to irradiation, with their ratio >1 and increasing with time from irradiation. Radiotherapy increased the expression of genes associated with inflammatory response and creation of an immunologically “hot” TME. Immune deconvolution from bulk RNA sequencing also revealed cytotoxic T cell infiltration peaked 4 days post radiotherapy. Conclusion A radiotherapy dose fractionation of 2Gy x 5 daily doses improved the blood vessel structure and perfusion of a solid tumour environment. Hypoxia was reduced and T cell infiltration increased, with TME changes showing strong and rapid temporal variations. Increased gene expression and enriched gene sets associated with inflammatory responses suggest the low-dose fractionated radiotherapy was able to remodel the tumour vessels and inflame the tumour microenvironment, with the potential to improve immunotherapy efficacy. PD-0821 Serum and saliva cytokines in mice after fractionated radiotherapy of the head and neck region O. Zlygosteva 1 , I. Solgård Juvkam 2 , H.C. Aass 3 , H. Galtung 2 , T. Søland 2,4 , E. Malinen 1,5 , N. Frederike Jeppesen Edin 1 1 University of Oslo, Department of Physics, Oslo, Norway; 2 University of Oslo, Institute of Oral Biology, Oslo, Norway; 3 Oslo University Hospital, Department of Medical Biochemistry, Oslo, Norway; 4 Oslo University Hospital, Department of Pathology, Oslo, Norway; 5 Oslo University Hospital, Department of Medical Physics , Oslo, Norway Purpose or Objective Irradiation of the head & neck (H&N) region may cause a variety of normal tissue damages, and we have established a preclinical mouse model that allows for studying several endpoints (Juvkam et al., 2022). The aim of the present work was to investigate the systemic responses in terms of cytokine expression in serum and saliva and correlate them to macro- and microscopically observed effects. Materials and Methods C57BL/6 female 12-week old mice were randomised to sham treatment or high-dose irradiation of 75 Gy in 10 fractions over 5 days. The radiation field covered the oral cavity, swallowing structures, and salivary glands. Baseline and post-RT investigations included micro- and macroscopic examinations of the skin, oral mucosa and salivary gland as well as blood and saliva collection. Cytokine analysis of serum and saliva was performed with the 12-Plex Luminex Mouse Discovery Assay kit (cat. no.: LXSAMSM-12, Bio-Techne Ltd, Abingdon, UK) and recorded on a Luminex IS 200 instrument (Bio-Rad, Hercules, CA, USA). Cytokines were assessed at baseline and at day 35, 80, and 105 post treatment. Results The analysis detected the following cytokines and chemokines in serum and saliva samples: IL-1 α , IL-6, KC, MIP-1 α , G-CSF, TNF, IL-12 and TIMP-1. Increased levels of IL-1 α in saliva was found on day 35 and 105 after onset of irradiation compared to controls. IL-1a has been reported to activate inflammatory processes as well as to contribute to fibrosis (Cooper et al., 1995). TIMP-1, which has been associated with fibrosis (Ulrich et al., 2003), was also upregulated in saliva samples in the irradiated group on day 35, 80 and 105. In fact, increased fibrotic areas were observed in submandibular glands in the irradiated mice on day 105. TNF was also increased in serum and saliva samples from irradiated group on day 35 and 105. TNF has previously been linked to xerostomia and oral mucositis in H&N cancer patients (Russo et al., 2016). There was a tendency towards an increased level of G-CSF in serum on day 35 in irradiated group. G-CSF is reported to reduce the severity of mucositis in patients after chemotherapy by stimulating the stem cells proliferation (Cooper et al., 1995) which might be a sign of regeneration in oral mucosa. Oral mucositis was indeed found in the irradiated cohort. Conclusion The cytokine profiles of serum and saliva samples from mice were analyzed following fractionated radiation treatment of H&N in the search for biomarkers specific for radiation-induced effects. To our knowledge, no one has previously performed cytokine analyses in mouse saliva after irradiation. Rather early after irradiation (day 35), increased levels of salivary cytokines involved in fibrosis were detected (IL-1 α , TIMP-1), and fibrosis was demonstrated in the salivary glands (day 105). Also, a cytokine involved in stem cell proliferation could point to healing of oral mucositis (G-CSF). The findings may shed light on underlying mechanisms leading to the manifestation of early and late side effects. PD-0822 First evidence of a FLASH sparing effect in human healthy lung samples M. Dubail 1 , C. Lafouasse 2 , S. Lagha 2 , S. Heinrich 1 , V. Favaudon 1 , A. Londoño-Vallejo 1 , M. Lefèvre 2 , N. Girard 2 , M. Dutreix 3 , A. Seguin-Givelet 2 , C. Fouillade 1 1 Institut Curie, UMR3347/U1021, Paris, France; 2 Institut Mutualiste Montsouris, Chirurgie Thoracique, Paris, France; 3 institut Curie, UMR3347/U1021, Paris, France Purpose or Objective Recent developments in FLASH radiotherapy has raised large interest in the radiation community, particularly for its promises to reduce radiation toxicity on healthy tissue without compromising the anti-tumoral effects of radiotherapy (the so-called FLASH effect). Most preclinical FLASH studies have been performed in mice, zebrafish and non-primate mammals but, while the first trials implementing FLASH radiotherapy in the clinic are ongoing, the effect of FLASH in human is still unknown. Previous results from the lab, using an ex vivo lung organotypic slice model recapitulating the complex lung architecture, have shown that FLASH spares cycling cells in mouse lungs 24 hours after irradiation. To provide some first clues, we aimed to use this ex vivo lung model to determine the effect of FLASH radiotherapy in the human lung. Materials and Methods First, we collected human healthy lung samples from lobectomies performed at Institut Mutualiste Montsouris (IMM). Lung samples are sliced and irradiated at a dose of 9 Gy either in conventional or FLASH modes with the ElectronFLASH irradiator