ESTRO 2020 Abstract book

S306 ESTRO 2020

parameter is currently analyzed retrospectively by pathologists at both institutions. First radiomic analyses have been undertaken for quality assurance purposes. Radiomics feature analyses and model building will be performed in the upcoming months. Special emphasis will be laid on the differential influence of CT and RT. Discussion: The upcoming results will show if radiomic features can be used as a basis for response prediction in STS patients. However, the prospective models will need to compete with the pathological measure “%VC which is currently used as an endpoint in multiple prospective trials. SP-0519 Evaluation of Motion Mitigation for Abdominal Radiotherapy M. Daly 1 1 University College London Hospitals NHS Trust, Radiotherapy, London, United Kingdom Abstract text Background: Abdominal organ motion must be taking into consideration for delivery of accurate radiotherapy to organs such as the pancreas and biliary tract. There are ways to reduce this, such as the use of an abdominal compression belt or arch to limit respiratory motion, as well as respiratory-correlated 4D scans to quantify motion. Our department does not currently offer abdominal compression, or abdominal SBRT. Methods & materials: A one-week radiation therapy observership was completed at Princess Margaret Hospital in Toronto, Canada during September 2019. The expected areas to be studied included observation of: SBRT treatment delivery for abdominal cancers, SBRT planning methods for abdominal tumours, and respiratory- correlated (4D) CT acquisition. Abdominal compression and other motion mitigation strategies (such as breath hold with Elekta ABC) were also to be observed. The feasibility of implementing similar practices in our home department was to be assessed. Results: Aspects of various parts of the patient pathway were observed. Scanning and planning techniques were observed. The use of both abdominal compression and ABC were observed on the treatment units. At least three patients were observed on treatment for SBRT to the liver. Discussions with specialist radiation therapists (research and education) occurred regarding the host institution's approach to research and staff education. Motion mitigation strategies were selected on a patient-by- patient basis, based on the reduction of motion in that particular case. Conclusion: Implementation of abdominal compression and SBRT is feasible within our home department based on what was learned on this observership. Effective staff education is vital when implementing complex abdominal motion mitigation techniques, regular staff update sessions are a useful way of keeping skills current. Patient education regarding motion management techniques, as well as selecting strategies on a case-by-case basis improve patient compliance. SP-0520 Prevetion of the radio-induced pulmonary fibrosis by Muse cells H. Dushime 1 , B. Petit 2 , J. Ollivier 2 , N. Gault 1 , M. Vozenin 2 , P. Romeo 1 1 cea, Drf/Jacob/Ircm/Lrts, Fontenay-Aux-Roses Cedex, France ; 2 chuv, Oncologie, Lausanne, Switzerland

Despite improved radiotherapy delivery conditions, radiation induced pulmonary fibrosis (RIPF) is a common complication in patients with lung or breast cancer after receiving thoracic radiotherapy. Radiation-induced injury in healthy tissues remain the limiting factor for dose escalation and tumor control. The average incidence of RIPF is 16-28% after radiotherapy(Cella et al. 2014). RIPF is characterized by progressive destruction of lung tissue and gas exchange disruption. To date no medical therapy has been approved for clinical use. Muse cells ("Multilineage differentiating stress enduring" cells) are a pluripotent mesenchymal stem cell (MSC) sub- population, easily isolated from bone marrow (BM-Muse) by cell sorting using an embryonic marker (SSEA3). When injected, these cells have the ability to migrate, integrate injured or inflammatory tissues and repair tissues through their immunomodulatory property and differentiation into tissue specific cells(Iseki et al. 2017; Kuroda et al. 2013). My project consists in the use of cell therapy using injection of Muse cells to reduce or prevent the development of RIPF. I use a well established mouse (C57BL/6J) model of RIPF(Sharplin et al. 1989; Jackso et al. 2010) to determine if intravenous injection of Muse cells (10 000- 60 000 BM-Muse) at 2h or 24h or 2 weeks after thoracic irradiation (14Gy X-Rad) reduce the development of fibrosis. Mice are followed during 20 weeks by Computed Tomography and survival. Then the animals are sacrificed and fibrosis is confirmed by histologic analysis of HES on lung sections. Our results showed that the 20-50% of irradiated non injected mice started to die 12 weeks irradiation and at 20 weeks the survival was 20-25%. In the group of mice treated with Muse (10 000- 30 000) 2h post RT, we observed survival of 100% of mice. CBCT and HES analysis showed that the 30 000 Muse cells prevent the development of fibrosis whereas 10 000 of Muse cells are not efficient to prevent the fibrosis but we observed a delay of RIPF development. In contrast when the mice were injected 24h or 2 weeks post RT, independent on the number of injected cells, we observed an improve of survival but all mice developed fibrosis.These experiments showed that Muse cells are able to prevent the development of RIPF without compromise the mice survival when injected early after irradiation. The perspective of this work is: To find new markers of Muse cells. To date, only the SSEA-3 marker discriminate the Muse cells from other MSC. A proteomic analysis is ongoing to find new markers characterizing Muse cells associated with their capacities of immunomodulation, differentiation and repair. This experiment will be performed on sorted Muse SSEA3 + and MSC negatives for SSEA3. To monitor in vivo the migration and localization of Muse cells soon after injection . The higher therapeutic potential of Muse cells compared to MSC is their integration at long term into the injured tissue wich seems to ease tissue reparation. Cells will be transfected with a luciferase plasmid that expressed luciferase with a high sensitivity and localization of muse cells in the lung will be monitored by bioluminescence in vivo . The precise localization of Muse cells will be confirmed by immunofluorescence on lung section using a specific anti-human HLA antibody. To investigate the role of Muse cells on inflammatory process and the modulation of immune response. After irradiation early tissue response include rapid production of pro-inflammatory cytokines (IL-3, IL-6, IL-7, TGFb, TNFa) promoting infiltration and activation of

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