ESTRO 36 Abstract Book

S10 ESTRO 36 _______________________________________________________________________________________________

Material and Methods We used two non-transformed human lung fibroblasts, MRC5 and IMR 90 and one human lung cancer cell line, A549. Cells were grown on coverslips and given 5 Gy with the same LINAC (4.5 MeV electrons) in the FLASH or CONV mode 24 h after seeding. EBT3 Gafchromic films were used to assess the dose received by each flask. Cell viability was evaluated 6 days post-irradiation (pi) by a MTT assay for the three cell lines and manual cell counting for the two fibroblastic cell lines. A clonogenic survival assay was also performed for A549 cells. For DNA damage response studies, γH2AX and 53BP1 foci were detected by an immunofluorescence method. To quantify those foci, z- stack images across the nucleus were acquired on a SP5 Leica confocal microscope and foci analyzed using the 3D object counter software. The data came from 2 - 4 experiments performed under the same conditions and analysed with the same modalities. The statistical tests were Wilcoxon (cell viability) and Student (DNA damage response). Results The MTT assay did not show any difference between CONV vs. FLASH modalities. For A549 cells, the median of the MTT signal was 86.6% after CONV vs. 78.8% after FLASH (p=0.7); for MRC5, 61.3% (CONV) vs. 57% (FLASH, p=0.4); and for IMR 90, 72.7% (CONV) vs. 72.5% (FLASH, p=1). Cell counting did not find any difference too: for MRC5 cells, the median of the % of live cells was 20% (CONV) vs. 15.9% (FLASH, p=0.1); for IMR 90, 15.8% (CONV) vs. 15.1% (FLASH, p=0.3). The clonogenic survival assay did not show any difference for A549 after CONV vs. FLASH. For DNA damage study, the mean number of γH2AX and 53BP1 foci was determined for the three cell lines, at 30 and 180 min pi. No statistically significant difference was observed between the two modalities of irradiation. For A549 cells, the mean number of γH2AX foci, 30 min pi, was 30 ± 9 after CONV vs. 29 ± 10 after FLASH (p=0.6); for MRC5, 31 ± 10 for the two modalities of irradiation; and for IMR 90, 37 ± 11 after CONV vs. 39 ± 15 after FLASH (p=0.36).

Conclusion This in vitro study did not elicit any significant difference, between CONV and FLASH, in both tumoral and non- tumoral cell lines with cell viability and foci of DNA damage repair proteins as endpoints. This suggests that the differences evidenced from in vivo studies result from the microenvironment and/or immune responses. OC-0031 Global changes in the glycosylation of irradiated endothelial cells with functional consequences C. Jaillet 1 , W. Morelle 2 , M.C. Slomianny 2 , V. Paget 1 , G. Tarlet 1 , V. Buard 1 , S. Selbonne 1 , F. Caffin 1 , E. Rannou 1 , P. Martinez 2 , A. François 1 , F. Foulquier 2 , F. Allain 2 , F. Milliat 1 , O. Guipaud 1 1 Institute for Radiological Protection and Nuclear Safety, Purpose or Objective Altered by ionizing radiation, the vascular network is considered as a prime target to limit normal tissue damages and improve tumor control in the context of radiotherapy. Irradiation activates endothelial cells which then participate in the recruitment of circulating cells, especially by overexpressing cell adhesion molecules but also by other yet unknown mechanisms. In this study, we aimed to determine whether irradiation modifies the endothelium glycosylation pattern and to investigate the impact of these changes on the adhesion of circulating cells. PRP-HOM, Fontenay aux Roses, France 2 University of Lille, UGSF, Lille, France