ESTRO 2021 Abstract Book

S291

ESTRO 2021

Results Twenty-five patients were included in the study of which 20 could be analyzed. Lung tumor slices remained vital ex vivo and contained proliferating tumor cells even after 7 days of culture. The uptake in the slices (n=77) in the PET images ranged from 1.9% to 140.1% (average 26% + 29%) (compared to 1.7% for the slices treated with cisplatin) and correlated well with the uptake from the gamma counter measurements (Pearson correlation > 0.97, 26 slices). The relation between FDG uptake and number of proliferating tumor cells differed per patient (p<0.0036). The observed variation in FDG uptake could not be explained by the variation in proliferating cells (p=0.31) (Figure 2).

Conclusion We showed that lung tumor tissue slices can be kept viable ex vivo for seven days, that FDG can be administered ex vivo and effectively washed off, and that FDG uptake by the slices can be imaged accurately using a micro PET scanner. The method presents a novel, cheap and accessible first step to study the potential of novel PET tracers for response based dose-painting. As proof of principle, the method was applied to FDG, which showed no correlation with the proliferation marker Ki-67, as surrogate for cell vitality. OC-0396 Decrease in tumour blood flow during radiation predicts overall survival in rectal cancer K. Bakke 1 , S. Meltzer 1 , E. Grøvik 2 , A. Negård 3 , S.H. Holmedal 3 , L.T.G. Mikalsen 2 , L.G. Lyckander 4 , F.M.I. Julbø 1 , A. Bjørnerud 5 , K. Gjesdal 6 , A.H. Ree 7 , K.R. Redalen 8 1 Akershus University Hospital, Department of Oncology, Lørenskog, Norway; 2 Oslo University Hospital, Department of Diagnostic Physics, Division of Radiology and Nuclear Medicine, Oslo, Norway; 3 Akershus