ESTRO 37 Abstract book

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ESTRO 37

Promega CellTiter 96 ® AQueous One) and double-strand DNA breaks (γ-H2AX, In-Cell Western® assay, LI-COR Biotechnology) were measured and compared. In addition, melanoma cells were irradiated to 18 Gy using 10 MV and 2400 MU/min X-rays either continuously (cont) or with 3 minute breaks (break_3) or 10 minute breaks (break_10) after delivering each 3 Gy. Cell viability and double-strand DNA breaks were measured and compared. Graphpad Prism was used to generate graphs and for data analysis. Results For melanoma cells, mean cell viability with 400 MU/min radiation dose-rate for 15, 18 and 24 Gy were 0.66, 0.65, 0.65, and with 2400 MU/min they were 0.65, 0.63, 0.69. For glioma cells, the corresponding values were 0.24, 0.22, 0.22 and 0.23, 0.22, 0.23. These differences were not statistically significant, p = .92 for melanoma and p = .87 for glioma cells ( Figure 1, A & B ). There were no significant differences in double-strand DNA breaks in melanoma cells as measured by the relative γ-H2AX signal intensities with mean values of 99.7, 120, 162.9 for 15, 18 and 24 Gy for 400 MU/min and 118.7, 102, 165.4 for 2400 MU/min dose-rate irradiations (p = .98; Figure 1, C & D ).

fraction breaks for typical radiation dose ranges used for clinical treatments with SRT. Further validation of our results with in-vivo models is required. However, we do not find significant evidence for radiobiological differences, atleast in terms of dose rate and intra- fraction breaks, between platforms such as robotic-, isotope-, and high dose rate linac-based SRT. EP-2312 Biological validation of a high-throughput in- vitro radiobiology platform K. Thippu Jayaprakash 1,2 , D. Mostafa 3 , M. Hussein 3 , A. Nisbet 3,4 , R. Shaffer 2 , M. Ajaz 1,2 1 University of Surrey, Department of Clinical and Experimental Medicine, Guildford, United Kingdom 2 St Luke's Cancer Centre- Royal Surrey County Hospital, Department of Oncology, Guildford, United Kingdom 3 St Luke's Cancer Centre- Royal Surrey County Hospital, Department of Medical Physics, Guildford, United Kingdom 4 University of Surrey, Department of Physics, Guildford, United Kingdom Purpose or Objective Pre-clinical in-vitro radiobiology platforms lack efficiency for conducting radiobiology experiments. We have developed and dosimetrically validated a high-throughput in-vitro radiobiology platform utilising an advanced clinical radiation technique, Intensity Modulated Radiotherapy (IMRT) to deliver multiple radiation doses to tissue culture plates in the same plan 1 . Here we report biological validation of this radiobiology platform. Material and Methods Melanoma (A375) and glioma (LN18) cells in 96- and 6- well tissue culture plates were placed in a custom made perspex tissue culture plate holder, and were irradiated in a linear accelerator with dosimetrically verified 96- and 6-well tissue culture plate IMRT plans to target radiation doses of 0, 2, 4, 8, 16 and 24 Gy. Cells were also irradiated with conventional open-field, homogeneous irradiations to the same nominal doses. Cell viability (tetrazolium colorimetric cell viability (MTS) assay, Promega CellTiter 96 ® Aqueous One), cell proliferation (clonogenic assay) and double-strand DNA breaks (quantitative γ-H2AX analysis, In-Cell Western ® assay, LI-COR Biotechnology) of plate IMRT plans were compared to those delivered by open-field irradiations. GraphPad Prism was used to generate graphs and for statistical analysis. Results For A375 cells, cell viability for 0, 2, 4, 8, 16 and 24 Gy for the 96-well IMRT plan were 2.08, 1.75, 1.42, 0.76, 0.55, 0.55, and with open-field, homogeneous irradiations they were 2.08, 1.65, 1.18, 0.65, 0.52, 0.5. These differences were not statistically significant (p = .82, unpaired t-test) ( Figure 1, a ). The corresponding values for LN18 cells were 2.01, 1.7, 1.39, 0.77, 0.27, 0.25 and 1.91, 1.65, 1.33, 0.66, 0.35, 0.37 respectively, and again these differences did not reach statistical significance (p = .95, unpaired t-test) ( Figure 1, b ).

When 18 Gy was delivered with a continuous irradiation plan (cont), mean cell viability for melanoma cells was 0.46 and with intra-fraction breaks, it was 0.46 for break_3 and 0.49 for break_10, these differences were not statistically significant (p = .93 ; Figure 2, A) . No significant differences in double-strand DNA breaks were observed with relative γ-H2AX signal intensities of 107.2, 142.4 and 130.6 for irradiation plans cont, break_3 and break_10 respectively (p = .12 ; Figure 2, B & C) .

Conclusion No significant differences in biological effects were observed with different radiation dose-rates and intra-