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Effects of Uncertainties of Radiation Sensitivity of Biological Modelling for Treatment Planning

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M Oita

M Oita1,2*, Y Uto2, M Tominaga3, M Sasaki4, H Hori2 (1) Department of Radiological Technology, Graduate School of Health Sciences, Okayama University (2) Department of Life System, Institute of Technology and Science, Graduate School,The Tokushima University (3) Department of Radiological Technology, Institute of Health Biosciences, Graduate School, The Tokushima University (4) Department of Radiology, Tokushima University Hospital


SU-E-T-146 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:The aim of this study was to evaluate the distribution of uncertainty of cell survival by radiation, and assesses the usefulness of stochastic biological model applying for gaussian distribution.

Methods:For single cell experiments, exponentially growing cells were harvested from the standard cell culture dishes by trypsinization, and suspended in test tubes containing 1 ml of MEM(2x10⁶ cells/ml).
The hypoxic cultures were treated with 95% Nâ‚‚-5% COâ‚‚ gas for 30 minutes. In vitro radiosensitization was also measured in EMT6/KU single cells to add radiosensitizer under hypoxic conditions. X-ray irradiation was carried out by using an Xray unit (Hitachi X-ray unit, model MBR-1505R3) with 0.5 mm Al/1.0 mm Cu filter, 150 kV, 4 Gy/min). In vitro assay, cells on the dish were irradiated with 1 Gy to 24 Gy, respectively. After irradiation, colony formation assays were performed. Variations of biological parameters were investigated at standard cell culture(n=16), hypoxic cell culture(n=45) and hypoxic cell culture(n=21) with radiosensitizers, respectively. The data were obtained by separate schedule to take account for the variation of radiation sensitivity of cell cycle.

Results: At standard cell culture, hypoxic cell culture and hypoxic cell culture with radiosensitizers, median and standard deviation of alpha/beta ratio were 37.1±73.4 Gy, 9.8±23.7 Gy, 20.7±21.9 Gy, respectively. Average and standard deviation of D₅₀ were 2.5±2.5 Gy, 6.1±2.2 Gy, 3.6±1.3 Gy, respectively.

Conclusion: In this study, we have challenged to apply these uncertainties of parameters for the biological model. The variation of alpha values, beta values, Dâ‚…â‚€ as well as cell culture might have highly affected by probability of cell death. Further research is in progress for precise prediction of the cell death as well as tumor control probability for treatment planning.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Grant-in-Aid for Young Scientists (B) No. 25861105 from MEXT Japan.

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