Modelling the cell survival using the RCR model : Bachelor Thesis in Medical Physics

• Main Author: Efimov, Grigory
• Format: Others
• Language: English
• Published: Stockholms universitet, Fysikum 2017
• Subjects: LET; hypoxia; RBE; OER; ion therapy; Physical Sciences; Fysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-150544

Background: Current studies in radiotherapy aim to develop better methods for curing patients fromcancer. Since different types of radiation interact with biological matter in various ways, the resultsof their interaction and their effectiveness with respect to the biological damage to cells have ageneral investigation interest. Aim: The work in this project aims to use a mathematical model to fit a pre-existing data onclonogenic survival of cells irradiated by different types of radiation and report the fittingparameters. Various radiobiological concepts were investigated and compared between differentradiation qualities used in this work. Materials and Methods: The repairable-conditionally repairable (RCR) damage model parametrisedwith respect to the linear energy transfer (LET) of the cell oxygenation was used for fittingexperimental cell survival data for human salivary gland cells irradiated in oxic and hypoxicconditions with protons, 12C-, 20Ne- and 3He-ions. Results: Good consistency with the entire cell survival data was achieved. RCR-model was robustenough to achieve agreement with cell survival data for LET values excluded from fitting procedure.Slope of cell survival curves for the three ions increased up to optimal LET value reaching maximumthere and it decreased at higher LETs. RBE of 3He-ions showed the most rapid increase in low-LETregion and reached a higher maximum as compared with other ions. RBE of the three ions increasedapproximately in the same LET region as a and c parameters of RCR-model, but no underlyingradiobiological mechanism could explain any of curve shape similarities. The RBE of 12C-ions reachedmaximum approximately at 126 keV/μm, which is the optimal LET that could possibly correspond tothe steepest cell survival curve. It was observed how the cell oxygenation became less important forcell irradiation with very high LET values. Conclusion: The results showed that it is feasible to use the RCR model to fit the broad range of cellsurvival curves corresponding to different radiation qualities and the assessment of their relativebiological effectiveness in oxic and hypoxic irradiation conditions. RCR-model may have a possible application in cell irradiation with other ion beams than those used in this work.