APPLICABILITY OF LINEAR QUADRATIC AND MULTI-TARGET MODEL TO SINGLE AND FRACTIONATED RADIOTHERAPY IRRADIATION
The effect of fractionation in radiotherapy had been experimentally proven to increase the surviving fraction of the cells instead of single irradiation. Cell survival described by radiobiological models could be used to predict the radiosensitivity and sublethal damage repair of cells to radiation. In this study, the linear quadratic (LQ) and multi-target (MT) cell survival curve models were used to describe the cell survival curves with single and fractionated irradiation. HeLa cells were irradiated using 6 MV photon beam with 10×10 cm2 field size, 100 cm SSD at different doses. Standard clonogenic assay was performed to determine cell survival. The experimental data were fitted to the LQ and MT model using OriginPro 9.2 software. Radiobiological parameters were evaluated from the fitting curves generated from these models. Results show that the survival curves fitted with LQ and MT model for single irradiation displayed steep initial slope and small shoulder. The sublethal damage repair was better for fractionated irradiation with a wider shoulder. The parameters of LQ model showed a larger α and α/β ratio whereas for MT model showed a smaller n, Do and Dq. Analysis of the LQ and MT model parameter shows that single irradiation induced more cell death. MT model seems to be more accurate in describing the radiosensitivity of the cells especially at a high dose for both single and fractionated irradiations. The most commonly used model, LQ seems to provide unsatisfactory fitting at a high dose.