 2. Reduction of radiosensitivity Unfortunately, how radiosensitizing drugs can modify radiosensitivity cannot be evaluated retrospectively. Actually, the efficacy is evaluated on the basis of an overall effect of the treatment but radiosensitivity changes day by day in radiation and pharmacological concurrent treatment. However, these changing in radiosensitivity can be analysed in pre-clinical setting. In many reports, a progressively higher radiosensitivity has been shown in cellular survival curves by increasing EGFR inhibitor concentration. Nevertheless, the concentrations of EGFR inhibitor do not correspond to in vivo concentration during radiotherapy delivery. Fortunately, this data is obtainable from Cetuximab pharmacokinetic curve. Therefore, cell survival curves corresponding to drug concentration were obtained by performing a graphic interpolation. From these curves, daily radiosensitivity parameters were found. 