Sci‐YIS Fri ‐ 07: Fitting the linear‐quadratic model to detailed data set for different dose ranges

Abstract

Survival curve behaviour and degree of correspondence between Linear Quadratic model1 (LQ) and experimental data in an extensive dose range for high dose rate was analyzed. Detailed clonogenic assays with irradiation given in 0.5Gy increments and a total dose range varying from 10.5 and 16Gy were performed. The cell lines investigated were: CHOAA8, hamster fibroblast cells; U373MG, human glioblastoma cells; and human prostate carcinoma cell lines CP‐3, and DU‐145. The analyses were based on χ2 statistic and Monte Carlo simulation of the experiment. A decline of fit quality at very low doses (<2Gy) is observed. This result can be explained by the hypersensitive effect observed in CHOAA8 and U373MG data and an adaptive type response in CP3 cell line. A clear improvement is discerned at slightly higher doses. This could be a result of the linearity existent in the trend of survival curve at low doses, that will affect the total fit in a range from 0Gy to final dose in linear quadratic region. The impact of including low dose data is shown through α/β ratios showing relative differences of 42, 40 and 23% for CHOAA8, CP3 and U373MG. LQ model cannot explain survival at high doses. This is shown as a deterioration of goodness of fit for high doses. A comparison of Linear Quadratic Linear model2 (LQL) with the LQ in fitting the experimental data at high doses was also performed.