Time Dose and Fractionation Effects

The linear-quadratic (LQ) model utilizes the terms α (single-hit kill) and β (two-hit kill) which correlate with low-dose killing and high-dose killing, respectively. Fractionation experiments with normal tissues (Chap. 23) for survival and functional tissue endpoints and tumor survival have allowed calculation of α/β ratios. These α/β ratios along with dose per fraction and total dose can be used to calculate biologically equivalent doses (BEDs) based on fraction size and total dose for various tissues and tumors compared to standard single fractions of no more than 2 Gy once a day, 5 days per week.