Implications of tumor cell kinetics in radiotherapy and radiobiology

Data in cellular kinetics of human solid tumors over past 20 years were evaluated with the reference to the radio-responsiveness or radiocurability in various histological types. The geometric mean of thymidine labeling index (LI) and volume doubling time (TD) vary significantly among 10 histological types. The regression analysis between LI and parameters of cellular kinetics indicated that growth fraction (GF) correlated best with the corresponding LI not only among tumors of various histological types, but also among individual tumors in a same type. Further, a significant correlation has been also reported between TD or LI, and the radiation response or prognosis. Although mechanism involved in the correlations is presently difficult to understand, the difference between P and Q cells seems important in the aspect of the hypoxic cell fraction, clonogenicity and radiosensitivity in both cell populations. (author)