Growth kinetic aspects of the radiobiology of human malignant tumors grown in nude mice

This study has shown that the nude mouse model is well suited for in vivo investigations of the growth kinetics of human malignant tumors. The model enables the study of the effect of irradiation on human tumors, and the methods applied are appropriate for a differentiated description of kinetic aspects of the radiobiology as they provide complementary results. The growth curve studies showed that the Gompertz function was well suited to describe the macroscopic growth of heterotransplanted human malignant tumours. The applied transformation of the growth function was appropriate for the calculation of the radiation-induced growth delay, which was the only reliable growth curve parameter for the assessment of the treatment effect. The flow cytrometric DNA analysis was an appropriate method in checking the stability of tumors during serial transplantation, and the analysis is well suited for identification of tumor populations, e.g., in the comparison of tumors in nude mice with the original patient tumors. Determination of the DNA index in the colonic carcinoma revealed a change of ploidy due to a clonal evolutionary process, which was indetectable by histological and growth curve examination, and which affected the radiosensitivity of the tumor. The sequential determination of the cell cycle distribution of irradiated tumors provided rapid information on cellular synchronization and on redistribution time. These data may be applicable in the design of fractionated irradiation. (EG)