Abstract
Tumor size, which is readily measurable in clinical situations, is one of the most important predictors of radiation response for tumors of a specified histological type. We propose in this paper a simple model that defines the tumor radioresistance in terms of tumor control dose (TCD) relative to tumor volume, assuming that the number of target cells is proportional to the power function of tumor volume. In the model the TCD increases linearly with increasing logarithm of tumor volume, with a slope proportional to the effective Do of the target cells. The model was applied to the analysis of radioresistance of 169 cervical lymph node-metastases from head and neck cancers. Unsing the logistic multivariate regression equation, the TCD was expressed as a function of tumor volume. Result indicated that the lymph node-metastases become progeressively radioresistant with increasing tumor volume. This was strongly suggested to be caused by progressive increase in the radioresistance of the target cells.
