ABSTRACT
This chapter provides an in-depth review of the application of the spheroid model system to specific areas of radiobiology. Toward this end, the diverse field of radiobiology has been divided into somewhat arbitrary, and certainly overlapping, thematic areas. The spheroid model would seem to be an ideal system for characterizing the development, cellular physiology, proliferative potential, and eventual fate of hypoxic cells. The concept that cell-cell contact can have a fundamental effect on the ability of a cell to survive therapeutic treatment represents an important contribution of spheroids to radiation biology. The fact that a minority of tumor cells show a contact effect for radiation may be related to their degree of differentiation or intercellular communication. The multicellular tumor spheroid system has made several contributions to our understanding of tumor radiobiology. The chapter concludes with an admittedly biased description of questions in radiobiology and radiotherapy to which spheroids could be applied in the future.
