Hypoxic cells in reoxygenation: Role of radiation resistance

Results from experiments on murine tumors performed by a variety of investigators have demonstrated that (1) there are hypoxic and viable cells present and (2) respiration of oxygen at increased pressure or administration of chemical sensitizer of hypoxic cells (i.e., metronidazole or misonidazole) in combination with fractionated irradiation achieved significant reduction in the TCD50 values. In review of the studies of human tumors, emphasis was placed on examination for evidence that the maneuvers which overcome, to an important extent, the impact of hypoxic cells in murine tumors succeed when applied clinically. This is true because at present we cannot directly determine the role of hypoxic cells in the failures of conventional radiation therapy. Data from clinical trials are not entirely consistent but do indicate that for some human tumors local results are improved by combining radiation with hyperbaric oxygen or chemical sensitizers. These tumors include carcinomas of the head and neck, bronchus and high-grade gliomas. The results for hyperbaric oxygen and radiation in the treatment of carcinoma of the uterine cervix are mixed and must be classed as only suggestive. For carcinomas of the urinary bladder (hyperbaric oxygen and radiation) and for osteosarcoma (radiation under tourniquet conditions) the available results are equivocal