[Hypoxic cell radiosensitizer present status and problems from viewpoint of clinical radiotherapy]

The results of clinical trials of hypoxic cell radiosensitizers were reviewed in order to clarify the present status and problems in this field. Most trials failed to show an effectiveness of the combination, however, some ENT tumors and bladder cancers were improved in local tumor responses and survivals. A selection of the patients suitable for the combination and development of simple method for the selection are indispensable. SERs necessary for clinical radiotherapy are considered to be larger than 1.2 at 2 Gy fraction level. Present hypoxic cell radiosensitizers have no significant effects on alpha values. Since radiation responses at low radiation dose ranges are dominated by alpha values, the chemicals having an effects on alpha values have to be developed.