Comparison of Hyperbaric Oxygen and Misonidazole in Fractionated Irradiation of Murine Tumors

The enhancement ratios for hyperbaric oxygen (${\rm O}_{2}3{\rm ATA}$) and for misonidazole (0.3 mg/g body wt) for fractionated irradiation (5 or 10 equal doses) of two spontaneous tumors and of normal skin of the C3H mouse have been determined. The two tumors were a C3H mouse mammary carcinoma and a squamous cell carcinoma; they were used as third-generation isotransplants and were 8 and 6 mm in diameter, respectively, and grew in the right leg. Acute skin reactions were scored for mice irradiated 18 days after plucking hair from the leg. Enhancement ratios for the ${\rm TCD}_{50}$ values were virtually the same for ${\rm O}_{2}3{\rm ATA}$ and misonidazole, 1.45-1.55. For acute skin reaction the enhancement ratio was higher for ${\rm O}_{2}3{\rm ATA}$, i.e., 1.94 vs 1.54 for misonidazole.