Oxygen, oxygen plus carbon dioxide, and radiation therapy of a mouse mammary carcinoma

Abstract

A series of radiation‐dose tumor control response assays have been performed using an 8‐mm diameter C3H mouse mammary carcinoma, and radiation administered in 10 equal doses with 24‐hour intervals between treatments. The studies evaluated the effectiveness of administering the radiation while the mice respired oxygen at normal pressure for 5, 15, or 60 min., or respired 95% O2 and 5% CO2 at normal pressure for 30 sec. or 15 min. prior to each local irradiation, or respired oxygen at 30 psi after 5 or 15 min. prior to each irradiation. The TCD50 values for these assays showed that there was no advantage to use of O2 and CO2 instead of pure oxygen at normal pressure in the fractionated irradiation of this particular tumor. There was a marked increase in effectiveness of treatment for animals respiring oxygen at normal pressure instead of air, and the effectiveness increased as the exposure to oxygen was lengthened from 0 to 5 to 15 min. However, local irradiation was less effective if administered to mice which had respired oxygen for 60 min. prior to each treatment session. By far, the most effective treatment method for this particular tumor was for the mice to respire oxygen at 30 lb. per square min. for 5 min. or 15 min. Interestingly, there was no advantage in allowing the mice to respire the oxygen at the high pressure for 15 min. instead of 5 min., i.e., the TCD50 was the same for the two times of respiration of oxygen. Copyright © 1972 American Cancer Society