The effect of irradiation of the oxygen removal rate of the SSBIa rat fibrosarcoma

Direct measurement of reoxygenation in malignant mammary tumors after a single large dose of irradiation

Measurements of the tissue O2 partial pressure distribution in C3H mouse mammary adenocarcinomas were performed just before and 72 - 74 hrs. after X- irradiation using O2 microelectrodes of the gold in glass type. The results obtained before irradiation were similar to those usually obtained previously in fast growing murine tumors during advanced growth stages. After exposure to a single dose of 60 Gy, the distribution curve significantly changed. This change was particularly evident in the very low pO2 range which is of crucial importance for the efficacy of radiotherapy. Due to this improvement of the tumor tissue oxygenation the number of radioresistant cells can be drastically reduced in the post- irradiation period at the time of maximum reoxygenation. Judiciously chosen fractionated treatment regimens, thus, should maintain tumor cells in optimum radiosensitivity states.

The diffusion coefficient of oxygen in respiring kidney and tumour tissue

The diffusion coefficient and permeability, together with the oxygen uptake rate, have been measured in slices of respiring tissue. Values of these quantities are given for mouse kidney cortex and for implanted tumours of Lewis lung carcinoma in the mouse, and the fibrosarcoma SSB1a in the rat. The diffusion coefficient at 22 degrees C is 1.3 . 10(-5) . cm2 . s(-1) in the kidney, and has the higher value of 1.6 . 10(-5) . cm2 . s(-1) in both tumours. The solubility in all three tissues is similar to that in saline.

Comparison between the oxygen removal rate and the histological structure of normal and tumour tissues

A technique has been used to measure distributions of oxygen removal rate, QR, in samples of recently excised tissue where QR is defined as the ratio of the oxygen uptake rate to the oxygen solubility. QR was measured at 91 sampling points across a cross section of tissue of diameter 5 mm. By placing markers in the tissue and using special procedures to obtain sections of the tissue samples it was possible to compare the distributions of QR with the histological structure of the tissues. The overall resolution of the system is about 1/2 mm so that structures of the order of a millimetre or more could be examined. There are considerable inhomogeneities in QR within some normal tissues, for example 4-19 mm Hg/s in rat kidney and 0.4-1.5 mm Hg/s in human cervix. Inhomogeneities in tumour tissues are also associated with the histological structure and examples for the Lewis lung mouse carcinoma show a correlation between QR and regions of viable or necrotic tissue. For a biopsy sample of human carcinoma of the cervix QR correlates with the degree of local infiltration by tumour cells.