CORRELATION BETWEEN RADIOSENSITIVITY, PERCENTAGE HYPOXIC CELLS AND PO(2) MEASUREMENTS IN ONE RODENT AND 2 HUMAN TUMOR XENOGRAFTS

Computerized pO(2) histography has been used to measure the intratumor pO(2) in patients for the past few years, and there is now evidence t hat these tumors contain hypoxic cells. One of the major questions tha t remains to be answered is the relevance of such data to radiosensiti vity. The present study looks for a correlation between intratumor pO( 2), the percentage of hypoxic cells in the tumor and the radiosensitiz ation induced by carbogen and/or the oxygen carrier, perflubron emulsi on. Two human tumor xenografts (HRT18, Na11+) and one rodent tumor (EM T6) were used. The radiosensitivity (clonogenic assay) and the oxygen tension (computerized pO(2) histography) were measured. All experiment s were performed under similar conditions. Carbogen increased tumor ra diosensitivity; sensitization was greatest when 4 ml/kg perflubron emu lsion was used in conjunction with carbogen. The pO(2) distribution wa s shifted to higher pO(2) values in the tumors whatever the treatment; the shift was greater for perflubron emulsion plus carbogen. The low pO(2) values (<0.4 kPa) were lost for the HRT18 cells. A correlation ( EMT6, HRT18) or a link (Na11+) between the radiosensitization and the oxygen tension measurements was found for values below 1.07 or 1.33 kP a. A trend between the percentage of hypoxic cells and pO(2) measureme nts was found taking into account pO(2) measurements comprised between 0.27 and 0.67 kPa.