PRETREATMENT OXYGENATION PROFILES OF HUMAN SOFT-TISSUE SARCOMAS

Purpose: Tumor oxygenation is thought to influence the radiocurability of many malignancies. Advances in polarographic electrode technology have facilitated the in situ measurement of human tumor pO(2). The opt imal method of defining a ''hypoxic'' tumor is not known. Characteriza tion of intra-tumor and intertumor pO(2) heterogeneity could help with this process. This study was performed to evaluate pretreatment tumor oxygenation status and pO(2) heterogeneity in patients with soft tiss ue sarcoma. Methods and Materials: Nine patients with soft tissue sarc omas underwent pretreatment pO(2) measurements with the Eppendorf pO(2 ) histograph. Two grossly distinct anatomic sites within each tumor we re measured in all but one patient; these were localized under compute rized tomography guidance to ensure that all measurements were obtaine d from tumor tissue. Multiple probe tracks were studied at each site. Measurements were performed in resting, awake patients. Results: A tot al of 1588 pO(2) readings was obtained (mean = 176/patient). Measureme nt path lengths ranged from 22-36 mm. The average hypoxic fraction (pO (2) < 5 mm Hg) was 29% (range 0-76%). Arterial pO(2) was positively co rrelated with mean and median tumor pO(2). Tumor hypoxic fraction incr eased with increasing tumor volume. Linear pO(2) profiles and frequenc y histograms provided similar estimates of the extent of hypoxia in in dividual tumors. Marked variation in oxygenation existed both within a nd between individual tumors. The intertumor variation was greater tha n the intratumor variation. Conclusion: Radiobiologic hypoxia exists i n human soft tissue sarcomas. The pO(2) variation within individual tu mors is less than the variation between tumors. Further study is neces sary to identify the best parameter for defining tumor hypoxia and to discern the relationship between tumor pO(2) and treatment outcome.