This study has attempted to address the controversy concerning sustained increases in
tumor oxygenation upon localized mild
hyperthermia. While some previous studies have reported transient increases, others have reported persistent increases in
tumor oxygenation, lasting for upto 2 days after application of mild
hyperthermia. In order to determine changes in oxygenation at clinically relevant
tumor temperatures, experimental
tumors in rats underwent localized
hyperthermia at either 40, 41.8 degrees C or 43 degrees C for 1 h using water-filtered infrared-A irradiation. Oxygenation was continuously measured before, during and upto 60 min after
hyperthermia in the
tumors of anesthetized rats using
oxygen-sensitive
catheters. The data obtained indicate that localized
hyperthermia can lead, on average to an improved
tumor oxygenation, although this improvement is generally transient and no longer evident 1 h after heating. Since clinically relevant increases in oxygenation enduring beyond the heating period were rarely seen, it would appear that an improvement in the efficacy of
oxygen-dependent
cancer therapy is unlikely to be achieved in the post-
hyperthermia period.