CHANGES IN TUMOR OXYGENATION DURING A COMBINED TREATMENT WITH FRACTIONATED-IRRADIATION AND HYPERTHERMIA - AN EXPERIMENTAL-STUDY

Purpose: To determine the influence of adjuvant hyperthermia on the ox ygenation status of fractionated irradiated tumors. Methods and Materi als: Oxygen partial pressure (pO(2)) in rat rhabdomyosarcomas (R1H) wa s measured sequentially at weekly intervals during a fractionated irra diation with Co-60-gamma-rays (60 Gy/20f/4 weeks) in combination with local hyperthermia (8 f(HT) at 43 degrees C, 1 h/4 weeks), Tumors were heated twice weekly with a 2450 MHz microwave device at 43 degrees C, 1 h starting 10 min after irradiation, The pO(2) measurements (pO(2)- histograph, Eppendorf, Germany) were performed in anesthetized animals during mechanical ventilation and in hemodynamic steady state, All tu mor pO(2) measurements were correlated to measurements of the arterial oxygen partial pressure (paO(2)) determined by a blood gas analyzer. Results: The oxygenation status of R1H tumors decreased continuously f rom the start of the combined treatment, with increasing radiation dos e and number of heat fractions. In untreated controls a median tumor p O(2) of 23 +/- 2 mmHg (mean +/- SEM) was measured, Tumor pO(2) decreas ed to 11 +/- 2 mmHg after 30 Gy + 4 HT (2 weeks), and to 6 +/- 2 mmHg after 60 Gy + 8HT (4 weeks), The increase in the frequency of pO(2)-va lues below 5 mmHg and the decrease in the range of the pO(2) histogram s [Delta p(10/90)] further indicated that tumor hypoxia increased rela tively rapidly from the start of combined treatment, After 60 Gy + 8HT 48 +/- 5% (mean +/- SEM) of the pO(2)-values recorded were below 5 mm Hg. Conclusions: These findings suggest that adjuvant hyperthermia to radiotherapy induces greater changes in tumor oxygenation than radiati on alone [cf, (39)], This might be of importance for the temporary app lication of hyperthermia in the course of a conventional radiation tre atment. Copyright (C) 1997 Elsevier Science Inc.