Changes in tumor oxygenation during a combined treatment with fractionated irradiation and hyperthermia: an experimental study.
OBJECTIVE
To determine the influence of adjuvant hyperthermia on the oxygenation status of fractionated irradiated tumors.


METHODS
Oxygen partial pressure (pO2) in rat rhabdomyosarcomas (R1H) was measured sequentially at weekly intervals during a fractionated irradiation with 60Co-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 pO2 measurements (pO2-histograph, Eppendorf, Germany) were performed in anesthetized animals during mechanical ventilation and in hemodynamic steady state. All tumor pO2 measurements were correlated to measurements of the arterial oxygen partial pressure (paO2) determined by a blood gas analyzer.


RESULTS
The oxygenation status of R1H tumors decreased continuously from the start of the combined treatment, with increasing radiation dose and number of heat fractions. In untreated controls a median tumor pO2 of 23 +/- 2 mmHg (mean +/- SEM) was measured. Tumor pO2 decreased 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 pO2-values below 5 mmHg and the decrease in the range of the pO2 histograms [delta p(10/90)] further indicated that tumor hypoxia increased relatively rapidly from the start of combined treatment. After 60 Gy + 8HT 48 +/- 5% (mean +/- SEM) of the pO2-values recorded were below 5 mmHg.


CONCLUSIONS
These findings suggest that adjuvant hyperthermia to radiotherapy induces greater changes in tumor oxygenation than radiation alone [cf. (39)]. This might be of importance for the temporary application of hyperthermia in the course of a conventional radiation treatment.
Zywietz
F
F
Institute of Biophysics and Radiobiology, University Hospital Eppendorf, Hamburg, Germany.
Reeker
W
W
Kochs
E
E
D000818:Animals; D003131:Combined Modality Therapy; D006979:Hyperthermia, Induced; D008297:Male; D009368:Neoplasm Transplantation; D009369:Neoplasms / Q000098:blood supply / Q000378:metabolism* / Q000532:radiotherapy / Q000628:therapy*; D010100:Oxygen / Q000378:metabolism*; D010313:Partial Pressure; D011879:Radiotherapy Dosage; D051381:Rats; D012208:Rhabdomyosarcoma / Q000098:blood supply / Q000378:metabolism / Q000532:radiotherapy / Q000628:therapy
D010100:Oxygen