Changes in tumor oxygenation during a combined treatment with fractionated irradiation and hyperthermia: an experimental study

Int J Radiat Oncol Biol Phys. 1997 Jan 1;37(1):155-62. doi: 10.1016/s0360-3016(96)00465-8.


Purpose: To determine the influence of adjuvant hyperthermia on the oxygenation status of fractionated irradiated tumors.

Methods and materials: 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.

MeSH terms

  • Animals
  • Combined Modality Therapy
  • Hyperthermia, Induced*
  • Male
  • Neoplasm Transplantation
  • Neoplasms / blood supply
  • Neoplasms / metabolism*
  • Neoplasms / radiotherapy
  • Neoplasms / therapy*
  • Oxygen / metabolism*
  • Partial Pressure
  • Radiotherapy Dosage
  • Rats
  • Rhabdomyosarcoma / blood supply
  • Rhabdomyosarcoma / metabolism
  • Rhabdomyosarcoma / radiotherapy
  • Rhabdomyosarcoma / therapy


  • Oxygen