Heating of a rhabdomyosarcoma of the rat by 2450 MHz microwaves: technical aspects and temperature distributions

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 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.

Experimental thermoradiotherapy of human tumour xenografts in nude mice; design of the hyperthermia system

An experimental thermoradiotherapy study was started in 1986. For this study a hyperthermia system was developed for heating human tumours xenotransplanted into nude mice. The treatment device was a four-channel computer-controlled hyperthermia system. Temperature was monitored by microwave radiometry at 3 GHz. Specifications of the radiometer were evaluated first under reference conditions. Subsequently, thermal dosimetry was studied using non-invasive measurement of brightness temperature, TOR. Hyperthermia treatments were simulated in phantom material with radiometric monitor values, TR, of 40 and 41. In conjunction with the parameters of TOR, surface temperature, T0, and water bolus temperature, TW, thermal modelling was performed. Influence of a perfused phantom also was studied on microwave thermometry.

Experimental thermoradiotherapy of human tumour xenografts in nude mice: design of the hyperthermia system

An experimental thermoradiotherapy study was started in 1986. For this study a hyperthermia system was developed for the heating of human tumours xenotransplanted into nude mice. Our treatment device was a four-channel computer-controlled hyperthermia system. Temperature was monitored by microwave radiometry at 3 GHz. Specifications of the radiometer were first evaluated under reference conditions, then thermal dosimetry was studied using non-invasive measurement of the brightness temperature TOR. Hyperthermia treatments were simulated in phantom material with radiometric monitor values TR of 40 and 41. In conjunction with the parameters of brightness temperature TOR, surface temperature TO and water bolus temperature TW thermal modelling was performed. Finally, we studied the influence of a perfused phantom to the microwave thermometry.