Influence of ultrasound-induced hyperthermia and X-irradiation on the incidence of metastases from a solid tumor.

The KHT sarcoma transplanted into mouse legs was treated by X-irradiation, hyperthermia or a combination of X-irradiation plus hyperthermia. Neither 20 Gy of X-irradiation or hyperthermia for 60 min were effective in controlling the local tumors when used alone. Simultaneous treatments, however, resulted in 22% of the tumors being locally controlled corresponding to a TER of 2.0. Local control was increased when irradiation was given 1 h before or after hyperthermia, TER 2.8 and was maximum, TER 2.9, when the hyperthermia was 0.1 h after irradiation. When the local tumor was controlled by irradiation alone or by irradiation delivered 1 h before or after hyperthermia, all of the metastases that subsequently occurred arose before or during treatment. When tumors were locally controlled by radiation given during or immediately after hyperthermia, metastases developed that must have occurred as a consequence of the treatment. The treatment sequence that resulted in a maximum TER for tumor control did not correlate with the risk of metastatic spread. The timing of the irradiation in relation to hyperthermia may explain some contradictory findings regarding the influence of heat on the incidence of metastases. Hyperthermia did not affect the distribution of anatomic sites involved with metastases or the ratio of lymphatic to hematogenously spread metastases.