During the past few years hyperthermia as cancer therapy has been studied with great enthusiasm, both clinically and experimentally. Some investigators have used a microwave antenna or radiofrequency current for hyperthermia of malignant brain tumors, but with these methods it is difficult to treat only the tumor without damaging normal brain tissue. The authors developed a system by which hyperthermia can be applied locally via an implant. Brain tumors were induced in rats by intracerebral implantation of T9 gliosarcoma cells (106 cells). Ten days after inoculation, a ferromagnetic seed was implanted in the tumor and a single application of hyperthermia was delivered. The temperature around the implant was maintained at 45.5±0.3°C for 30 minutes. The effect of a single treatment was assessed in terms of length of survival and morphological changes in the tumor.
The average survival time of the control group (n=23) was 20 days, whereas that of the treated group (n=27) was 29 days. The difference was statistically significant (p<0.01) . The pathological findings were as follows: 1) Immediately after hyperthermia, the tissue around the implant was necrotic, the intercellular spaces were enlarged, and the vessels were dilated. 2) In the long survivors, there were large areas of necrosis and accumulation of lymphocytes within the tumor tissue. 3) In one rat that survived, a large cavity was found where the tumor had been, and no tumor cells were detected on microscopic examination. 4) Immunohistochemical study with rat T cell monoclonal antibody demonstrated diffuse distribution of T lymphocytes within the tumor tissue. T lymphocyte subpopulations included helper and suppressor/cytotoxic T cells. These results are highly encouraging in terms of the potential for hyperthermia in the treatment of brain tumor.
