The present invention relates to a process of thermal treatment in a tissue, and especially relates to a process of thermal treatment in a tissue comprising embedding a heat-sensitive magnetic material (hereinafter referred to as "implant") in a tumor, and externally applying a high frequency magnetic field thereto for raising the temperature of the implant in order to promote the medical treatment.
A process of thermal treatment in a tissue is one in which high frequency induction heating is utilized for medically treating a tumor in a living body in which a plurality of needle-like implant elements are embedded, based on the therapeutic effects which destroy only cancer cells to minimize the unfavorable influence on normal cells when the temperature of tissues of an organism is elevated to 42.degree. C. to 43.degree. C. The process of thermal treatment in a tissue is supposed to be promising not only for a brain tumor but also for other internal organ cancers such as a tongue cancer, a spleen cancer, a bladder cancer, a bone tumor, a mammary cancer and [Tatsuya Kobayashi, Yoshihisa Kida, Masaaki Matsui and Yoshifumi Amamiya, NEUROLOGICAL SURGERY, Vol. 18, No. 3 (issued on Mar. 10, 1990)]. A metallic alloy such as a Ni-Cu alloy, a Ni-Si alloy, a Ni-Pd alloy, an Fe-Pt alloy, an Fe-Pd alloy and an Fe-Pt-Si alloy and an oxide such as .gamma.-hematite, magnetite, cementite, rare earth magnetic materials, strontium ferrite, magnet-plumbite type ferrite and amorphous materials are known as material of the implant element employed in the process of thermal treatment (Japanese patent laid open gazette No. 63-103048).
Heat generation of the above implant material of the metallic magnetic material is carried out by mainly utilizing eddy current loss, while that of the magnetic material made of an oxide or that of the powders of metallic materials are carried out by mainly utilizing magnetic hysteresis loss of powders. When the eddy current is utilized, the magnetic field is required to be applied in the longitudinal direction of a cylindrical sample for avoiding the influence of a demagnetizing field. For avoiding the directional influence of the magnetic field, the magnetic field may be rotated utilizing a Helmholz type coil which generates a magnetic field by parallel connecting the same sized coils to provide a space in the middle. Such properties as a sufficient amount of heat generation, a relatively low Curie temperature and the safety in an organism are required as implant material. It has been conventionally supposed that an Fe 73% (atomic %, any percentage appearing in the rest of the specification is also atomic %)- Pt 27% alloy having a low Curie temperature of 68.degree. C. is most suitable.
Since, however, even the temperature of the implant element made of the Fe-Pt alloy itself rises to 68.degree. C., there is a possibility of damaging the normal cells as well as the cancer cells by means of the heat generated. When the implant element made of the Ni-Cu alloy or the Ni-Si alloy having a similar Curie temperature to that of the Fe-Pt alloy is employed, a large number of the implant elements are required to be embedded in an affected part because of the insufficient heat generation. On the other hand, in case of the bulk-like molded material made of the powders utilizing the hysteresis loss, there are disadvantages such that when the high frequency magnetic field is applied, an eddy current flows at a contacted portion to prevent the sufficient penetration of the magnetic flux into the implant element so as to suppress the generation of heat by means of the hysteresis loss that results in the uneven heat transmission to the affected part. Although the amount of the heat generation is desirably changed according to the individual difference of a patient and the progress of the affected part, it is in fact impossible.
Further, the compatibility of the implant element to an organism including the dispersion of the component elements into the organism as a result of corrosion and ionization is problematic even if such a metal as Fe and Pt is a metal of considerably low toxicity because the implant element is embedded in the organism for a long period of time. The molded member made of powders such as ceramics becomes brittle after the repetition of the thermal treatments in a tissue so that the uncovered powders are in danger of straying in the living body.