A microwave hyperthermia apparatus that can be inserted into the body which includes a hollow central tube for the insertion of radioactive therapy sources. The use of a coaxial transmission line impedance transformation along the insertable portion of the coaxial cable enables a reduction in the characteristic impedance by increasing the outer diameter of the inner coaxial conductor so that the center conductor can be a metal tube. If the ratio of the outer coaxial conductor diameter vs. the inner coaxial conductor is decreased, the characteristic impedance of the transmission line is lowered. This enables the inner conductor diameter to increase sufficiently to make the central hollow opening large enough to receive standard radioactive sources therein. This provides for a good impedance match that improves microwave energy efficiency while at the same time permitting a large hollow center opening. The combination of the microwave antenna device and brachytherapy sources provides for enhanced effectiveness when the two treatments are delivered simultaneously or in close time proximity to each other.