This paper presents a combination of three computational methods in a hybrid approach designed to model the radiation of antennas within arbitrarily shaped capsules implanted in a host body. A surface method of moments is employed to represent the radiation source, offering the advantage of a low number of unknowns, as well as enabling evaluation of performance limitation and topology optimization. The volumetric method of moments is applied to model the antenna's surroundings, including the antenna encapsulation. To reduce the use of the more computationally demanding volumetric method of moments, a spherical vector wave expansion is used to describe the host body.