The present invention provides a means for achieving greater ability to negotiate small radii like 5 mm of curvature in the human body to treat tumors, for example, with radioactive materials. This is accomplished by incorporating the source capsule into a flexible housing, which, in its simplest configuration, eliminates the direct connection of the source capsule to the driving cable, adding a degree of flexibility that is not available with a direct connection of the source capsule to the driving cable as in the presently available source capsules, and further providing segmented source capsules, and further providing devices for shielding of tissue using the segmented source assemblies.