A target tissue can be treated with a radioisotope. Some methods for treating a target tissue with a radioisotope include determining a distance between a target tissue and a surface of a matrix material to be positioned adjacent the target tissue and, based on the determined distance, determining an activity to be mixed with the matrix material to obtain a desired activity concentration. Some methods further include mixing the radioisotope with the matrix material. In some embodiments, the matrix material comprises bone cement, and the target tissue is a tumor in a bone. The radioisotope may be a beta-emitting radioisotope mixed in the cement at a concentration to form a radioactive cement.