New technology that has replaced the old radioisotope
After searching on Google (now there's an idea)...

If you are asking about what technology was used in medicine before Co-60 therapy was developed:

Co-60 therapy was developed in the early 1950's and was seen as an alternative to other forms of X-ray radiotherapy, or radiation therapy. It is a form of external beam radiation therapy. Radiation sources at the time (mostly derived from radium) required very high energy sources, and proved largely ineffective against deep-set cancers. Co-60 therapy was able to penetrate deeper at lower energies, and therefore was more effective against a range of previously untreatable cancer types. The first Co-60 machine was from the The University of Saskatchewan, and they have an excellent site devoted to the history of Co-60 treatment. 

If you asking about what technology is now being used in place of Co-60 therapy:

Conventional X-ray sources were improved with the development the linear accelerator which could produce X-ray energies exceeding 8MV. Nowadays, commercial units can produce photons up to 25MV. Here is a useful link to compare linear accelerator and Co-60 radiation sources for medical applications. There are still many developing areas of use, with some experts claiming there is still very much a place for Co-60 therapy. Co-60 therapy can be applied with high precision with low side-effects and is just one of many approaches available, often used in tandem with other medical treatments.