New technology that has replaced the old radioisotope What technology has the radioisotope Cobalt 60 replaced in medicine?

E.g.,PET preferred over CT scans
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.