Dear vince,
Beta-radiation (also called brachytherapy) is the newest therapy for what is called "in-stent restenosis". There has been a lot of press about this recently because the FDA just approved a delivery device for this type of therapy. The therapy itself is still needs further investigation before it can be recommended for everyone. We are participating in ongoing trials of brachytherapy and those who are interested in this can call (216) 444-0770 for additional information.
In your particular case I don't think this therapy would probably not be a good idea because you already have the bypass grafts. If the grafts were to become blocked in the future you may be a candidate at that time.
Here are some review articles that have additional information.
In addition there is an article that was in the New England Journal of Medicine within the last few months that I don't have the reference for.
Crocker I. Radiation therapy to prevent coronary artery restenosis. [Review] [41 refs] Seminars in Radiation Oncology. 9(2):134-43, 1999 Apr.
Fischell TA. Radioactive stents. [Review] [18 refs] Seminars in Interventional Cardiology. 3(2):51-6, 1998 Jun.