Lucy's Mom,
Any salvage treatment, either with surgery or radiation, are dependent on weather the disease is local or systemic. If systemic, outside the prostate gland and bed, no salvage treatments will work.
Primary treatments fail mostly because the disease is systemic.
In surgery local failures are caused by prostate tissue left behind after surgery or small positive margins that have leaked into the prostate bed. Radiation should take care of these as a primary treatment as radiation treats up to 15mm of the prostate bed and the entire gland.
Radiation local failure happen when too low a dose if given or in the rare case that the cancer cells are resistant to the isotope used. Normal external radiation is given in a dose of 81 greys which should kill most cancers; in the older radiation 65 greys were given and local faiures were more common. Combination brachy/IMRT is given in doses from 130 to 150 gy which is more than sufficient to kill almost all but the most agressive cancers. It also has two different isotopes in the event that one may be resistant.
For local radiation faiures reseeding with a different isotope, HDR Brachy and cryosurgery are the most common salvage treatments.
JohnT