I'm sorry to hear about your father's condition.

I'm not a doctor but here is a possible theory about what is happening.
The removal of the testicles removed the source of 90-95% of the
testosterone in your father's body.  Eventually, in most men,
"hormone refractory" cancer cells will begin to grow in spite of the
reduction of testosterone.  The Lupron injection probably suppressed
the remaining testosterone and had a small positive effect, but
by the time the Lupron was given, the hormone refractory cancer may
already have become a significant part of the total amount of cancer
in the body.  If so, the Lupron injection was probably worth doing
because it may have added a few months of life, but it wouldn't do
much and not do it for very long.

I do not remember whether your father had any treatment other than
removal of the testicles and Lupron.  Did he have a prostatectomy
operation to remove the prostate, or radiation to "de-vitalize" it?  If
not, those treatments might cure him - if the cancer has not spread
beyond the prostate region.

If the cancer has already spread outside the prostate region, then
what your father's doctor has already done is probably all that can
be done.

There are some experimental treatments being tested in the U.S. that
might, or might not, add a small amount of time (weeks or months) to
a prostate cancer patient's life but, to my knowledge, there are no
cures and nothing that is even known for sure to be of significant help.

There is evidence that good diet and exercise may help to prevent
cancer but, to my knowledge, diet and exercise are not alone able
to prevent it, and cannot cure it after it's there.  I am not aware of any
studies showing that special diets will even slow down the growth of
the cancer - though some doctors seem to recommend good diets
as a way to keep the body as healthy as possible regardless of the
presence of cancer.

I wish the best for you and your family.

Good luck,

   Alan