The fossa (bed) of the prostate is indeed the bottom face of the
bladder wall. This needs carefully planned radiation to prevent damage
to the bladder and even possibly bladder cancer.
Other salvage radiation is aimed at the pelvis to pick up on the lymph
nodes and any other suspect adjacent areas.
There appears to be no definitive tumour target areas.
Usually the radiation is supplemented with ADT (hormonal therapy.)

There are several guys in this NG on Salvage Therapy, so they may be
able to respond with more accuracy.

If you study Dr. Catalona's Q&A section you'll find some answers.

Here!:-   http://www.drcatalona.com/quest/quest_spring03_3.htm 

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Looks like you've gotten great answers (as is the norm here).  I would add
two things.

One, only of interest, I guess, is that the radiation isn't like radiation
of old where they actually 'aimed' radiation from cobalt at the general
direction of a tumor.  What is really going on in EBRT is a partical
accelerator is shooting particals through the body at such a rate that
radiation is generated (or at least that's how I understand it).  When the
gun is turned off, there is no more radiation.

Two, the worst side effects are feared to occur sometime down the road.  I
worry that I will be cured of PCa in 2015 and die of colon cancer in 2020.

"Where the prostate was is now filled with the bladder that drops down
into the void (little Willie grows back to normal size)"

I don't believe that is the case since they yank the urethra up and
connect it to what's left of the bladder neck. It may drop down and
give you a little but not normal size. :-(

Bill Denton
RP 2/12/02
PSA >.6
Memphis

Dose Level: Should be 64 or above. The higher the better. 68,400 is what was
given to me. My surgeon wanted me to get 72,000. My Rad/Onc wouldn't go for
it stating that doses at 70,000 and above cause problems for salvage
patients. Urinary/Bowel problems.

Dose was given daily for  38 days at 1,800 rads per day = 68,400

They know exactly where to shoot - since they take dozens and dozens of
xrays-pictures-3d images throughout the process.

I believe the Doc told me that some areas - like where I had my positive
marin received much more of a dose than 68,400.

They have it all mapped out if you want to see it - your prostate region -
and what area's received what amount of radiation.

Doc stated that the treatment given now with the new techniques - especially
the imaging - performed by the physicist - is light years away from even
what was provided in the early 2000's. The new machines make a substantial
difference - but it is your physicist with the imaging techniques that
really has provided the potential for great results.  So make sure you have
a great physicist/science person.

To be honest. I am starting to get a bit angry with the hormone and
radiation treatments. WE need new treatments now. We all need to start
lobbying and encouraging others to lobby for more research and treatment.
Putting some pressure on our legislatures and making some noise. It's been
30 years of these treatments. It reminds me of the oil and energy crisis.

We are getting closer though. Everybody hold on to your hope. Some guy/gal
will cure this disease soon.

Dave P