what happen to prostate gland after SBRT treatment?

A number of things, but we really don't know for sure because no one will ever see the gland.

Basically, where the PCa was will eventually be either shed from your body and/or will turn to scar tissue. As cells die over time, they become waste and the systems will eliminate them from the body. The benign tissues that were radiated will change somewhat, but most will generally recover from the radiation. Depending on the extent of the PCa and radiation damage people experience various degrees of prostate function. If only a little of the prostate has been affected, then you may regain a lot of function. I had a high tumor load and a lot of radiation. Like many men, I have very little ejaculate due to diminished gland function.

As to the effect on urinary habits, I don't know what you should expect. Mine for the last seven years have been exactly what I experienced before the radiation. I never had problems, nor do I now. During the radiation period I did have the normal short term side effects of increased urgency and frequency, but that all subsided within a few weeks of the end of treatment.

Thank you all for the information. It is really helpful. I am glad to hear the urinary function will return to baseline or better within a year. Like most people, my ejaculate is much less after SBRT. Recently, my ejaculate changes from clear to white (or semi white). I was wondering it is a good sign (recovery) or a bad sign (not enough radiation)?