Rufus,
Sorry to hear about your dad, but you haven't given enough information. It would be useful to put the history of the disease, tests (including PSA history), and treatments into your profile so people can read it before answering.
Is your father Stage 4 and running out of treatment options?
What has his consultant said?
What type of medical care is being provided?
Also, say if you're outside the UK, where treatments may be different.