Prostate cancer is different to some other cancers in that it is not necessarily limited to the one suspect section of the gland, and the full extent of the cancer is often not known for sure until after it is removed and examined.
To a limited extent some treatment options like the HIFU mentioned are currently used in a basic way to treat the suspected affected areas. Unlike surgery, HIFU is a less invasive treatment that can be repeated if necessary.
This could well be a future way, but for now it is not a generally vaiable option to treat just one suspect section of the prostate.