I am making many guesses here.
Following brachiotherapy, your husband's blood test (PSI) has rapidly risen and the question is, has the cancer returned and has it spread to other parts?
Firstly a rise in PSI doesn't necessarily mean that the cancer has returned.
Secondly, the biopsy and MRI scan may give you the definitive answer.
Let us suppose that the cancer has returned,.The best management of the small number of prostate brachytherapy patients encountering failure is unclear at this time, but one could redo the brachytherapy with or without hormone treatment. Removing the prostate followed by hormone treatment is another option.
Wait for the results and the Oncologist/Urologist will discuss the options.