This is probably not going to help that much.
I have/had prostrate cancer, but mine was treated last year with nine weeks of daily radiation followed by two years of hormone therapy (which isn't fun either). I still have about 11 months of the hormone therapy. When I first talked to my Doctor about various treatments, he indicated that seed implants were not a good choice for me. I did have stomach cramps during the radiation treatment, but it tapered off when the radiation ended.
I think that all cases of prostrate cancer are different and there seems to be a wide selection of "protocol" treatments for them. Everyone in the radiation treatment waiting was getting a different, or slightly different, treatment and the range of reactions was varied.
hope you are able to get in touch with the Doctor to discuss this, but don't be greatly surprised if he/she tells you that the cramping is a common reaction. That was the answer virtually every time I mentioned an unpleasant side effect.
You and your husband have my deep sympathy as you deal with this long ordeal. But is the treatment was started early enough your husband should have a long life after this is over.