Hi, after radiation almost anything can happen. What type of radiation did your husband receive?
SBRT (Cyberknife, etc) and HDR brachytherapy +SBRT use very high doses of radiation and swelling and inflammation can follow.
Also, if your husband had urinary issues before radiation, slow or weak stream, BPH, this will be exacerbated by radiation. Many times, these issues are addressed BEFORE radiation, since they will only become worse after treatment.
Unfortunately, until that internal swelling subsides, self - catheterization, while unpleasant, may be the only solution.
I’m mot a doctor, just relating what I’ve learned thru my own experience and that of others. Best,
Phil