Side effects from permanent seed brachy typically peak after 1-2 months, but usually reduce after a couple more months. Some side effects take longer to show up.
See the Permanant Seed Brachytherapy publication.
By the way, assuming it was seed brachy (rather than HDR brachy), your husband's brachy treatment started 2 months ago. It continues until the seeds run low on radioactivity, which will be a year or so. The seeds most commonly used lose half their radioactivity every 3 months, so that's 50% gone at 3 months, 75% at 6 months, 88% at 9 months, 94% after a year, etc.