I'm amazed that anyone as prestigious as Memorial Sloan Kettering investigated this. They used an ultrasound probe up the butt of 20 men implanted with I-125 seeds, and 82 men implanted with Pd-103 seeds at the day of implantation and also 60 days later. The dose received by the probe (i.e., the top's penis) was not high enough that they recommend complete abstinence, but they do recommend limiting fucking for 6 months if I-125 seeds were implanted and for 2 months if Pd-103 seeds were implanted. Here's a link to their study: brachyjournal.com/article/S...
They don't mention the bottom's POV, but if it feels painful (in a bad way), stop. Those tissues are apt to be raw for quite a while after implantation, and you want to give them some time to heal. I asked my RO if there is a danger of driving seeds into the urethra, and he didn't think so, but no one has studied that. No one has tracked the effect on seed migration. I'd certainly want to wait for the inflammation to go down and scar tissue to set the seeds in place, which would be at least 2 weeks for Pd-103 seeds and a month for 1-125 seeds.
- Allen