There are a couple of websites you can use that explain both permanent seeds brachytherapy (LDR) and High Dose Rate brachytherapy (HDR). For seeds see
www.prostrcision.com and for HDR see
www.cetmc.com.
I don't remember any under 50 members using radiation as a frontline treatment, but there are many that had surgery then used radiation (usually external beam) as salvage. In my opinion, many could have used brachytherapy (either LDR or HDR) and external beam radiation (IMRT/IGRT) and saved themselves the trouble, side effects, and risk of surgery.
It is interesting to me that so many uros will advise a man under 50 not to use radiation as a frontline treatment due to the young age, but advocate it as salvage when surgery fails. In almost every other non-blood cancer, radiation is often part of primary or adjuvant therapy regardless of age, but not prostate cancer.