It is generally suggested to refrain from any activity that causes jostling (m/c, bicycling, horses) for 4-6 months after seed implantation. This motion could cause seed movement or swelling.
(btw- I'm a radiologist(retired), NOT a radiation therapist, so I would defer to his judgement).
(btw- I'm a radiologist(retired), NOT a radiation therapist, so I would defer to his judgement).