Seeds may be referring to as used in prostrate cancer, and are seed like and or the beads that are used in a hollow tube for brachytherapy, interstitial believe. As mentioned, we probably seen more of this in the recurrence setting, but Brachytherapy is in the NCCN Guidelines for definitive radiation treatment for oral cavity cancer, although IMRT is preferred.
Here is more info for resource purposes.
http://en.m.wikipedia.org/wiki/Brachytherapy