The invention relates to the field of radiation oncology, specifically the use of novel radio-opaque fiduciary markers which resist migration within tissues, which may be implanted in the body and imaged during radio-therapy to insure accurate treatment of target regions while avoiding irradiation of non-target regions. In one embodiment, the markers comprise oblong bodies from which a plurality of short tines protrude. Also provided are novel devices for implanting such markers. Additionally, the invention provides methods of delineating tumor resection beds and whole-bladder contours in the radiotherapeutic treatment of bladder cancer. Lastly, the invention encompasses novel methods of delivering fiduciary markers and other implants and materials by needle with sealing aids that increase the retention rate of the delivered markers, implants, or materials.
