WASHINGTONThe technique of radioactive seed
localization presents several important advantages over wire localization for
the diagnostic or therapeutic excision of nonpalpable breast cancers, said
Richard Gray, MD, of the H. Lee Moffitt Cancer Center and Research Institute,
Tampa, at the 54th Annual Cancer Symposium of the Society of Surgical Oncology
Dr. Gray described a prospective randomized trial indicating
that a radioactive seed technique localized tumors as effectively as the wire
technique but offered greater precision and convenience.
Though the wire technique is currently the standard method of
localizing non-palpable breast tumors, Dr. Gray noted, its disadvantages
include the need to do localization and biopsy on the same day, the chance of
displacement of the wires causing loss of localization, and the possibility of
excessive dissection. Other substitute techniques also present problems, he
said. Dye, for example, is inaccurate, and ultrasound techniques require
surgeons to learn new skills.
The radioactive seed technique involves loading a titanium seed
with 0.05 to 0.3 mCi of I125 into an 18-gauge needle. The surgeon then uses
sonographic or mammographic guidance to find the lesion and places the seed at
the site. Up to 5 days later, a hand-held gamma probe is used to show the skin
site directly over the lesion.
Because the seed is entirely within the breast, the radiologist
can use any angle without interfering with surgery, Dr. Gray noted.
Furthermore, he said, precise localization through the skin allows
reorientation during excision.
The final study involved 97 women, 51 of whom underwent seed
localization and 46 standard wire localization, he said. No significant
differences were found in pathology or in the time needed to localize or excise
the lesion. Neither seeds nor wires showed detectable migration, he added. The
radiologists and surgeons found no difference in ease of use, and there was no
difference in patient discomfort between the two techniques.
Significantly, though, wire localization resulted in a 50%
higher rate of positive excision margins than seed localization (P = .02).
"This suggests that seed localization is more precise," Dr. Gray
He noted that radiologists "love this technique"
because the seeds are closer to the lesion. The technique also indicates the
lesion’s exact depth. Dr. Gray suggested that this may be related to the
better margins it produces. If needed, two seeds can be used to bracket a
lesion, as in wire localization.
In addition to these benefits, the seed technique also permits
"better logistics," he said. Placement can take place up to 5 days
ahead of excision and does not interfere with sentinel lymph node mapping.
There is no excessive exposure to radiation, and seeds can be sterilized for
reuse. "Nuclear medicine is involved as far as storage of the seeds,"
he said, but radiologists and surgeons carry out the rest of the procedure. The
study did not analyze cost.
Although seed localization is still investigational, Dr. Gray
believes that the technique could also prove useful at other organ sites, such
as for marking colon polyps.