Intraoperative 3D navigation for single or multiple 125I-seed localization in breast-preserving cancer surgery

Background: Mammographic screening has led to the identification of more women with nonpalpable breast cancer, many of them to be treated with breast-preserving surgery. To accomplish radical tumor excision, adequate localization techniques such as radioactive seed localization (RSL) are required. For RSL, a radioactive 125I-seed is implanted central in the tumor to enable intraoperative localization using a γ-probe. In case of extensive tumor or multifocal carcinoma, multiple 125I-seeds can be used to delineate the involved area. Preoperative imaging is performed different from surgical positioning; therefore, exact 125I-seed depth remains unknown during surgery. Patients andMethods: Twenty patients (mean age, 56.8 years) with 25 implanted 125I-seeds scheduled for RSL were included. Sixteen patients had 1 125I-seed implanted in the primary lesion, 3 patients had 2 125I-seeds, and 1 patient had 3 125I-seeds. Freehand SPECT localized 125I-seeds bymeasuring γ-counts from different directions, all registered by an optical tracking system. Areconstruction and visualization algorithmenabled 3-dimensional (3D) navigation toward the 125I-seeds. Results: Freehand SPECT visualized all 125I-seeds in primary tumors and provided preincision depth information. The deviation, mean (SD), between the freehand SPECT depth and the surgical depth estimation was 1.9 (2.1) mm (range, 0-7 mm). Three-dimensional freehand SPECT was especially useful identifying multiple implanted 125I-seeds because the conventional γ-probe has more difficulty discriminating 125I-seeds transcutaneous. Conclusions: Freehand SPECTwith 3Dnavigation is a valuable tool in RSL for both single andmultiple implanted 125I-seeds in breast-preserving cancer surgery. Freehand SPECT provides continuous updating 3D imaging with information about depth and location of the 125I-seeds contributing to adequate excision of nonpalpable breast cancer.