Radio-guided seed localization for breast cancer excision: an ex-vivo specimen-based study to establish the accuracy of a freehand-SPECT device in predicting resection margins

PurposeRadioactive seed localization (RSL) uses an iodine-125 (125I) seed as a marker for tumour location. The 125I seed is implanted into the tumour and enables intraoperative localization with a conventional gamma probe. However, specimen margins in relation to the 125I seed are estimated on the basis of gamma-probe readings only. A novel device, freehand SPECT, is capable of measuring the distance from the resection plane to the 125I seed. The aim of this feasibility study was to establish the accuracy of this device in predicting resection margins in ex-vivo tumour specimens excised with RSL guidance. Patients and methodsIn this feasibility study 10 patients with nonpalpable breast cancer scheduled for wide local excision with RSL were included. After surgery, the specimens containing the breast tumour and the 125I seed were scanned using freehand SPECT. Measurements from five directions were taken and compared with distances measured by means of an ex-vivo computed tomographic (CT) scan and related to the pathology report. ResultsThe difference between freehand SPECT and CT measurements was 2.9±2.7 mm (mean±SD). One patient had a positive margin based on freehand SPECT. This specimen contained a focal irradical resection ventral of the tumour based on the pathology report. The smallest distance to the 125I seed was 4 mm for the freehand SPECT and 5 mm for the CT scan. ConclusionAccurate ex-vivo measurements of the tumour resection margins using 125I seeds and freehand SPECT are feasible in patients undergoing breast-conserving surgery. Incorporation of the freehand-SPECT device in RSL protocols may enable a real-time estimation of resection margins, which may be useful for surgeons to adjust resection planes.