Feasibility of preoperative (125)I seed-guided tumoural tracer injection using freehand SPECT for sentinel lymph node mapping in non-palpable breast cancer

BACKGROUND: This study was designed to explore the feasibility of replacing the conventional peri-/intratumoural ultrasound (US)-guided technetium-99m albumin nanocolloid ((99m)Tc-nanocolloid) administration by an injection of the same tracer guided by a freehand single-photon emission computed tomography (SPECT) device in patients with non-palpable breast cancer with an iodine-125 ((125)I) seed as tumour marker, who are scheduled for a sentinel lymph node biopsy (SLNB). This approach aimed to decrease the workload of the radiology department, avoiding a second US-guided procedure. METHODS: In ten patients, the implanted (125)I seed was primarily localised using freehand SPECT and subsequently verified by conventional US in order to inject the (99m)Tc-nanocolloid. The following 34 patients were injected using only freehand SPECT localisation. In these patients, additional SPECT/CT was acquired to measure the distance between the (99m)Tc-nanocolloid injection depot and the (125)I seed. In retrospect, a group of 21 patients with US-guided (99m)Tc-nanocolloid administrations was included as a control group. RESULTS: The depth difference measured by US and freehand SPECT in ten patients was 1.6 ± 1.6 mm. In the following 36 (125)I seeds (34 patients), the average difference between the (125)I seed and the centre of the (99m)Tc-nanocolloid injection depot was 10.9 ± 6.8 mm. In the retrospective study, the average distance between the (125)I seed and the centre of the (99m)Tc-nanocolloid injection depot as measured in SPECT/CT was 9.7 ± 6.5 mm and was not significantly different compared to the freehand SPECT-guided group (two-sample Student's t test, p = 0.52). CONCLUSION: We conclude that using freehand SPECT for (99m)Tc-nanocolloid administration in patients with non-palpable breast cancer with previously implanted (125)I seed is feasible. This technique may improve daily clinical logistics, reducing the workload of the radiology department.