SPECT/CT assessment of sentinel lymph node reproducibility in breast cancer

1482 Objectives To evaluate the reproducibility of radionuclide sentinel lymph node (SLN) localization in breast cancer with SPECT/CT images. Methods All the patients with breast cancer that underwent SLN lymphoscintigraphy with SPECT/CT in the last 5 years in our clinic were reviewed. Those who were submitted to the procedure in two consecutive occasions due to suspension of the surgical intervention for different reasons (insufficient fasting, respiratory infection, hypertension, coordination problems) were included. Patients with prior breast surgery or excisional biopsy were excluded. A total of 10 female patients (mean age 52 years, range 36-83) were identified. The routine procedure consisted on the subdermal periareolar injection of 37-72 MBq (1-2 mCi) of 99mTc-nanocolloid in 0.2 ml in the same quadrant of the tumor followed by 5 minutes of axillary lymphatic massage, anterior and lateral planar images and SPECT/CT images in an Infinia Hawkeye 4 gamma camera. Acquisition was performed in a 180° orbit in 32 steps from anterior to posterior of the corresponding axilla, selecting a 128 x 128 matrix with a pixel size of 4.42 mm, immediately followed by low-dose CT (140 keV, 2.5 mA, 1.9 pitch). SPECT images were processed with OSEM in a Xeleris 2 workstation. CT-based attenuation correction was always performed. The correlation between the two methods in terms of location and number of lymph nodes detected was analyzed. Results At least 1 SLN was detected in all patients. A total of 20 SLN (average 2 SLN/patient) were identified. Regarding location, 14 SLN belonged to the lateral axillary group, 4 to the central and 2 to the apical group. The SLN detected by patient were 1 in 6 cases (all of the lateral group), 2 in 1 case, 3 in 1, 4 in 1 and 5 in 1. No extra-axillary nodes were observed. Intra-patient comparison revealed concordance between the two consecutive studies in the topography of the SLN in all cases. Two cases presenting 1 SLN of the lateral group in one procedure showed and additional node of lower uptake in the central group in the second procedure. The correlation was 100% in those patients who had more than one SLN, not only in number, but also in location and intensity of uptake visually interpreted. Conclusions The technique showed 100% reproducibility in the group studied. Just a second lymph node of lower uptake was detected in two cases. The concordance persisted even in patients who showed several SLN, suggesting that the main factor responsible for the number of SLN observed is the intrinsic variability of the lymphatic drainage between patients, beyond differences in the technical conditions of the procedure. The reproducibility of the lymphatic drainage of the breast is a fundamental premise behind this procedure, but only a few studies previously assessed this issue, all of them using planar lymphoscintigraphy. SPECT/CT provides enhanced sensitivity and precise anatomic information that make it an ideal method to assess reproducibility in larger series.