Time frame of sentinel node visualization in early breast cancer patients using intradermal injection of Tc-99m phytate: Imaging beyond 45 minutes does not yield more information

One of the major problems of lymphoscintigraphy is the time of patient presence in the nuclear medicine wards. The operating room schedule can be compromised if the patients stay longer than usual in the nuclear medicine departments. However, too early imaging can be falsely negative for sentinel node visualization and delayed imaging may be required. The aim of the current study is to determine a time beyond which lymphoscintigraphy imaging does not yield more information and imaging can be terminated.
One hundred and fifty women with proven clinically axillary node negative breast cancer entered the study For each patient 0.5 mCi Tc-99m phytate in the 0.2 cc volume was intradermally injected in periareolar region to raise a wheal. Lymphoscintigraphy imaging was done in the following time intervals: 5, 10, 30, 45, 60, 90 minutes post injection. In case of sentinel node visualization at any time, the imaging was terminated.
Sentinel nodes were first detected on 5, 10, 30, 45, 60, and 90 minute images in 31 (20.6%), 45 (30%), 46 (30.6%), 15 (10%), 1 (0.6%), and 0 patients. Median number of the detected sentinel nodes per patient was 1. At least one hot sentinel node could be identified in all 138 patients with observed sentinel nodes of whom, 45 had pathologically involved sentinel nodes and axillary lymph node dissection was done. In 12 patients, no sentinel node was visualized even on the 90 minute images. All of these patients had axillary node involvement and no sentinel node could be harvested intra-operatively either.
Considering the rather slow movement of Tc-99m phytate in the lymphatic system, lymphoscintigraphy imaging of the breast cancer patients should be continued for 45 minutes in case of sentinel node detection failure. On the other hand imaging beyond 45 minutes does not seem to be necessary as the diagnostic yield is very low.