Further optimisation of 99mTc-Nanocoll sentinel node localisation in carcinoma of the breast by improved labelling

The sentinel node (SLN) procedure has gained widespread acceptance for the axillary staging of patients who present with carcinoma of the breast. A first series of 21 patients were imaged 2 and 4 h after the injection of technetium-99m colloidal albumin. Preoperatively, axillary foci were located scintigraphically and with a hand-held gamma probe that was also used to detect the radiolabelled nodes 22 h later in the operating theatre. In a high percentage of our first series it was difficult to localise the sentinel node owing to a low count rate ex vivo. The aim of this study was to facilitate the detection of sentinel nodes by improving the count rate by the use of higher specific concentrations of 99mTc-colloidal albumin, with increased radiochemical labelling efficiency and stability. In vitro tests were performed to establish the radiochemical labelling efficiency and stability of different concentrations of 99-mTc-colloidal albumin. Concentrations of 2.5, 10, 20, 25, 30, 37 and 50 MBq 99mTc/microg colloidal albumin (Nanocoll) were prepared under nitrogen and in vacuum. The quality of the solutions was assessed by testing the radiochemical labelling efficiency and stability after 0.5, 2, 5, 8 and 24 h. The particle size of colloidal albumin was tested by dynamic light scattering at 30.2 degrees, 62.6 degrees and 90.0 degrees angles. Following the results of the in vitro studies, higher concentrations of 99mTc-colloidal albumin were used in vivo in a further series of 98 patients. For labelling under nitrogen, a maximum acceptable concentration of 10 MBq/microg was found, which complies with the specifications of the manufacturer. By preparing the labelling in vacuum vials, a 2.5 times greater radiochemical labelling efficiency over the entire period was achieved, and a significant improvement (P<0.002) in the in vivo series was found. It is concluded that although the rate of successful visualisation of the SLN was high in all studies, a better count rate (nine times higher) was achieved with the highest concentration of 99mTc-colloidal albumin, which facilitated the detection of the SLN by the gamma probe during surgery.