2.4 Determination of Radiochemical Purity of Radiolabeled LymphoseekDetermine radiochemical purity of the reconstituted radiolabeled Lymphoseek by Instant Thin Layer Chromatography (ITLC) using either Whatman Grade 1, 3MM, 31ET Chr or Biodex 150-001 Red Strips (cellulose chromatography paper) using the following method:

a.Mark the chromatographic strip for origin, mid and solvent front lines with a pencil as shown below:

b.Apply a small drop (3 -- 10 microliters) of the reconstituted product at the center of the origin line chromatography strip. Let the product spot dry.
c.Place the strip into a chromatography chamber containing 1 mL of acetone as the developing solvent. Allow the solvent to migrate to the solvent front line (5 cm from the bottom of the Whatman strips and 3.5 cm for the Biodex strip). Remove the strip from the chamber, let it dry and cut it in half. Count each half of the strip with a suitable radioactivity counting apparatus (dose calibrator or multichannel analyzer).
d.Calculate the percent radiochemical purity (RCP) as follows:
% RCP = Counts bottom half x 100 Counts bottom half + Counts top half
e.Do not use the reconstituted Lymphoseek if the radiochemical purity is less than 90%.
Chromatograph
2.5 Lymphatic Mapping Procedures Following Injection of Lymphoseek ◦Lymphoscintigraphy may be considered to help plan the lymph node mapping procedures. In clinical studies, preoperative lymphoscintigraphy was performed in most patients; the extent to which lymphoscintigraphy contributed to the success of the mapping procedures was not established. [see Clinical Studies (14)]
◦Use a hand-held gamma counter to identify nodes that concentrated the injected radioactivity.
◦For intraoperative lymphatic mapping, first measure the background radioactivity counts from tissue at least 20 centimeters distal to the injection site. Use the three sigma threshold (background radioactivity counts plus three times the square root of the mean background count) as an estimate of the threshold for positive localization of Lymphoseek, as exemplified in Table 3.
Table 3. Examples of Estimates of the Three Sigma Threshold Value  a Average of three 2-second counts or one 10-second count 
Background Counta (cpm) Threshold Value (cpm)
5 12
10 20
15 27
20 34
25 40
30 47
35 53
40 59
a Average of three 2-second counts or one 10-second count 
Background Counta (cpm) Threshold Value (cpm)
5 12
10 20
15 27
20 34
25 40
30 47
35 53
40 59

◦Lymphoseek is intended to supplement palpation, visual inspection, and other procedures important to lymph node localization. Intraoperative lymphatic mapping by gamma detection of Lymphoseek within lymph nodes should be initiated no sooner than 15 minutes following injection of the final product. In clinical studies, patients also received a concomitant blue dye tracer to enhance the ability to detect lymph nodes. While most lymph nodes were detected with Lymphoseek, some were detected only with the blue dye tracer or only with palpation. [see Clinical Studies (14)]
◦The lymphatic system architecture and function may be changed by prior surgery, radiation, edema, inflammation or metastatic disease, and may result in chang