Some preparations of 99mTc-colloidal rhenium sulfide (Nanocis) contain excess free pertechnetate (99mTcO4−) impurity (>5%).
To improve the radiochemical purity of Nanocis preparations and the quality of preoperative lymphoscintigraphy in sentinel node localization of breast cancer patients, we investigated the effects of temperature on the presence of free 99mTcO4− and nanocolloid size modification.
A Nanocis kit was reconstituted with sodium pertechnetate (650–850 MBq) in a final volume of 3.5 ml and heated for 30 min at 100, 115, or 130°C. The radiochemical purity was determined by paper chromatography, in triplicate. The particle size was evaluated by membrane filtration through a 200-nm and 100-nm filter. The preoperative lymphoscintigraphy images were acquired about 2 h after tracer administration.
Significantly higher radiochemical purity values were observed with 28 Nanocis preparations heated at 130°C (median: 99.8%, min–max: 97.0–99.9%) compared with values from 37 Nanocis preparations heated at 100°C (median: 96.3%, min–max: 85.2–99.5%) or 26 Nanocis preparations heated at 115°C (median: 95.1%, min–max: 85.7–99.8%). The interbatch variations of the radiochemical purity were reduced at 130°C. A high temperature level (130°C) did not modify the particle size. In lymphoscintigraphy, free 99mTcO4− uptake by the thyroid or stomach, which was sometimes observed with a Nanocis preparation heated at 100 or 115°C, was never visualized with a Nanocis preparation heated at 130°C.
These results indicate that increasing temperature from 100 to 130°C can be used in routine clinical practice to improve the radiochemical purity of the Nanocis preparation.