COMPARISON OF 4 ALTERNATIVE RADIOCHEMICAL PURITY TESTING METHODS FOR TC-99(M)-SESTAMIBI

Four different methods for determining the radiochemical purity (RCP) of Tc-99(m)-sestamibi have been proposed to replace the recommended thin-layer chromatography (TLC) method, as the recommended method is inconvenient and time-consuming. The purpose of this study was to compare the recommended TLC method with the four proposed rapid QC methods for Tc-99(m)-sestamibi: (1) chloroform extraction (CE), (2) mini-paper chromatography with chloroform/tetrahydrofuran (1:1, v/v) (MPC), (3) Waters(TM) Sep-Pak(R) alumina N cartridge with 100% ethanol (SPE), and (4) Waters(TM) Sep-Pak(R) C18 cartridge with normal saline (SPNS). For RCP values ranging from 21.8 to 98.7% (n = 20), both the CE and SPNS methods produced falsely high RCP values (RCP difference: 14.1 +/- 23.5% for CE and 15.0 +/- 24.9% for SPNS). The MPC and SPE methods were in good agreement (r = 0.98 for MPC and 0.88 for SPE) with the recommended TLC method over the critical RCP range (i.e. 77.0-98.7%, n = 52) (RCP difference: -0.9 +/- 1.2% for MPC and -4.3 +/- 3.2% for SPE). None of the Tc-99(m)-sestamibi preparations that had been rejected (i.e. RCP <90%) by the TLC method were accepted by either the MPC or SPE method. However, 4 of the 52 Tc-99(m)-sestamibi preparations with acceptable RCP by the TLC method had unacceptable RCP by the MPC method, whereas 8 of the same 52 preparations were unacceptable by the SPE method. The SPE method requires the loading of 0.05-0.1 ml Tc-99(m)-sestamibi to the cartridge, which may consist of up to 1.2 GBq (33.3 mCi) Tc-99(m) activity per application (based upon the 37 GBq or 1000 mCi/3 mi per kit preparation). The MPC method takes only a 5 mu l sample (9.3 MBq or 250 mu Ci) and 3-4 min for each RCP analysis. In conclusion, the MPC method is the best alternative method for the RCP determination of Tc-99(m)-sestamibi, especially in emergency situations.