Establishing a relationship between temperature profiles and radiochemical purity when preparing Tc-99m sestamibi to determine optimal heating time for preparation

491 Objectives To gain a better understanding of the optimal labeling time for various heat sources used in the preparation of Tc-99m sestamibi by evaluating heating times and temperatures as they relate to the radiochemical purity of the final product. Methods All sestamibi kits evaluated in this project were prepared using 150 +/- 10 mCi of Tc-99m sodium pertechnetate and was prepared per manufacturer package insert preparation instructions in a total volume of 5ml. After addition of Tc-99m sodium pertechnetate, a temperature probe was insterted into the vials for measurement of the internal liquid temperature during the heating process. Following baseline temperature assessment, sestamibi kits were placed in either a rolling water bath or a heat block, both of which were preheated to appropriate temperature. Three sestamibi kits were heated for the package insert instructed 10 minute boiling time in each heat apparatus, with internal temperatures measured at each 1 minute time point during the boiling process to determine the maximum internal temperature during the heating process. After heating, the probe remained in the vial and temperature was tracked every minute for the first 10 minutes of the post boiling cooling process. Quality control testing using the package insert recommended procedure was performed immediately at the end of the boiling process as well as at the 5 and 10 minute points during cooling. Following the determination of the heat profiles for the package insert preparation method, further evaluation was undertaken to determine a more accurate boiling time requirement for these kits. For water bath samples, a variety of boiling times less than 10 minutes were evaluated, ranging from 0.5 minutes up to 8 minutes. For the heat block samples, boiling times greater than 10 mintues were evaluated - ranging from 11 minutes up to 20 minutes. All samples were evaluated using the same data collection procedure as used in the baseline temperature determination. Results Initial results show that the water bath, as anticipated, is the heating source which brings the internal temperature of the product to temperature much faster than the heating block. In tracking the relationship between temperature, time and radiochemical purity, acceptable radiochemical purity of the final product can be acheieved with significantly lower boiling times when using a water bath than are seen when heating with the heating block. In samples prepared in the heating block, acceptable radiochemical purity was not consistently achieved until after the recommended 10 minute heating step. Conclusions The radiochemical purity of Tc-99m sestamibi is dependent on a heating step to drive the reaction to completion. Inadequate heat delivery can lead to less than optimal radiochemical purity of the final product. The choice of heating apparatus varies, depending on operator preference and regulatory issues related to sterile product compounding. While both types of heating apparatus can be used to produce a final product of acceptable radiochemical purity, identifying the optimal parameters for heating Tc-99m sestamibi is essential in assuring the quality of the final product.