Optimization of (201)Tl Dosage in a Simultaneous Acquisition Rest (99m)Tc/Stress (201)Tl Dual-Isotope Myocardial Perfusion Single-Photon Emission Computed Tomography with Semiconductor Gamma Camera

Background: The use of (201)Tl in myocardial perfusion single-photon emission computed tomography (SPECT) is predominantly not recommended because of the higher radiation exposure of (201)Tl compared to (99m)Tc agent. However, the advent of new gamma cameras with semiconductor detectors has made it possible to reduce the (201)Tl dose and lower radiation exposure. In our hospital, the dose of (201)Tl is adjusted according to the patient's body mass index (BMI), with 50 MBq for BMI<25 and 74 MBq for BMI≥25. The dose of (201)Tl during simultaneous acquisition dual-isotope myocardial perfusion SPECT (MPS; stress (201)Tl and rest (99m)Tc agent) exceeds 9 mSv/examination when 74 MBq of (201)Tl is administered. In order to further reduce the radiation dose, optimization of the (201)Tl dose was investigated. Methods: Two hundred and eighty consecutive patients who underwent stress MPS using simultaneous acquisition dual-isotope protocol (SDI protocol) for the estimation of ischemic heart disease were included. Patients with prior myocardial infarction were excluded. Correlations between BMI and acquisition time were determined in patients receiving 50 MBq (n=154) or 74 MBq (n=126) of (201)Tl. In addition, linear regression analysis was used to determine the slope and intercept to derive a linear functional equation, and the theoretically optimal (201)Tl dose was evaluated. Results: The correlation coefficient between BMI and acquisition time in the (201)Tl 50 MBq group was 0.532 (P< 0.00001) and in the (201)Tl 74 MBq group was 0.478 (P<0.00001), both showing a positive correlation. Linear regression analysis yielded two equations: y=0.52x-0.32 ((201)Tl 50 MBq group) and y=0.41x-0.69 ((201)Tl 74 MBq group). Linear function equation results indicated that patients with BMI between 25 and 30 could be examined within approximately 15 minutes with 50 MBq of (201)Tl. Conclusion: Considering examination efficiency, a single acquisition time of less than 15 minutes is ideal. Theoretically, patients with BMI less than 30 could be examined within approximately 15 minutes with 50 MBq of (201)Tl.