Background The Cadmium Zinc Telluride (CZT) detector is a direct conversion semiconductor for gamma cameras in nuclear medicine. Gamma rays directly produce electric charges which are collected by an electric field. The spatial and energy resolutions obtained with CZT detectors are better than scintillator-based gamma cameras. Thereby, patient exposure can be reduced. In our department, a reduction of 30 percent has been decided for the one-day protocol of myocardial perfusion imaging performed with 99mTc-tetrofosmin. In Europe, these scans are regulated by diagnostic reference levels (DRLs). For the one-day protocol of myocardial perfusion imaging performed with 99mTc-tetrofosmin, 300 MBq are needed for the first injection and 800 MBq for the second one. With scintillator-based gamma cameras, the DRLs are not respected, especially for heavier patients.
Purpose To determine the consequence of a dose reduction of 30% in terms of DRLs
Materials and methods All patients injected with 99mTc-tetrofosmin during the year following the arrival of the new heart-dedicated gamma camera with CZT detector were included in the study (n = 1963). Injected radioactivities were compared to the DRLs by a Wilcoxon test. The dose for a one-day protocol was 2.8 MBq/kg for the first injection with a minimum activity of 185 MBq and a maximum activity of 259 MBq. The second injection took place two hours later and the dose was 8.3 MBq/kg with a minimal activity of 555 MBq and a maximal activity of 777 MBq. As the radioactivity depends on weight, it was decided to group the patients according to their weight: small ≤65 kg, medium between 65 and 94 kg and high weight ≥94 kg.
Results For the first injection, the average radioactivities for small, medium and high weights were respectively 198.6/222/255 MBq, which means a dose reduction of 30, 25 and 14% compared to the DRLs (p < 0.01).
For the second injection, the average activity for small, medium and high weights were respectively 632.3/695.4/784.2 MBq, which means a dose reduction of 18, 12 and 0% compared to the DRLs (p < 0.001).
Conclusions The CZT detector gamma camera allowed us to keep below the DRLs for myocardial perfusion imaging regardless of the patient’s weight. Furthermore, the dose of radiation given by our one-day protocol is below the European Association of Nuclear Medicine’s guidelines, which are 400–500 MBq for the first injection and three times more for the second injection. Finally, this has improved patients and medical staff’s radiation protection.
No conflict of interest.
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