Diagnostic reference level, achievable dose, and effective dose estimation in adult hybrid SPECT myocardial perfusion imaging in Institut Jantung Negara.

This study aims to establish the diagnostic reference level (DRL), achievable dose (AD), and effective dose (ED) estimation for adult hybrid SPECT myocardial perfusion imaging (MPI) procedures at Institut Jantung Negara (IJN). 737 subjects referred for MPI studies from January to June 2024 were included in the analysis. These subjects underwent either a one-day or two-day Tc-99 m tetrofosmin protocol using a cardiac-dedicated single-photon emission computed tomography (SPECT), either GE SPECT Discovery NM530c or GE SPECT Ventri. All subjects also underwent a cardiac CT scan via an external positron emission tomography/computed tomography (PET/CT) system, GE Discovery MI Digital Ready for either CT attenuation correction (CTAC) or CT coronary artery calcium score (CAC) protocol, depending on their clinical condition. The one-day protocol showed AD of 240.50 MBq and 691.90 MBq for the first and second injections, respectively, with corresponding DRL of 263.63 MBq and 777.93 MBq. The two-day protocol involved higher ADs of 1106.30 MBq and 1073.00 MBq for the first and second injections, with DRL of 1239.50 MBq and 1221.00 MBq, respectively. In the CTAC protocol, the AD for CT dose index volume (CTDI) was 2.8 mGy, with a DRL of 4.3 mGy. The dose length product (DLP) had an AD of 53.1 mGy.cm, compared to a DRL of 78.6 mGy.cm. For the CAC protocol, the CTDI had an AD of 4.8 mGy, matching the DRL of 4.8 mGy. The DLP showed an AD of 67.8 mGy.cm, with a DRL of 77.5 mGy.cm. The mean cumulated effective dose (ED) for one-day/CTAC, one-day/CAC, two-day/CTAC, and two-day/CAC was 6.69 ± 1.76 mSv, 7.32 ± 1.37 mSv, 10.13 ± 5.31 mSv, and 13.99 ± 3.24 mSv respectively. The average ED relative contribution by SPECT and CT were found to be 78.3% and 21.7% respectively. The DRL, AD, and ED data were successfully established for local MPI practice, contributing to global efforts to harmonize and enhance radiation safety in MPI practices.