Abstract
Rationale: Radiation dose to patients from imaging modalities are measured or calculated to assess the risk of the procedure and compared it to the benefits. Periodic review of image acquisition methods and radiation dose used are essential part of procedure optimization in medical imaging. The aim of this study was to estimate patient radiation dose from single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) using computed tomography (CT) images for attenuation correction. Methods: SPECT and CT image acquisition parameters such as, administered activity (AA), CT dose index (CTDIvol) and dose-length product (DLP) of 415 patients who have undergone SPECT MPI using CT attenuation correction were reviewed. Effective dose (ED) for the SPECT part, CT part and the total ED for the procedure were calculated. AA, CTDIvol and ED values were compared between patient gender, body mass index, imaging scanner model and imaging centers. Statistical analyses were carried out using t-test and one-way analysis of variance at P < 0.05 level of significance. Results: The range of AA used for MPI was found to be 1206 to 1964 MBq per patient regardless of the gender. The resulting mean ED value of 8.8 mSv for males was significantly lower (P = 0.002) than 10.4 mSv for females in SPECT. The range of CTDIvol was 1.12 to 3.97 mGy resulting in mean ED of 0.8 mSv for males, significantly lower (p<0.001) than 1.1 mSv for females in CT. The average combined ED for male and female patients were 9.6 and 11.5 mSv respectively. Positive correlation was found between AA and patient body mass index (r=0.48; p<0.001), indicating patient size related AA. However, CTDIvol was found to depend only on the scanner model regardless of body mass index. Conclusion: The ED from SPECT-CT MPI studies was found to be around 11 mSv with 10 mSv from the SPECT part of the study. The extra risk to the patients from CT imaging for attenuation corrections is small compared to the benefits incurred in accurate diagnosis.