SPECT-CT in routine clinical practice increase in patient radiation dose compared with SPECT alone

Objective To assess the patient radiation dose during routine clinical single-photon emission computed tomography-computed tomography (SPECT-CT) and measure the increase as compared with SPECT alone. Materials and methods Data pertaining to 357 consecutive patients who had undergone radioisotope imaging along with SPECT-CT of a selected volume were retrospectively evaluated. Dose of the injected radiopharmaceutical (MBq) was noted, and the effective dose (mSv) was calculated as per International Commission on Radiological Protection (ICRP) guidelines. The volume-weighted computed tomography dose index (CTDIvol) and dose length product of the CT were also assessed using standard phantoms. The effective dose (mSv) due to CT was calculated as the product of dose length product and a conversion factor depending on the region of investigation, using ICRP guidelines. The dose due to CT was compared among different investigations. The increase in effective dose was calculated as CT dose expressed as a percentage of radiopharmaceutical dose. Results The per-patient CT effective dose for different studies varied between 0.06 and 11.9 mSv. The mean CT effective dose was lowest for Tc-99m-ethylene cysteine dimer brain SPECT-CT (0.9 +/- 0.7) and highest for Tc-99m-methylene diphosphonate bone SPECT-CT (4.2 +/- 2.8). The increase in radiation dose (SPECT-CT vs. SPECT) varied widely (2.3-666.4% for Tc-99m-tracers and 0.02-96.2% for I-131-tracers). However, the effective dose of CT in SPECT-CT was less than the values reported for conventional CT examinations of the same regions. Conclusion Addition of CT to nuclear medicine imaging in the form of SPECT-CT increases the radiation dose to the patient, with the effective dose due to CT exceeding the effective dose of RP in many instances. Hence, appropriate utilization and optimization of the protocols of SPECT-CT is needed to maximize benefit to patients. Nucl Med Commun 33:926-932 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.