Radiation dose comparison between V/P-SPECT and CT-angiography in the diagnosis of pulmonary embolism

Purpose: The aim of this study is to compare two routine protocols at our institution, CTPA and V/PSPECT, in terms of radiation dose to the most exposed organs (lungs and breast) and to the embryo/fetus in the case of pregnant patients. Methods: At our institution, the CTPA protocol includes a contrast enhanced CT (scan parameters: 100 kVp, 700 mA, 0.5 s/rot, pitch 0.984) and in some cases a non-contrast enhanced CT acquisition (120 kVp, 400 mA, 0.5 s/rot, pitch 1.375). Methods: In the V/P-SPECT protocol, ventilation SPECT was performed after inhalation of 99mTcTechnegas, reaching 30 MBq in the lungs; perfusion was performed after intravenous administration of 60-120 MBq of 99mTc-MAA. Methods: The absorbed doses (mGy) to lungs and breast from CTPA were estimated using the ImPACT CT Patient Dosimetry Calculator. The embryo/fetus dose was estimated for different gestational stages (0-7, 8-12, 13-25 and 26-40 weeks) using the web based calculation tool `` COnceptus Dose Estimation (CODE). Methods: Doses to organs and embryo/fetus from V/P-SPECT were estimated based on published dose data normalized to administered activity (mGy/MBq). Results: Embryo/fetus absorbed doses are similar for CTPA and V/P-SPECT and bellow 1 mGy. The calculated dose to the lungs (breast) was 1.3-10.6 (27-136) times higher from CTPA when compared with V/PSPECT. Conclusion: For the diagnosis of PE in women, if both imaging modalities are available, it is recommended to proceed with V/P-SPECT rather than CTPA due to the considerably lower radiation dose to the breast. (C) 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.