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

Abstract

PurposeThe aim of this study is to compare two routine protocols at our institution, CTPA and V/P-SPECT, in terms of radiation dose to the most exposed organs (lungs and breast) and to the embryo/fetus in the case of pregnant patients. MethodsAt our institution, the CTPA protocol includes a contrast enhanced CT (scan parameters: 100kVp, 700mA, 0.5s/rot, pitch 0.984) and in some cases a non-contrast enhanced CT acquisition (120kVp, 400mA, 0.5s/rot, pitch 1.375).In the V/P-SPECT protocol, ventilation SPECT was performed after inhalation of 99mTc-Technegas, reaching 30MBq in the lungs; perfusion was performed after intravenous administration of 60–120MBq of 99mTc-MAA.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 26–40weeks) using the web based calculation tool “COnceptus Dose Estimation” (CODE).Doses to organs and embryo/fetus from V/P-SPECT were estimated based on published dose data normalized to administered activity (mGy/MBq). ResultsEmbryo/fetus absorbed doses are similar for CTPA and V/P-SPECT and bellow 1mGy. The calculated dose to the lungs (breast) was 1.3–10.6 (27–136) times higher from CTPA when compared with V/P-SPECT. ConclusionFor 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.