Program Information
Pulmonary CT Angiography and Ventilation/perfusion SPECT: Breast Radiation Dose Considerations
E Tonkopi*, A Ross , E LeBlanc , Queen Elizabeth II Health Sciences Ctr, Halifax, NS
Presentations
MO-RPM-GePD-I-4 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Imaging ePoster Lounge
Purpose: To measure breast radiation dose received from different CT pulmonary angiography (CTPA) protocols and to compare with ventilation perfusion (V/Q) scan dose.
Methods: A thorax anthropomorphic chest phantom was scanned with eight clinical CTPA protocols implemented on three CT scanners in our institution. Either organ-based tube current modulation (TCM) or bismuth shielding were utilized in each scan for breast dose reduction. Dose to the breast was measured with a RaySafe Xi dosimeter placed at the mid-sagittal line on the anterior surface of the phantom. Effective dose was estimated using dose-length product values and the conversion factor of 0.014 mSv/(mGy∙cm) for adult chest. Radiation dose for the SPECT V/Q was calculated using organ doses per unit administered activity for the pharmaceuticals listed in the ICRP Publication 128. Typically, 185 MBq of Technetium-99m MAA is used for the perfusion portion of the study, and 40 MBq of Tc-99mTechnegas is absorbed in the lungs for imaging in the ventilation portion.
Results: The V/Q scan resulted in a breast dose of 1.20 mGy and an effective dose (ED) of 2.64 mSv. For the CTPA study, the lowest dose (breast: 2.09 mGy, ED: 0.94 mSv) was achieved on the dual source (DS) CT scanner allowing a high pitch of 1.55. This technique is not suitable for large patients due to the field of view restriction. For other CTPA protocols the breast dose was in the range of 7.12–27.68 mGy, and the effective dose varied from 4.30 to 11.03 mSv. The organ-based TCM and bismuth shielding produced similar dose reduction to the breast.
Conclusion: Our study demonstrated that different CTPA clinical protocols determined by scanner capability and patient habitus may result in wide variations of radiation dose to the breast. The V/Q scan is the recommended imaging method when DSCT is not available.
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