Dose Considerations. For iodinated contrast studies of the breast, we propose to initially perform a pre-contrast scan and 1 post-contrast scan. Exact timing of the post-contrast scans needs to be explored as part of this study. The average glandular dose to the breast volume per scan will be 4 mGy to 13 mGy per scan (+/-20%), depending on breast size and density or similar to the subject’s diagnostic mammogram. Thus, the dose for a full two-scan protocol will be ~ 8 to 26 mGy, or similar to two diagnostic mammography exams. By comparison, this dose is up to 2-3 times lower than multi-slice CT scans of the breast, which results in a CTDI100 ~12-18 mGy glandular dose/scan. In addition, these multi-slice CT scans radiate the entire thorax in addition to the breast at much higher photon energies (120 kVp compared to 49 kVp). The effective dose from a conventional chest CT scan is 7 mSv, which is equivalent to 2 years of natural background radiation [16]. The effective dose from a two-scan, single breast CE- CBBCT exam is from 0.1.2 mSv to 3.8 mSv, which is equivalent to approximately 4.6 months to 14.7 months of natural background radiation. This conversion is based on a breast tissue weighting factor of 0.15 per NRC 10CFR 20.1003 Definitions. Two scans are typically performed at ~30 seconds and 2 minutes after contrast injection. In addition, 3 mm thick slices are taken to scan the breast volume. At 0.8 sec/rotation and a pitch of 1, it takes ~40 seconds to cover ~150 mm distance to capture the full breast. Contrast enhancement can change significantly during this time. The CBBCT scan, however, takes only 10 seconds to scan a full breast volume thus capturing a volume “snapshot” of the contrast-enhanced tumors at that time.
