Shane Foley BSC, Presenter: Nothing to Disclose

Mark McEntee, Abstract Co-Author: Nothing to Disclose

Patrick C. Brennan PhD, Abstract Co-Author: Nothing to Disclose

Louise Ann Rainford PhD, Abstract Co-Author: Nothing to Disclose

Jonathan Dodd MD, Abstract Co-Author: Nothing to Disclose

To use TLDs to calculate the absorbed radiation dose to the female breast tissue during 64 slice cardiac CT, using both patients and an anthropomorphic phantom.

In this institutional review board approved, HIPAA-compliant study, 16 female patients (mean age 60.7 years ± 10.6 (range 43-79 years), prospectively underwent 64-slice coronary CT for evaluation of chest pain. For all studies, sets of three thermoluminescent dosimeters (TLDs) 100s were placed on each quadrant and the areolar region of both breasts. Imaging was performed on a 64 slice scanner (Siemens Sensation 64) with cardiac CT scan parameters (120kVp, 800 effective mAs, with ECG-tube current modulation, 64 mm × 0.6 mm collimation, gantry rotation time 330 ms, pitch 0.2, image reconstruction with a slice thickness of 0.6mm and a slice overlap of 0.3mm.). Radiation doses were recorded. An anthropomorphic phantom was subsequently scanned with identical scan parameters but with TLDs placed on the surface and also in cavities within the breast at depths of 2.5, 5 and 7.5cm to directly measure absorbed breast radiation dose.

Radiation dose at the surface of the breast phantom averaged 31mGy ± 4, with the four quadrants recording similar doses (mean: 33mGy ± 1.6). At increasing depths the TLDs recorded increasing mean radiation doses of 33, 36 and 39mGy at depths of 2.5, 5 and 7.5cm. The patient study demonstrated an average dose of 24mGy ± 9 with the inferior quadrants and the areolar region recording higher doses (mean: 30.9mGy ) while the upper quadrants averaged 14.4mGy.

Average absorbed breast radiation dose to the female breast phantom is up to 39mGy during 64 slice cardiac CT, with increasing doses recorded with increasing tissue depths. Surface TLD measurements may therefore underestimate the absorbed dose to the breast by up to 24% depending on breast size. The patient study also revealed that the upper quadrants may receive smaller doses due to their patient specific location which may lie outside of the limited scan range used in cardiac scanning.

Awareness of the doses associated with new scanning techniques is emphasised as is the need for further optimisation.

Foley, S, McEntee, M, Brennan, P, Rainford, L, Dodd, J, TLD Measurement of Absorbed Radiation Dose to the Female Breast during 64 Slice Cardiac CT.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9010101.html