Objectives. To compare the effectiveness of the bismuth breast shield and partial CT scan in reducing entrance skin dose and to evaluate the effect of the breast shield on image quality (IQ). Methods. Nanodots were placed on an adult anthropomorphic phantom. Standard chest CT, CT with shield, and partial CT were performed. Nanodot readings and effective doses were recorded. 50 patients with chest CTs obtained both with and without breast shields were reviewed. IQ was evaluated by two radiologists and by measuring Hounsfield units (HUs) and standard deviation (SD) of HU in anterior subcutaneous region. Results. Breast shield and the partial CT scans reduced radiation to the anterior chest by 38% and 16%, respectively. Partial CT increased dose to the posterior chest by 37% and effective dose by 8%. Change in IQ in shield CT was observed in the anterior chest wall. Significant change in IQ was observed in 5/50 cases. The shield caused an increase of 20？HU ( ) and a 1.86 reduction in SD of HU ( ) in the anterior compared to posterior subcutaneous regions. Summary. Bismuth breast shield is more effective than the partial CT in reducing entrance skin dose while maintaining image quality. 1. Introduction Computed tomography (CT) has emerged as an important diagnostic tool in clinical medicine. Its use has grown exponentially over the years, rising from 3 million in 1980 to 67 million in 2006, an equivalent of a 600% increase from 1980 to 2006 [1]. This significant rise in frequency also brings into question the level of radiation exposure to patients. The potential carcinogenic effect of this increased radiation dose on radiosensitive tissues has fostered much concern recently [2] and breast tissue exposure from chest CT is an area of particular concern in females. In 2008, the International Commission of Radiation Protection (ICRP) increased the tissue weighting factor for the breast from 0.05 to 0.12 [3]. The radiation exposure to the breast from a chest CT is estimated to be 2.0–3.5 rad, which is equivalent to 10 mammograms or 100 chest radiographs [4]. These doses far exceed the American College of Radiology recommendation of 0.3？rad or less for a standard 2-view mammography. The delivery of 1？rad to a woman younger than age 35 years old is estimated to increase her lifetime risk of breast cancer by 13.6% [4–7]. Due to this risk, several techniques have been developed to reduce the radiation exposure to the breast during a chest CT. The in-plane bismuth breast shield has been shown to be effective at reducing radiation dose to the breast. An early study
References
[1]
F. A. Mettler Jr., M. Bhargavan, K. Faulkner et al., “Radiologic and nuclear medicine studies in the United States and worldwide: Frequency, radiation dose, and comparison with other radiation sources—1950–2007,” Radiology, vol. 253, no. 2, pp. 520–531, 2009.
[2]
D. J. Brenner and E. J. Hall, “Computed tomography—an increasing source of radiation exposure,” New England Journal of Medicine, vol. 357, no. 22, pp. 2277–2284, 2007.
[3]
A. D. Wrixon, “New ICRP recommendations,” Journal of Radiological Protection, vol. 28, no. 2, pp. 161–168, 2008.
[4]
K. D. Hopper, S. H. King, M. E. Lobell, T. R. TenHave, and J. S. Weaver, “The breast: In-plane x-ray protection during diagnostic thoracic CT—shielding with bismuth radioprotective garments,” Radiology, vol. 205, no. 3, pp. 853–858, 1997.
[5]
L. M. Hurwitz, T. T. Yoshizumi, R. E. Reiman et al., “Radiation dose to the female breast from 16-MDCT body protocols,” American Journal of Roentgenology, vol. 186, no. 6, pp. 1718–1722, 2006.
[6]
B. Liu, M. Goodsitt, and H. P. Chan, “Normalized average glandular dose in magnification mammography,” Radiology, vol. 197, no. 1, pp. 27–32, 1995.
[7]
C. H. McCollough and H. H. Liu, “Breast dose during electron-beam CT: measurement with film dosimetry,” Radiology, vol. 196, no. 1, pp. 153–157, 1995.
[8]
P. Catuzzo, S. Aimonetto, G. Fanelli et al., “Dose reduction in multislice CT by means of bismuth shields: results of in vivo measurements and computed evaluation,” Radiologia Medica, vol. 115, no. 1, pp. 152–169, 2010.
[9]
P. Colombo, G. Pedroli, M. Nicoloso, S. Re, L. Valvassori, and A. Vanzulli, “Evaluation of the efficacy of a bismuth shield during CT examinations,” Radiologia Medica, vol. 108, no. 5-6, pp. 560–568, 2004.
[10]
C. Coursey, D. P. Frush, T. Yoshizumi, G. Toncheva, G. Nguyen, and S. B. Greenberg, “Pediatric chest MDCT using tube current modulation: effect on radiation dose with breast shielding.,” American Journal of Roentgenology, vol. 190, no. 1, pp. W54–W61, 2008.
[11]
B. L. Fricke, L. F. Donnelly, D. P. Frush et al., “In-plane bismuth breast shields for pediatric CT: effects on radiation dose and image quality using experimental and clinical data,” American Journal of Roentgenology, vol. 180, no. 2, pp. 407–411, 2003.
[12]
C. Hohl, J. E. Wildberger, C. Sü？ et al., “Radiation dose reduction to breast and thyroid during MDCT: Effectiveness of an in-plane bismuth shield,” Acta Radiologica, vol. 47, no. 6, pp. 562–567, 2006.
[13]
M. H. Yilmaz, S. Albayram, D. Ya？ar et al., “Female breast radiation exposure during thorax multidetector computed tomography and the effectiveness of bismuth breast shield to reduce breast radiation dose,” Journal of Computer Assisted Tomography, vol. 31, no. 1, pp. 138–142, 2007.
[14]
S. V. Vollmar and W. A. Kalender, “Reduction of dose to the female breast in thoracic CT: a comparison of standard-protocol, bismuth-shielded, partial and tube-current-modulated CT examinations,” European Radiology, vol. 18, no. 8, pp. 1674–1682, 2008.
[15]
M. F. McNitt-Gray, “AAPM/RSNA physics tutorialfor residents: topics in CT. Radiation dose in CT,” Radiographics, vol. 22, no. 6, pp. 1541–1553, 2002.
