| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1 Departments of Radiology and Pediatrics, Cincinnati Children's Hospital
Medical Center and University of Cincinnati College of Medicine, 3333 Burnet
Ave., Cincinnati, OH 45229-3039.
2 Department of Radiology, Box 3808, Duke University Medical Center, Durham, NC
27710.
3 Computed Imaging Reference Systems, Inc., Norfolk, VA 23513.
4 Radiologia Pediatrica, Hospital Materno-Infantil Vall d'He, pg. Vall d'Hebron
119-129, E-08-35, Barcelona, Spain.
Received June 4, 2002;
accepted after revision July 24, 2002.
Address correspondence to L. F. Donnelly.
Abstract
 Top Abstract IntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
SUBJECTS AND METHODS. Fifty consecutive MDCT examinations (chest, 29; abdomen, 21) of female pediatric patients (mean age, 9 years; range, 2 months-18 years) were performed with a 2-ply (1.7 g of bismuth per square centimeter) bismuth shield (three sizes to accommodate patients of varying sizes) overlying the patient's breasts. MDCT images were evaluated for a perceptible difference in image quality in the lungs at the anatomic level under the shield as compared with nonshielded lung and whether the images were of diagnostic quality. In addition, 2-mm regions of interest were placed in the peripheral anterior and posterior portions of each lung in shielded and nonshielded areas, and noise (standard deviation in Hounsfield units) was measured in the regions. Differences among the regions in noise were compared for shielded versus nonshielded areas (paired t test). To measure differences in actual dose, we also evaluated the breast shield with an infant anthropomorphic phantom using thermoluminescent detectors in the breast tissue. The phantom was imaged with and without the breast shield using identical MDCT parameters.
RESULTS. All MDCT scans of patients were of diagnostic quality with no perceptible difference in image quality in shielded versus nonshielded lung. We found no statistically significant difference in noise between the shielded and nonshielded lung regions of interest (shielded: mean noise, 17.3 H; nonshielded: mean noise, 18.8 H; p = 0.5180). Phantom measurements revealed a 29% reduction in radiation dose to the breast when a medium-dose MDCT protocol was used.
CONCLUSION. Bismuth in-plane breast shielding for pediatric MDCT decreased radiation dose to the breast without qualitative or quantitative changes in image quality.
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
Breast tissue exposed to radiation from CT of the chest or abdomen is an area of particular concern in girls. Increased incidence of breast cancers has been shown in populations exposed to radiation doses similar to those received from CT scans [1, 14,15,16,17,18]. The younger the patient is when exposed to radiation, the higher the risk of carcinogenesis [1, 14,15,16,17,18]. One technique in which the radiation dose to the breast can be reduced is the use of in-plane breast shielding [14]. In-plane shielding is different than conventional shielding for radiographic examinations [14]. With conventional shielding, the purpose is to completely obstruct radiation exposure to a certain area. With in-plane shielding, the X-ray beam is partially blocked to reduce the dose to the underlying tissue while allowing enough X-ray beam to pass to be able to generate a diagnostic CT image. Currently, in-plane breast shields designed for adults are commercially available (AttenuRad CT Radioprotective Brassiere; F & L Medical Products, Vandergrift, PA), but these shields are not in widespread use in the United States. Little data about the use of in-plane breast shields in pediatric patients have been published. The purpose of this investigation was to evaluate the amount of dose reduction and the effect on image quality of using a bismuth in-plane breast shield when performing MDCT of the chest and abdomen in female pediatric patients.
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
Breast shields were constructed from bismuthcoated latex sheets (F & L Medical Products). Two sheets of the bismuth-coated latex (total for shield: 2-ply; density, 1.7 g of bismuth per square centimeter) were used to construct the breast shields. The sheets of latex were placed over a 1-cm-thick foam pad (Fig. 1). The foam rubber was used to give the shield more substance for positioning, to lift the bismuth latex away from the chest wall in an attempt to decrease radiation scatter from entering tissue, and to decrease the potential of artifacts. The foam and latex were then wrapped in protective tape, and the superior side of the breast shield was clearly marked to reduce the likelihood of the shield being placed upside down. Three sizes of shields were constructed to accommodate pediatric patients who ranged in age from 2 months to 18 years (mean, 9 years). The dimensions of the three shields were 12 x 4 cm, 30 x 7 cm, and 47 x 15 cm. Before each MDCT scan, breast shields were placed exterior to the subject's garments (Fig. 2A,2B,2C) and interior to the thoracic immobilization straps.
|
|
|
|
Data from the first 50 consecutive female patients to undergo MDCT of the chest or abdomen with breast shields in place were reviewed. This group included 29 subjects who underwent MDCT of the chest and 21 subjects who underwent MDCT of the abdomen. All MDCT scans were obtained for clinical indications.
Scans were acquired on an MDCT scanner (LightSpeed; General Electric Medical Systems, Milwaukee, WI). The imaging parameters included weight-based tube current (range, 30-150 mA) [2], a slice thickness of 5 mm, a 0.8-sec gantry rotation, a table speed of 15 mm per rotation, and 120 kVp.
All MDCT examinations were reviewed by a pediatric radiologist for qualitative differences in image appearance related to the presence or absence of the in-plane breast shields. Whether the lungs were clear and whether nodular opacities, airspace disease, atelectasis, or other abnormalities were present in the lungs were noted. MDCT images were evaluated for the presence or absence of perceptible differences in image quality when comparing the lungs at the anatomic level under the in-plane shields as compared with areas of lung not shielded (Fig. 3A,3B). The MDCT images were also judged to either be or not be of diagnostic quality.
|
|
For the MDCT examinations of the chest, the lung superior to the breast shields was typically used for the nonshielded lung. For the MDCT examinations of the abdomen, the visualized non-shielded lung was typically inferior to the position of the breast shield. In no patients were additional images obtained for the purpose of the study. For the MDCT examinations of the chest, patients were imaged from the cervicothoracic junction through the most inferior aspect of the lungs. For the MDCT examinations of the abdomen, the patients were imaged from above the diaphragm to the iliac crest or the pubic symphysis, depending on whether the pelvis was also imaged.
All MDCT images were also evaluated for quantitative differences in image noise related to the presence or absence of in-plane breast shields. Regions of interest ranging from 2 to 3 mm were placed in areas of clear lung, in areas with no overlying pulmonary vessels, and in the peripheral portions of lung (Fig. 4). These regions of interest were placed in anterior and posterior lung and in both shielded and nonshielded areas. Noise, recorded as standard deviation in Hounsfield units, was measured in each of these regions. Noise for all regions was calculated by averaging the noise of the left anterior, right anterior, left posterior, and right posterior regions. Noise for the anterior region was calculated by averaging the noise of the left anterior and right anterior regions. Noise for the posterior region was calculated by averaging the noise of the left posterior and right posterior regions.
|
A paired t test was performed to determine whether the noise for all regions differed significantly for shielded versus nonshielded lungs. A second paired t test was performed using only the data for the shielded lungs to determine whether the noise of anterior versus posterior regions differed significantly.
To determine the radiation dose, we imaged an anthropomorphic dosimetric phantom (Newborn model ATOM 703; CIRS, Norfolk, VA) into which two calibrated thermoluminescent dosimeters (3 x 3 x 1 mm, Harshaw LiF TLD-100; Saint-Gobain Industrial Ceramics, Solon, OH) were placed to measure the dose to individual organs. The doses to individual organs were determined using the average dose of two thermoluminescent dosimeters chips; the background was subtracted using unexposed control chips. Organs into which thermoluminescent dosimeters were placed and recorded for the purposes of this study included breast and lung.
MDCT parameters for imaging the chest of an infant were consistent with those guidelines for single-detector CT [2] and consisted of a 3.75-mm detector configuration, 11.25 mm per rotation gantry speed (pitch of 0.75, HQ mode), 0.8-sec gantry rotation time, 50 mA (= 40 mAs), and 120 kVp. The phantom was imaged using the same protocol with and without the bismuth breast shield.
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
|
|
|
|
The mean noise for all regions in the shielded lung was 17.32 versus 18.81 H for the areas not underlying the breast shields. This difference in noise between shielded and nonshielded areas was not statistically significant (p = 0.5180). The mean noise value for the anterior and posterior regions in the shielded lung was 17.14 and 17.50 H, respectively. The difference in these noise values was not statistically significant (p = 0.5873).
The radiation doses with and without the shield, respectively, were 1.4 versus 1.5 rad (0.014 vs 0.015 Gy) for lung, and 1.2 versus 1.7 rad (0.012 vs 0.017 Gy) for breast. These results indicate the shield enabled a 6.7% decrease in radiation dose to the lung and a 29% decrease to the breast. Error bars for the thermoluminescent dosimeter measurements are typically regarded as 20%.
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
Radiation exposure is the major limitation to the use of CT. Although CT consists of only 11% of radiologic examinations, estimates suggest that CT is responsible for 67% of the radiation dose from medical imaging to the population [19]. Evidence indicates that the incidence of cancer is increased in patients who are exposed to the amount of radiation similar to that received from a CT examination performed with the parameters used in current practice [1, 17, 18]. Although minimizing radiation exposure as much as possible is important in all patients, it is particularly important in pediatric patients. The risk of carcinogenesis from radiation exposure has been shown to dramatically increase with younger age at the time of exposure [1, 17, 18]. Infants are up to 10 times more susceptible to carcinogenesis from radiation exposure than are adults [1, 17, 18]. In addition, girls are more susceptible to carcinogenesis from radiation exposure in general than are boys [1].
For these reasons, all techniques that can be used to minimize the dose associated with CT while maintaining diagnostic imaging quality should be implemented so that the risk of carcinogenesis in children is minimized. These techniques include using a weight-based table to determine tube current, increasing table speed or pitch, increasing the speed of gantry rotation, the judicious use of CT (including using other imaging techniques when possible), and avoiding the use of unenhanced CT when contrast-enhanced CT is performed [2, 9,10,11,12,13]. Implementing these dose-reducing measures is even more pertinent with the increased use of MDCT. For example, simply translating single-detector CT parameters to those used for MDCT can result in a 67% increase in dose that children receive [21].
The association between low-dose radiation exposure to breast tissue and the development of breast cancer has been well described [1, 14,15,16,17,18, 22,23,24]. The radiation exposure to the breast from a CT examination performed with the parameters set for an adult is estimated to be between 2.0 and 3.5 rad (0.020-0.035 Gy). This dose is the equivalent to that of approximately 10 mammograms or 100 chest radiographs [22,23,24,25,26,27]. The delivery of 1 rad (0.01 Gy)—a smaller dose than that associated with CT performed using a technique tailored for adults—to a woman younger than 35 years is estimated to increase her lifetime risk of breast cancer by 13.6% [14, 28, 29]. This risk is thought to be of increased magnitude with younger age, with the highest risk during infancy [1].
In-plane shielding is an additional technique that can be used to reduce radiation dose to radiosensitive organs, such as the breast. The use of an in-plane bismuth shield for dose reduction to the breast during CT has been described in adult subjects [14]. These authors reported a decrease in dose of 57% to the breast tissue of adults when this system was used. With in-plane shielding, the X-ray beam is partially blocked to reduce the dose to the underlying surface tissue while allowing enough X-ray beams to pass to generate a diagnostic CT image. Using in-plane shielding rather than adjusting CT parameters, such as tube current, to lower levels has advantages. For example, when using in-plane shields, only the images that are obtained at the level of the radiosensitive organ are affected, rather than the entire anatomic area of interest. Also, because the breast shields are only on the anterior portion of the chest, the lateral portions of the 360° rotation are not affected by the shields and contribute to image formation of the lungs and mediastinum without attenuation from the shields. Moreover, in-plane shielding can be used to protect other radiosensitive organs such as the thyroid.
With the implementation of our in-plane breast shield program, radiation exposure to the breast tissue of infants was reduced by 29% without any perceptible change in image quality. In addition, no quantitative change was detected in the amount of noise in the regions covered by the breast shield versus those not covered. The radiation dose to the lung was less affected by the presence of the shields with only a 6.7% decrease in radiation dose. The dose reduction to the lung is most likely smaller because the lung is a deep structure and radiation can reach the lung from all portions of the 360° arc of the beam.
The breast shields used in our current practice differ from those described by Hopper et al. [14] in several ways. First, the breast shields we use are constructed with a 1-cm foam pad placed between the bismuth latex and the patient. The purpose of this foam is multifold. First, the foam gives the shields more substance and durability, making them easier to work with. Second, the foam pad elevates the bismuth shield away from the patient's tissues. This construction was intended to decrease the amount of scatter radiation entering the patient to both further decrease the radiation exposure to the breast and decrease the amount of artifact or noise. Hopper et al. described artifacts identified over the breast tissue but not the lung. On MDCT scans obtained with the foam pad in place, we saw no artifacts in the breast tissue or lung. Physical differences may need to be considered when designing shields for adult women as compared with children whose breast tissue is smaller in volume.
The second difference between the breast shields used in this study and those used by Hopper et al. [14] is the amount of bismuth used. Hopper et al. evaluated bismuth shields that were 1-, 2-, 3-, and 4-ply in thickness (each ply = 0.85 g of bismuth per square centimeter). In that study, the dose reduction of 57% was achieved with the 4-ply system. When we designed our clinical breast shield program, we elected to start conservatively with a 2-ply system. We thought that maintaining image quality rather than compromising image quality for further dose reduction was more prudent. The 29% dose reduction achieved with our 2-ply system is in-line with the 28% reduction seen by Hopper et al. when testing a 2-ply system. The current commercially available shields constructed for adults are 4-ply (AttenuRad CT Radioprotective Brassiere; F & L Medical Products). Now that we have shown that a 2-ply system can be used without image degradation in the pediatric population, further investigation into the potential use of a 4-ply system may be warranted.
In conclusion, we found that radiation exposure to the breast could be reduced by 29% without compromising image quality using a 2-ply in-plane breast shield system. In-plane breast shielding offers an additional method of minimizing dose to female pediatric patients undergoing MDCT. Further study is warranted to determine the optimal breast shield construction.
|
TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  D. Honnef, J. E. Wildberger, G. Haras, C. Hohl, G. Staatz, R. W. Gunther, and A. H. Mahnken Prospective Evaluation of Image Quality with Use of a Patient Image Gallery for Dose Reduction in Pediatric 16-MDCT Am. J. Roentgenol., February 1, 2008; 190(2): 467 - 473. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
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 Am. J. Roentgenol., January 1, 2008; 190(1): W54 - W61. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E V Kennedy, G R Iball, and D S Brettle Investigation into the effects of lead shielding for fetal dose reduction in CT pulmonary angiography Br. J. Radiol., August 1, 2007; 80(956): 631 - 638. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Warren-Forward, P. Cardew, B. Smith, L. Clack, K. McWhirter, S. Johnson, and K. Wessel A COMPARISON OF DOSE SAVINGS OF LEAD AND LIGHTWEIGHT APRONS FOR SHIELDING OF 99m-TECHNETIUM RADIATION Radiat Prot Dosimetry, May 24, 2007; (2007) ncm176v1. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. T. Yoshizumi, P. C. Goodman, D. P. Frush, G. Nguyen, G. Toncheva, M. Sarder, and L. Barnes Validation of Metal Oxide Semiconductor Field Effect Transistor Technology for Organ Dose Assessment During CT: Comparison with Thermoluminescent Dosimetry Am. J. Roentgenol., May 1, 2007; 188(5): 1332 - 1336. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Schueller-Weidekamm, C. M. Schaefer-Prokop, M. Weber, C. J. Herold, and M. Prokop CT Angiography of Pulmonary Arteries to Detect Pulmonary Embolism: Improvement of Vascular Enhancement with Low Kilovoltage Settings Radiology, December 1, 2006; 241(3): 899 - 907. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. M. Hurwitz, T. T. Yoshizumi, R. E. Reiman, E. K. Paulson, D. P. Frush, G. T. Nguyen, G. I. Toncheva, and P. C. Goodman Radiation dose to the female breast from 16-MDCT body protocols. Am. J. Roentgenol., June 1, 2006; 186(6): 1718 - 1722. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. S. Parker, F. K. Hui, M. A. Camacho, J. K. Chung, D. W. Broga, and N. N. Sethi Female Breast Radiation Exposure During CT Pulmonary Angiography Am. J. Roentgenol., November 1, 2005; 185(5): 1228 - 1233. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M A Lewis and S Edyvean Patient dose reduction in CT Br. J. Radiol., October 1, 2005; 78(934): 880 - 883. [Full Text] [PDF]
|
|
|
|
|
|
L. F. Donnelly Reducing Radiation Dose Associated with Pediatric CT by Decreasing Unnecessary Examinations Am. J. Roentgenol., February 1, 2005; 184(2): 655 - 657. [Full Text] [PDF]
|
|
|
|
|
|
C. Hohl, A. H. Mahnken, E. Klotz, M. Das, A. Stargardt, G. Muhlenbruch, T. Schmidt, R. W. Gunther, and J. E. Wildberger Radiation Dose Reduction to the Male Gonads During MDCT: The Effectiveness of a Lead Shield Am. J. Roentgenol., January 1, 2005; 184(1): 128 - 130. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. P. Frush, L. F. Donnelly, and N. S. Rosen Computed Tomography and Radiation Risks: What Pediatric Health Care Providers Should Know Pediatrics, October 1, 2003; 112(4): 951 - 957. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. F. Donnelly, J. Lucaya, V. Ozelame, D. P. Frush, P. J. Strouse, T. E. Sumner, and H. J. Paltiel CT Findings and Temporal Course of Persistent Pulmonary Interstitial Emphysema in Neonates: A Multiinstitutional Study Am. J. Roentgenol., April 1, 2003; 180(4): 1129 - 1133. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
