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Radiation dose reduction at a price: the effectiveness of a male gonadal shield during helical CT scans
© Dauer et al; licensee BioMed Central Ltd. 2007
Received: 29 September 2006
Accepted: 16 March 2007
Published: 16 March 2007
It is estimated that 60 million computed tomography (CT) scans were performed during 2006, with approximately 11% of those performed on children age 0–15 years. Various types of gonadal shielding have been evaluated for reducing exposure to the gonads. The purpose of this study was to quantify the radiation dose reduction to the gonads and its effect on image quality when a wrap-around male pediatric gonad shield was used during CT scanning. This information is obtained to assist the attending radiologist in the decision to utilize such male gonadal shields in pediatric imaging practice.
The dose reduction to the gonads was measured for both direct radiation and for indirect scattered radiation from the abdomen. A 6 cm3 ion chamber (Model 10X5-6, Radcal Corporation, Monrovia, CA) was placed on a Humanoid real bone pelvic phantom at a position of the male gonads. When exposure measurements with shielding were made, a 1 mm lead wrap-around gonadal shield was placed around the ion chamber sensitive volume.
The use of the shields reduced scatter dose to the gonads by a factor of about 2 with no appreciable loss of image quality. The shields reduced the direct beam dose by a factor of about 35 at the expense of extremely poor CT image quality due to severe streak artifacts.
Images in the direct exposure case are not useful due to these severe artifacts and the difficulties in positioning these shields on patients in the scatter exposure case may not be warranted by the small absolute reduction in scatter dose unless it is expected that the patient will be subjected to numerous future CT scans.
The use of computed tomography (CT) scanning has increased rapidly since its introduction in the early 1970s. During the 1990s CT usage almost doubled, representing about 11% of radiology procedures in 1999 . These values are consistent with a United States estimated rate for CT of 91 per 1000 population through the year 2000 . In 1999, about 11% of all CT scans were performed on children age 0–15 years . It is expected that the use of the modality will increase as the number of detectors and the clinical utility of CT is increased. It has been estimated that the number of CT scans performed annually has steadily increased in the U.S. from 2.8 million in 1981  to 20 million in 1995  and 60 million in 2006 , a number that seems destined to grow substantially. When using different sized acrylic phantoms to represent a range of pediatric and adult sizes undergoing CT with a typical 120 kVp x-ray beam, doses to the adult body range from 15–35 mGy while doses to the pediatric body are higher at 29–68 mGy using adult technique factors (milliampere-seconds). Similarly measured CT doses to the adult head range from 60–115 mGy while doses to the pediatric head are about 30% higher at 78–152 mGy using adult technique factors . Also, when you have similar techniques, the effective doses are substantially higher in children by a factor of about 2 to 4 .
Simple dose reduction methods that do not impair diagnostic image quality should be considered for clinical use  in an effort to reduce risks of induced cancers and other effects . Various authors have suggested that pediatric CT doses could be reduced by 30–50% or, more relative to adult doses, primarily by reducing the milliampere-seconds utilized, with no loss of diagnostic accuracy [5, 9–14]. In a further attempt at reducing exposures to specific areas of the pediatric body, physicians are increasingly considering the use of shielding devices, including specially designed gonadal shielding for male testes. CT represents a shielding challenge because of the confounding dose from both the primary x-ray beam and the significant scatter component in the body during the multi-slice scanning.
The current approved recommendations by the International Commission on Radiological Protection suggests that the weighting factor for the male gonads is 0.20 based on the radiation sensitivity of the gonads due to the risk of mutagenesis , with the dose to the gonads therefore contributing 20% of the effective whole-body dose (note that the most recent draft recommendations suggest a reduced weighting factor of 0.08 for the gonads ). Various shielding designs have been developed over the years to reduce gonadal doses including lead blankets, bismuth shielding, clam-shell style male testicular shields, and flexible shields.
The goal of our phantom study was obtain information to assist the attending radiologist in the decision to utilize such male gonadal shields in pediatric imaging practice. Although previous studies have evaluated various male gonad shielding designs, we set out to measure the effect of a specific design made up of a 1 mm lead equivalent, flexible, velcro-held, wrap-around pediatric male gonad shield (Flexible gonad protector, Dr. Goos-Suprema, Heidelberg, Germany) on the testicular radiation exposure from both the primary beam and the scatter component during abdominal and pelvic helical CT scans using techniques utilized at our institution. In addition, the effect of the presence of the shield on the CT image was also evaluated.
CT technique factors utilized in this study
Adult – Helical
Time per rotation (s)
Scan Field of View
Z-axis collimation (mm)
Table speed (mm/rot)
Reconstructed Scan Width (mm)
In the second trial, a pelvis scan was performed to examine the effect of shielding on direct radiation (both primary and exit). In this trial, the pelvis of the phantom was scanned using the same routine abdominopelvic examination protocol (Table 1) in a craniocaudal direction from the area just above the bottom edge of the symphysis to the upper thigh. The resulting exposure was measured both with and without the gonadal shield in place. For this trial, measurements were also repeated five times for the large shield and one time each for the small and medium shields.
For both trials, the radiation exposures to the testicular region with and without the wrap-around gonadal shielding were compared using the Student's t test. Statistical significance was set at a p value of less than 0.05.
During both trials, representative CT images were obtained in order to evaluate image quality on the basis of noise measurements and visual inspection of image artifacts with and without the gonadal shield in place.
Measured ion chamber readings (mR) representing gonadal exposure from an abdominal CT scan
Large Shield (650 cm 3 )
Medium Shield (450 cm 3 )
Small Shield (150 cm 3 )
Average +/- std.dev.
68.6 +/- 0.9
29.1 +/- 0.5
Measured ion chamber readings (mR) representing gonadal exposure from a pelvic CT scan
Large Shield (650 cm 3 )
Medium Shield (450 cm 3 )
Small Shield (150 cm 3 )
Average +/- std.dev.
4806 +/- 8.9
137.2 +/- 1.9
For the abdominal scans without gonadal shielding, the scatter exposure component to the gonads represented about 1.5% of the exposure to the gonads during a direct pelvic scan without gonadal shielding. For the abdominal scan, the large wrap-around shields appear to reduce the scatter exposure to the gonads by about 58%. For the direct pelvis scan, the exposure to the gonads was much higher, at 4820+/-14 mR, and the large wrap-around shields provided a more substantial shielding effect, reducing the direct beam exposure to the gonads by about 97%.
Comparison of literature reports and present study for scattered dose reduction with the use of gonadal shields during abdominal CT scans (with the testes not in the direct beam)
Testicular Dose (mGy)
Hidajat et al. 1996 
Phantom, 1 mm capsule
Single-slice sequential, 10 mm slice, 250 mAs/slice, 120 kV
Price et al. 1995 
Phantom, 1 mm wrap-around lead rubber
Single-slice spiral, 10 mm slice, 220 mA, 120 kV
Hohl et al. 2005 
Patient, 1 mm capsule
16-slice spiral, 16 × 1.5 mm collimation,150 mAseff,120 kV
Phantom, 1 mm wrap-around canvas
16-slice spiral, 16 × 1.25 mm collimation 194 mAseff, 120 kV
Image quality does not appear to be significantly affected when the scanned area is well outside of the gonadal shield location as was the case of the abdominal scan (Figure 4). Image quality is significantly reduced when the shield is located within the scan volume itself as was the case of the pelvic scan (Figure 5). The severe streak artifacts, caused by the presence of lead in the shield, render the image diagnostically unusable for most CT studies . Therefore, an understanding of patient positioning and shielding usage is necessary. Although performed for general radiology applications and not for CT directly, a number of studies have shown that useful dose reduction tools such as simple shields are not always used correctly, resulting in inadequate coverage of reproductive organs because the shield was not positioned correctly, or inappropriately shaped or sized devices were utilized [23–25].
It is important to note that while gonadal shields may help reduce the scattered exposure component, there are other simple techniques that can be explored to reduce overall radiation exposure to pediatric patients. Geleijns et al. suggest that adjusting techniques, such as reducing tube current, can achieve an equal dose reduction while yielding better image quality compared with the use of shielding . In a jointly issued guideline, the National Cancer Institute and the Society for Pediatric Radiology suggest the following reduction techniques for pediatric patients : (1) perform only necessary CT examinations; (2) adjust exposure parameters for pediatric CT based on child size, region scanned, organ systems scanned, and scan resolution; and (3) to minimize the CT examinations that use multiple scans obtained during different phases of contrast enhancement (multiphase examinations) especially for body (chest and abdomen) imaging. The US Food and Drug Administration has also released recommendations for reducing pediatric CT doses that include: (1) optimizing CT settings; (2) reducing the number of multiple scans with contrast material; and (3) eliminating inappropriate referrals for CT.
A Humanoid phantom and a 6 cm3 ion chamber can be very useful when performing shielding evaluation studies for CT scanning. The 1 mm wrap-around lead design for the gonadal shields reduced the already low scatter exposure to the testes by a factor of about only 2 with no appreciable loss of image quality. The shields reduced the direct beam exposure by a factor of about 35 at the expense of extremely poor image quality due to severe streak artifacts. Images in the direct exposure case are not useful due to these severe artifacts and the difficulties in positioning these shields on patients in the scatter exposure case may not be warranted by the small absolute reduction in scatter dose unless it is expected that the patient will be subjected to numerous future CT scans.
The authors wish to thank the MSKCC Radiology Department for providing us research time on the CT scanner.
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