Greta Toncheva

University of Texas Medical School, Houston, Texas, United States

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Publications (60)147.1 Total impact

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    ABSTRACT: OBJECTIVE. The purpose of this study was threefold: to estimate the organ doses and effective doses (EDs) for seven neurovascular imaging protocols, to study the effect of beam collimation on ED, and to derive protocol-specific dose-area product (DAP)-to-ED conversion factors. MATERIALS AND METHODS. A cone-beam CT system was used to measure the organ doses for seven neurovascular imaging protocols. Two datasets were obtained: seven protocols without beam collimation (FOV, entire head) and four with beam collimation (FOV, from the base to the top of the skull). Measurements were performed on an adult male anthropomorphic phantom with 20 metal oxide semiconductor field-effect transistor (MOSFET) detectors placed in selected organs. The DAP values were recorded from the console. The EDs of five protocols were also estimated using Monte Carlo simulations software. The ED values were computed by multiplying measured organ doses to corresponding International Commission on Radiological Protection tissue-weighting factors. RESULTS. Without collimation, the EDs ranged from 0.16 to 1.6 mSv, and the DAP-to-ED conversion factors ranged from 0.035 to 0.076 mSv/Gy·cm(2). For the four protocols investigated with beam collimation, the ED was reduced by a factor of approximately 2, and the DAP-to-ED conversion factors were reduced by approximately 30%. For the five protocols also estimated with the Monte Carlo method, the estimated EDs were in agreement (< 20% deviation) with those determined by the MOSFET method. CONCLUSION. We have estimated ED for standard adult neuroimaging protocols in a 3D rotational angiography system. Our results provide a simple means of ED estimation using DAP console readings.
    American Journal of Roentgenology 05/2014; 202(5):1072-7. · 2.90 Impact Factor
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    ABSTRACT: The purpose of this study was three-fold: (1) to measure the transmission properties of various lead shielding materials, (2) to benchmark the accuracy of commercial film badge readings, and (3) to compare the accuracy of effective dose (ED) conversion factors (CF) of the U.S. Nuclear Regulatory Commission methods to the MOSFET method. The transmission properties of lead aprons and the accuracy of film badges were studied using an ion chamber and monitor. ED was determined using an adult male anthropomorphic phantom that was loaded with 20 diagnostic MOSFET detectors and scanned with a whole body CT protocol at 80, 100, and 120 kVp. One commercial film badge was placed at the collar and one at the waist. Individual organ doses and waist badge readings were corrected for lead apron attenuation. ED was computed using ICRP 103 tissue weighting factors, and ED CFs were calculated by taking the ratio of ED and badge reading. The measured single badge CFs were 0.01 (±14.9%), 0.02 (±9.49%), and 0.04 (±15.7%) for 80, 100, and 120 kVp, respectively. Current regulatory ED CF for the single badge method is 0.3; for the double-badge system, they are 0.04 (collar) and 1.5 (under lead apron at the waist). The double-badge system provides a better coefficient for the collar at 0.04; however, exposure readings under the apron are usually negligible to zero. Based on these findings, the authors recommend the use of ED CF of 0.01 for the single badge system from 80 kVp (effective energy 50.4 keV) data.
    Health physics 05/2014; 106(5):551-7. · 0.92 Impact Factor
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    ABSTRACT: OBJECTIVE. The purpose of this study was to measure the organ doses and estimate the effective dose for the standard brain perfusion CT protocol and erroneous protocols. MATERIALS AND METHODS. An anthropomorphic phantom with metal oxide semiconductor field effect transistor (MOSFET) detectors was scanned on a 64-MDCT scanner. Protocol 1 used a standard brain perfusion protocol with 80 kVp and fixed tube current of 200 mA. Protocol 2 used 120 kVp and fixed tube current of 200 mA. Protocol 3 used 120 kVp with automatic tube current modulation (noise index, 2.4; minimum, 100 mA; maximum, 520 mA). RESULTS. Compared with protocol 1, the effective dose was 2.8 times higher with protocol 2 and 7.8 times higher with protocol 3. For all protocols, the peak dose was highest in the skin, followed by the brain and calvarial marrow. Compared with protocol 1, the peak skin dose was 2.6 times higher with protocol 2 and 6.7 times higher with protocol 3. The peak skin dose for protocol 3 exceeded 3 Gy. The ocular lens received significant scatter radiation: 177 mGy for protocol 2 and 435 mGy for protocol 3, which were 4.6 and 11.3 times the dose for protocol 1, respectively. CONCLUSION. Compared with the standard protocol, erroneous protocols of increasing the tube potential from 80 kVp to 120 kVp will lead to a three- to fivefold increase in organ doses, and concurrent use of high peak kilovoltage with incorrectly programmed tube current modulation can increase dose to organs by 7- to 11-fold. Tube current modulation with a low noise index can lead to doses to the skin and ocular lens that are close to thresholds for tissue reactions.
    American Journal of Roentgenology 09/2013; · 2.90 Impact Factor
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    ABSTRACT: Efforts to decrease radiation exposure during pediatric high-resolution thoracic computed tomography (HRCT), while maintaining diagnostic image quality, are imperative. The objective of this investigation was to compare organ doses and scan performance for pediatric HRCT using volume, helical, and noncontiguous axial acquisitions. Thoracic organ doses were measured using 20 metal oxide semiconductor field-effect transistor dosimeters. Mean and median organ doses and scan durations were determined and compared for three acquisition modes in a 5-year-old anthropomorphic phantom using similar clinical pediatric scan parameters. Image noise was measured and compared in identical regions within the thorax. There was a significantly lower dose in lung (1.8 vs 2.7 mGy, P < .02) and thymus (2.3 vs 2.7 mGy, P < .02) between volume and noncontiguous axial modes and in lung (1.8 vs 2.3 mGy, P < .02), breast (1.8 vs 2.6 mGy, P < .02), and thymus (2.3 vs 2.4 mGy, P < .02) between volume and helical modes. There was a significantly lower median image noise for volume compared to helical and axial modes in lung (55.6 vs 79.3 and 70.7) and soft tissue (76.0 vs 111.3 and 89.9). Scan times for volume, helical, and noncontiguous axial acquisitions were 0.35, 3.9, and 24.5 seconds, respectively. Volumetric HRCT provides an opportunity for thoracic organ dose and image noise reduction, at significantly faster scanning speeds, which may benefit pediatric patients undergoing surveillance studies for diffuse lung disease.
    Academic radiology 09/2013; 20(9):1152-61. · 2.09 Impact Factor
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    ABSTRACT: PURPOSE: Computed tomography (CT) utilization over the last three decades has increased exponentially. CT is commonly used to evaluate many urologic conditions. Ionizing radiation exposure from medical imaging has been linked to the risk of developing malignancy. We measured the organ doses (OD) and calculated effective doses (ED) of different studies and determined if the dose length product (DLP) method is an accurate estimation of radiation exposure. MATERIAL AND METHODS: An anthropomorphic male phantom that has been validated for human organ dosimetry measurements was used to determine radiation doses. High sensitivity MOSFET dosimeters were placed at 20 organ locations to measure specific OD. For each study, the phantom was scanned three times using our institutional protocols. ODs were measured and the ED was calculated (EDMOSFET). The EDMOSFET were compared to calculated EDs (EDcal) derived from the DLP. RESULTS: The EDMOSFET for stone protocol CT, chest CT, CT abdomen and pelvis, CT urogram and renal cell carcinoma (RCC) protocol CT were 3.04 ± 0.34, 4.34 ± 0.27, 5.19 ± 0.64, 9.73 ± 0.71 and 11.42 ± 0.24 milliSievert (mSv), respectively. The EDcal for these studies were 3.33, 2.92, 5.84, 9.64 and 10.06 mSv, p=0.8478. CONCLUSIONS: Effective doses in different urologic CT studies vary considerably. Renal stone protocol CT is accompanied by the lowest dose while CT urogram and RCC protocol accumulate the highest EDs. EDcal derived from the DLP is a reasonable estimate of patient radiation exposure.
    The Journal of urology 06/2013; · 4.02 Impact Factor
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    ABSTRACT: Objective: To compare the effective doses (ED) associated with imaging modalities for follow-up of patients with urolithiasis, including stone protocol NCCT, KUB, IVP and digital tomosynthesis (DT). Methods: A validated Monte Carlo simulation-based software PCXMC 2.0 (STUK, Finland) designed for estimation of patient dose from medical x-ray exposures was used to determine the ED for KUB, IVP (KUB scout plus 3 tomographic images) and DT (2 scouts and 1 tomographic sweep). Simulations were performed using a 2D stationary field onto the corresponding body area of the built-in digital phantom, with actual kVp, mAs, and geometrical parameters of the protocols. The ED for NCCT was determined using an anthropomorphic male phantom which was placed prone on a 64-slice GE Healthcare VCT scanner. High sensitivity metal oxide semiconductor field effect transistors (MOSFET) dosimeters were placed at 20 organ locations and used to measure organ radiation doses. Results: The ED for a stone protocol NCCT was 3.04±0.34 mSv. The ED for a KUB was 0.63 mSv and 1.1 mSv for the additional tomographic film. The total ED for IVP was 3.93 mSv. The ED for digital tomosynthesis performed with two scouts and one sweep (60.0°) was 0.83 mSv. Conclusions: Among the different imaging modalities for follow-up of patients with urolithiasis, DT was associated with the least radiation exposure (0.83 mSv). This effective dose corresponds to a fifth of NCCT or IVP studies. Further studies are needed to demonstrate the sensitivity and specificity of DT for the follow-up of nephrolithiasis patients.
    Journal of endourology / Endourological Society 06/2013; · 1.75 Impact Factor
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    ABSTRACT: BACKGROUND: Advanced multidetector CT systems facilitate volumetric image acquisition, which offers theoretic dose savings over helical acquisition with shorter scan times. OBJECTIVE: Compare effective dose (ED), scan duration and image noise using 320- and 64-detector CT scanners in various acquisition modes for clinical chest, abdomen and pelvis protocols. MATERIALS AND METHODS: ED and scan durations were determined for 64-detector helical, 160-detector helical and volume modes under chest, abdomen and pelvis protocols on 320-detector CT with adaptive collimation and 64-detector helical mode on 64-detector CT without adaptive collimation in a phantom representing a 5-year-old child. Noise was measured as standard deviation of Hounsfield units. RESULTS: Compared to 64-detector helical CT, all acquisition modes on 320-detector CT resulted in lower ED and scan durations. Dose savings were greater for chest (27-46%) than abdomen/pelvis (18-28%) and chest/abdomen/pelvis imaging (8-14%). Noise was similar across scanning modes, although some protocols on 320-detector CT produced slightly higher noise. CONCLUSION: Dose savings can be achieved for chest, abdomen/pelvis and chest/abdomen/pelvis examinations on 320-detector CT compared to helical acquisition on 64-detector CT, with shorter scan durations. Although noise differences between some modes reached statistical significance, this is of doubtful diagnostic significance and will be studied further in a clinical setting.
    Pediatric Radiology 05/2013; · 1.57 Impact Factor
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    ABSTRACT: INTRODUCTION AND OBJECTIVE: Patients with recurrent nephrolithiasis are often evaluated and followed with computerized tomography (CT). Obesity is a risk factor for the development of nephrolithiasis. We evaluated the radiation dose from CT for obese and non-obese adults. MATERIALS AND METHODS: A validated, anthropomorphic male phantom was scanned according to our institutional protocol for evaluation of renal stones. The obese model consisted of the phantom wrapped in two Custom Fat Layers, which have been verified to have the same radiographic tissue density as fat. High sensitivity metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ locations in the phantoms to measure organ specific radiation doses. The non-obese and obese model have an approximate BMI of 24 kg/m2 and 30 kg/m2, respectively. Three runs of the renal stone protocol CT were performed on each phantom under automatic tube current modulation. Organ-specific absorbed doses were measured and the effective doses were calculated. RESULTS: For both models, the bone marrow received the highest dose, with the skin receiving the second highest dose. The mean effective dose for the non-obese model was 3.04 ± 0.34 milli- Sieverts (mSv), while the effective dose for the obese model was 10.22 ± 0.50 mSv, p<0.0001. CONCLUSIONS: The effective dose of stone protocol CT for obese patients is more than three-fold higher than the dose for a non-obese patient using automatic tube current modulation. The implication of this finding extends beyond the urologic stone population and adds to our understanding of radiation exposure from medical imaging.
    The Journal of urology 12/2012; · 4.02 Impact Factor
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    ABSTRACT: The purpose of this study is to determine patient dose estimates for clinical pediatric cardiac-gated CT angiography (CTA) protocols on a 320-MDCT volume scanner. Organ doses were measured using 20 metal oxide semiconductor field effect transistor (MOSFET) dosimeters. Radiation dose was estimated for volumetrically acquired clinical pediatric prospectively and retrospectively ECG-gated cardiac CTA protocols in 5-year-old and 1-year-old anthropomorphic phantoms on a 320-MDCT scanner. Simulated heart rates of 60 beats/min (5-year-old phantom) and 120 beats/min (1- and 5-year-old phantoms) were used. Effective doses (EDs) were calculated using average measured organ doses and International Commission on Radiological Protection 103 tissue-weighting factors. Dose-length product (DLP) was recorded for each examination and was used to develop dose conversion factors for pediatric cardiac examinations acquired with volume scan mode. DLP was also used to estimate ED according to recently published dose conversion factors for pediatric helical chest examinations. Repeated measures and paired Student t test analyses were performed. For the 5-year-old phantom, at 60 beats/min, EDs ranged from 1.2 mSv for a prospectively gated examination to 4.5 mSv for a retrospectively gated examination. For the 5-year-old phantom, at 120 beats/min, EDs ranged from 3.0 mSv for a prospectively gated examination to 4.9 mSv for a retrospectively gated examination. For the 1-year-old phantom, at 120 beats/min, EDs ranged from 2.7 mSv for a prospectively gated examination to 4.5 mSv for a retrospectively gated examination. EDs for 320-MDCT volumetrically acquired ECG-gated pediatric cardiac CTA are lower than those published for conventional 16- and 64-MDCT scanners.
    American Journal of Roentgenology 11/2012; 199(5):1129-35. · 2.90 Impact Factor
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    ABSTRACT: The purpose of this study was to assess the radiation dose distribution and image quality for organ-based dose modulation during adult thoracic MDCT. Organ doses were measured using an anthropomorphic adult female phantom containing 30 metal oxide semiconductor field-effect transistor detectors on a dual-source MDCT scanner with two protocols: standard tube current modulation thoracic CT and organ-based dose modulation using a 120° radial arc. Radiochromic film measured the relative axial dose. Noise was measured to evaluate image quality. Breast tissue location across the anterior aspect of the thorax was retrospectively assessed in 100 consecutive thoracic MDCT examinations. There was a 17-47% decrease (p = < 0.05) in anterior thoracic organ dose and a maximum 52% increase (p = < 0.05) in posterior thoracic organ dose using organ-based dose modulation compared with tube current modulation. Effective dose (SD) for tube current modulation and organ-based dose modulation were 5.25 ± 0.36 mSv and 4.42 ± 0.30 mSv, respectively. Radiochromic film analysis showed a 30% relative midline anterior-posterior gradient. There was no statistically significant difference in image noise. Adult female breast tissue was located within an average anterior angle of 155° (123-187°). Organ-based dose modulation CT using an anterior 120° arc can reduce the organ dose in the anterior aspect of the thorax with a compensatory organ dose increase posteriorly without impairment of image quality. Laterally located breast tissue will have higher organ doses than medially located breast tissue when using organ-based dose modulation. The benefit of this dose reduction must be clinically determined on the basis of the relationship of the irradiated organs to the location of the prescribed radial arc used in organ-based dose modulation.
    American Journal of Roentgenology 07/2012; 199(1):W65-73. · 2.90 Impact Factor
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    ABSTRACT: Purpose: The purpose of this study was three-fold: 1) to estimate the organ doses and effective dose (ED) for patients undergoing neuro 3D-imaging protocols, 2) to study the effect of beam collimation on ED, and 3) to derive protocol-specific DAP-to-ED conversion factors. Methods: A cone-beam CT system (Philips Allura Xper FD20/20) was used to measure the organ doses for seven neuro imaging protocols. Two data sets were obtained: seven protocols with uncollimated beam (FOV: entire head) and four with beam collimation (FOV: roughly from the base to the top of the skull). Measurements were performed on an adult male anthropomorphic phantom (CIRS, Norfolk, VA) with 20 MOSFET detectors (Best Medical Canada, Ottawa, Canada) placed in selected organs. The dose area product (DAP) values were recorded from console. The ED values were computed by multiplying measured organ doses to corresponding ICRP 103 tissue weighting factors. Results: For seven protocols with uncollimated setting, the EDs ranged from 0.16 mSv to 1.6 mSv, and the DAP-to-ED conversion factors range from 0.037 to 0.17 mSv/Gy/cm(2). For four protocols with beam collimation, the ED was reduced approximately by a factor of 2, and the DAP-to-ED conversion factors by approximately 30%. Conclusions: We have measured ED for standard adult neuro imaging protocols in a 3-D rotational angiography system. Our results provide a simple means of ED estimation using DAP values from console in the C-arm cone-beam CT system. Research was funded in part by Philips Healthcare, the Netherlands.
    Medical Physics 06/2012; 39(6):3620. · 2.91 Impact Factor
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    ABSTRACT: The purpose of this study was to assess the difference in absorbed organ dose and image quality for MDCT neck protocols using automatic tube current modulation alone compared with organ-based dose modulation and in-plane thyroid bismuth shielding. An anthropomorphic female phantom with metal oxide semiconductor field effect transistor (MOSFET) detectors was scanned on a 64-MDCT scanner. The protocols included a reference neck CT protocol using automatic tube current modulation and three modified protocols: organ-based dose modulation, automatic tube current modulation with thyroid shield, and organ-based dose modulation with thyroid shield. Image noise was evaluated quantitatively with the SD of the attenuation value, and subjectively by two neuroradiologists. Organ-based dose modulation, automatic tube current modulation with thyroid shield, and organ-based dose modulation with thyroid shield protocols reduced the thyroid dose by 28%, 33%, and 45%, respectively, compared with the use of automatic tube current modulation alone (p ≤ 0.005). Organ-based dose modulation also reduced the radiation dose to the ocular lens (33-47%) compared with the use of automatic tube current modulation (p ≤ 0.04). There was no significant difference in measured noise and subjective image quality between the protocols. Both organ-based dose modulation and thyroid shields significantly reduce the thyroid organ dose without degradation of subjective image quality compared with automatic tube current modulation. Organ-based dose modulation has the additional benefit of dose reduction to the ocular lens.
    American Journal of Roentgenology 05/2012; 198(5):1132-8. · 2.90 Impact Factor
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    ABSTRACT: We measured organ specific radiation dose rates and determined effective dose rates during simulated ureteroscopy using a validated model. To calculate the effective dose, patients were exposed to ureteroscopic management of stones at our institution. A validated anthropomorphic male phantom was placed on a fluoroscopy table and underwent simulated ureteroscopy. High sensitivity metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ sites in the phantom and used to measure organ specific radiation doses. These dose rates were multiplied by the appropriate tissue weighting factor and summed to calculate effective dose rates. Also, we retrospectively reviewed the charts of patients who underwent ureteroscopy at our institution. A total of 30 nonobese males with data on fluoroscopy time were included in analysis. The median effective dose was determined by multiplying median fluoroscopy time by the effective dose rate. The skin entrance was exposed to the highest absorbed dose rate, followed by the small intestine (mean ± SD 0.3286 ± 0.0054 and 0.1882 ± 0.0194 mGy per second, respectively). The mean effective dose rate was 0.024 ± 0.0019 mSv per second. Median fluoroscopy time was 46.95 seconds (range 12.9 to 298.8). The median effective dose was 1.13 mSv (range 0.31 to 7.17). The fluoroscopy used during ureteroscopy contributes to overall radiation exposure in patients with nephrolithiasis. Nonobese males are exposed to a median of 1.13 mSv during ureteroscopy, similar to that of abdominopelvic x-ray. More data are needed to determine clinical implications but urologists must be aware and decrease patient radiation during ureteroscopy.
    The Journal of urology 03/2012; 187(3):920-4. · 4.02 Impact Factor
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    ABSTRACT: The purpose of this study was to assess the effect of peak kilovoltage on radiation dose and image quality in adult neck MDCT. An anthropomorphic phantom with metal oxide semiconductor field effect transistor detectors was imaged with a 64-MDCT scanner. The reference CT protocol called for 120 kVp, and images obtained with that protocol were compared with CT images obtained with protocols entailing 80, 100, and 140 kVp. All imaging was performed with automatic tube current modulation. Organ dose and effective dose were determined for each protocol and compared with those obtained with the 120-kVp protocol. Image noise was evaluated objectively and subjectively for each protocol. The highest organ doses for all protocols were to the thyroid, ocular lens, skin, and mandible. The greatest reductions in organ dose were for the bone marrow of the cervical spine and mandible: 43% and 35% with the 100-kVp protocol and 63% and 53% with the 80-kVp protocol. Effective dose decreased as much as 9% with the 100-kVp protocol and 12% with the 80-kVp protocol. Use of the 140-kVp protocol was associated with an increase in organ dose as high as 64% for bone marrow in the cervical spine and a 19% increase in effective dose. Image noise increased with lower peak kilovoltage. The measured noise difference was greatest at 80 kVp, absolute increases were less than 2.5 HU. There was no difference in subjective image quality among protocols. Reducing the voltage from 120 to 80 kVp for neck CT can result in greater than 50% reduction in the absorbed organ dose to the bone marrow of the cervical spine and mandible without impairment in subjective image quality.
    American Journal of Roentgenology 03/2012; 198(3):621-7. · 2.90 Impact Factor
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    ABSTRACT: The purpose of this article is to compare the radiation dose of conventional fluoroscopy-guided lumbar epidural steroid injections (ESIs) and CT fluoroscopy (CTF)-guided lumbar ESI using both clinical data and anthropomorphic phantoms. We performed a retrospective review of dose parameters for 14 conventional fluoroscopy ESI procedures performed by one proceduralist and 42 CTF-guided ESIs performed by three proceduralists (14 each). By use of imaging techniques similar to those for our clinical cohorts, a commercially available anthropomorphic male phantom with metal oxide semiconductor field effect transistor detectors was scanned to obtain absorbed organ doses for conventional fluoroscopy-guided and CTF-guided ESIs. Effective dose (ED) was calculated from measured organ doses. The mean conventional fluoroscopy time for ESI was 37 seconds, and the mean procedural CTF time was 4.7 seconds. Calculated ED for conventional fluoroscopy was 0.85 mSv compared with 0.45 mSv for CTF. The greatest contribution to the radiation dose from CTF-guided ESI came from the planning lumbar spine CT scan, which had an ED of 2.90 mSv when z-axis ranged from L2 to S1. This resulted in a total ED for CTF-guided ESI (lumbar spine CT scan plus CTF) of 3.35 mSv. The ED for the CTF-guided ESI was almost half that of conventional fluoroscopy because of the shorter fluoroscopy time. However, the overall radiation dose for CTF-guided ESIs can be up to four times higher when a full diagnostic lumbar CT scan is performed as part of the procedure. Radiation dose reduction for CTF-guided ESI is best achieved by minimizing the dose from the preliminary planning lumbar spine CT scan.
    American Journal of Roentgenology 10/2011; 197(4):778-82. · 2.90 Impact Factor
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    ABSTRACT: Radiation exposure during medical procedures continues to be an increasing concern for physicians and patients. We determined organ-specific dose rates and calculated effective dose rates during right and left percutaneous nephrolithotomy (PCNL) using a validated phantom model. A validated anthropomorphic adult male phantom was placed prone on an operating room table. Metal oxide semiconductor field effect transistor dosimeters were placed at 20 organ locations in the model and were used to measure the organ dosages. A portable C-arm was used to provide continuous fluoroscopy for three 10 minute runs each to simulate a left and right PCNL. Organ dose rate (mGy/s) was determined by dividing organ dose by fluoroscopy time. The organ dose rates were multiplied by their tissue weighting factor and summed to determine effective dose rate (EDR) (mSv/s). Two-dimensional radiation distribution in the abdomen during a left-sided PCNL was visually determined using radiochromic film. The EDR for a left PCNL was 0.021 mSv/s ± 0.0008. The EDR for a right PCNL was 0.014 mSv/s ± 0.0004. The skin entrance was exposed to the greatest amount of radiation during left and right PCNL, 0.24 mGy/s and 0.26 mGy/s, respectively. Radiochromic film demonstrates visually the nonuniform dose distribution as the x-ray beam enters through the skin from the radiation source. The effective dose rate is higher for a left-sided PCNL compared with a right-sided PCNL. The distribution of radiation exposure during PCNL is not uniform. Further studies are needed to determine the long-term implications of these radiation doses during percutaneous stone removal.
    Journal of endourology / Endourological Society 09/2011; 26(5):439-43. · 1.75 Impact Factor
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    ABSTRACT: The purpose of this study was to measure organ doses and the effective dose (ED) using a three-dimensional rotational X-ray (3D-RX) system and to determine the ED conversion factor from the dose area product (DAP) for skull, spine and biliary protocols. A commercial 3D-RX imaging system was used to simulate the protocols with the adult female anthropomorphic phantom. Twenty MOSFET detectors were used to measure the absorbed doses at various organ locations. The ED was calculated for each protocol and the corresponding DAP was obtained. The skin dose was the highest for all the protocols. The second highest organ doses were those of the brain for the skull, the intestine for the spine and the kidney for the biliary protocol. The ED was 0.4-0.9, 4.2-8.4 and 3.2-4.6 mSv, and the ED conversion factor was 0.06-0.09, 0.18-0.31 and 0.13-0.23 mSv Gy(-1) cm(-2) for each protocol, respectively. This data may be used to estimate the patient ED for those protocols in the 3D-RX.
    Radiation Protection Dosimetry 09/2011; 150(1):50-4. · 0.91 Impact Factor
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    ABSTRACT: A dual modality SPECT-CT prototype system dedicated to uncompressed breast imaging (mammotomography) has been developed. The computed tomography subsystem incorporates an ultrathick K-edge filtration technique producing a quasi-monochromatic x-ray cone beam that optimizes the dose efficiency of the system for lesion imaging in an uncompressed breast. Here, the absorbed dose in various geometric phantoms and in an uncompressed and pendant cadaveric breast using a normal tomographic cone beam imaging protocol is characterized using both thermoluminescent dosimeter (TLD) measurements and ionization chamber-calibrated radiochromic film. Initially, two geometric phantoms and an anthropomorphic breast phantom are filled in turn with oil and water to simulate the dose to objects that mimic various breast shapes having effective density bounds of 100% fatty and glandular breast compositions, respectively. Ultimately, an excised human cadaver breast is tomographically scanned using the normal tomographic imaging protocol, and the dose to the breast tissue is evaluated and compared to the earlier phantom-based measurements. Measured trends in dose distribution across all breast geometric and anthropomorphic phantom volumes indicate lower doses in the medial breast and more proximal to the chest wall, with consequently higher doses near the lateral peripheries and nipple regions. Measured doses to the oil-filled phantoms are consistently lower across all volume shapes due to the reduced mass energy-absorption coefficient of oil relative to water. The mean measured dose to the breast cadaver, composed of adipose and glandular tissues, was measured to be 4.2 mGy compared to a mean whole-breast dose of 3.8 and 4.5 mGy for the oil- and water-filled anthropomorphic breast phantoms, respectively. Assuming rotational symmetry due to the tomographic acquisition exposures, these results characterize the 3D dose distributions in an uncompressed human breast tissue volume for this dedicated breast imaging device and illustrate advantages of using the novel ultrathick K-edge filtered beam to minimize the dose to the breast during fully-3D imaging.
    Medical Physics 06/2011; 38(6):3232-45. · 2.91 Impact Factor
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    ABSTRACT: Radiation and wound combined injury represents a major clinical challenge because of the synergistic interactions that lead to higher morbidity and mortality than either insult would produce singly. The purpose of this study was to develop a mouse ear punch model to study the physiological mechanisms underlying radiation effects on healing wounds. Surgical wounds were induced by a 2 mm surgical punch in the ear pinnae of MRL/MpJ mice. Photographs of the wounds were taken and the sizes of the ear punch wounds were quantified by image analysis. Local radiation to the ear was delivered by orthovoltage X-ray irradiator using a specially constructed jig that shields the other parts of body. Using this model, we demonstrated that local radiation to the wound area significantly delayed the healing of ear punch wounds in a dose-dependent fashion. The addition of sublethal whole body irradiation (7 Gy) further delayed the healing of ear punch wounds. These results were replicated in C57BL/6 mice; however, wound healing in MRL/MpJ mice was accelerated. These data indicate that the mouse ear punch model is a valuable model to study radiation and wound combined injury.
    International Journal of Radiation Biology 04/2011; 87(8):869-77. · 1.84 Impact Factor
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    ABSTRACT: Current methods for estimating and reporting radiation dose from CT examinations are largely patient-generic; the body size and hence dose variation from patient to patient is not reflected. Furthermore, the current protocol designs rely on dose as a surrogate for the risk of cancer incidence, neglecting the strong dependence of risk on age and gender. The purpose of this study was to develop a method for estimating patient-specific radiation dose and cancer risk from CT examinations. The study included two patients (a 5-week-old female patient and a 12-year-old male patient), who underwent 64-slice CT examinations (LightSpeed VCT, GE Healthcare) of the chest, abdomen, and pelvis at our institution in 2006. For each patient, a nonuniform rational B-spine (NURBS) based full-body computer model was created based on the patient's clinical CT data. Large organs and structures inside the image volume were individually segmented and modeled. Other organs were created by transforming an existing adult male or female full-body computer model (developed from visible human data) to match the framework defined by the segmented organs, referencing the organ volume and anthropometry data in ICRP Publication 89. A Monte Carlo program previously developed and validated for dose simulation on the LightSpeed VCT scanner was used to estimate patient-specific organ dose, from which effective dose and risks of cancer incidence were derived. Patient-specific organ dose and effective dose were compared with patient-generic CT dose quantities in current clinical use: the volume-weighted CT dose index (CTDIvol) and the effective dose derived from the dose-length product (DLP). The effective dose for the CT examination of the newborn patient (5.7 mSv) was higher but comparable to that for the CT examination of the teenager patient (4.9 mSv) due to the size-based clinical CT protocols at our institution, which employ lower scan techniques for smaller patients. However, the overall risk of cancer incidence attributable to the CT examination was much higher for the newborn (2.4 in 1000) than for the teenager (0.7 in 1000). For the two pediatric-aged patients in our study, CTDIvol underestimated dose to large organs in the scan coverage by 30%-48%. The effective dose derived from DLP using published conversion coefficients differed from that calculated using patient-specific organ dose values by -57% to 13%, when the tissue weighting factors of ICRP 60 were used, and by -63% to 28%, when the tissue weighting factors of ICRP 103 were used. It is possible to estimate patient-specific radiation dose and cancer risk from CT examinations by combining a validated Monte Carlo program with patient-specific anatomical models that are derived from the patients' clinical CT data and supplemented by transformed models of reference adults. With the construction of a large library of patient-specific computer models encompassing patients of all ages and weight percentiles, dose and risk can be estimated for any patient prior to or after a CT examination. Such information may aid in decisions for image utilization and can further guide the design and optimization of CT technologies and scan protocols.
    Medical Physics 01/2011; 38(1):408-19. · 2.91 Impact Factor

Publication Stats

828 Citations
147.10 Total Impact Points

Institutions

  • 2013
    • University of Texas Medical School
      Houston, Texas, United States
  • 2012–2013
    • Cincinnati Children's Hospital Medical Center
      Cincinnati, Ohio, United States
  • 2007–2011
    • Duke University Medical Center
      • Department of Radiology
      Durham, NC, United States
  • 2008
    • Inselspital, Universitätsspital Bern
      Berna, Bern, Switzerland
    • Duke University
      • Department of Biomedical Engineering (BME)
      Durham, NC, United States