JOURNAL OF ENDOUROLOGY Volume 30, Number 1, January 2016 ª Mary Ann Liebert, Inc. Pp. 57–62 DOI: 10.1089/end.2015.0419
Radiation Dosimetry for Ureteroscopy Patients: A Phantom Study Comparing the Standard and Obese Patient Models Richard H. Shin, MD,1 Fernando J. Cabrera, MD,1 Giao Nguyen, MS,2,6 Chu Wang, MS,2,5 Ramy F. Youssef, MD,3 Charles D. Scales, MD, MSHS,1,4 Michael N. Ferrandino, MD,1 Glenn M. Preminger, MD,1 Terry T. Yoshizumi, PhD, MS,2,6,7 and Michael E. Lipkin, MD1
Abstract
Purpose: To determine the effect of obesity on radiation exposure during simulated ureteroscopy. Methods: A validated anthropomorphic adult male phantom with a body mass index (BMI) of approximately 24 kg/m2, was positioned to simulate ureteroscopy. Padding with radiographic characteristics of human fat was placed around the phantom to create an obese model with BMI of 30 kg/m2. Metal oxide semiconductor field effect transistor (MOSFET) dosimeters were placed at 20 organ locations in both models to measure organ dosages. A portable C-arm was used to provide fluoroscopic x-ray radiation to simulate ureteroscopy. Organ dose rates were calculated by dividing organ dose by fluoroscopy time. Effective dose rate (EDR, mSv/sec) was calculated as the sum of organ dose rates multiplied by corresponding ICRP 103 tissue weighting factors. Results: The mean EDR was significantly increased during left ureteroscopy in the obese model at 0.0092 – 0.0004 mSv/sec compared with 0.0041 – 0.0003 mSv/sec in the nonobese model (P < 0.01), as well as during right ureteroscopy at 0.0061 – 0.0002 and 0.0036 – 0.0007 mSv/sec in the obese and nonobese model, respectively (P < 0.01). EDR during left ureteroscopy was significantly greater than right ureteroscopy in the obese model (P = 0.02). Conclusions: Fluoroscopy during ureteroscopy contributes to the overall radiation dose for patients being treated for nephrolithiasis. Obese patients are at even higher risk because of increased exposure rates during fluoroscopy. Every effort should be made to minimize the amount of fluoroscopy used during ureteroscopy, especially with obese patients. this study was to estimate the effect of obesity on radiation exposure rates with fluoroscopy during ureteroscopy. We used a validated model to measure OSDR and calculate the EDR.
Introduction
T
here is growing concern over radiation exposure during the management of nephrolithiasis. Patients are exposed to radiation during work-up, follow-up, as well as endourologic procedures using intraoperative fluoroscopy. Furthermore, obesity has been linked with nephrolithiasis.1 Obesity has already been observed to increase the effective dose patients are exposed to during CT scans as well as fluoroscopy used during percutaneous nephrolithotomy.2,3 Obesity is also linked with increased organ-specific dose rates (OSDR) during ureteroscopy.4 Quantification of effective dose rates (EDR) during ureteroscopy is important because fluoroscopy is commonly used. Furthermore, the effect of obesity on EDR during ureteroscopy has not yet been studied. Therefore, the purpose of
Materials and Methods
An anthropormorphic 173 cm tall, 73 kg Model 701-D male phantom (CIRS, Norfolk, VA) validated for human organ dosimetry measurements was used for testing and has an approximate body mass index (BMI) of 24 kg/m2. The phantom consists of 39 contiguous axial slices, each 25 mm thick. Within the slices are numbered locations representing the anatomic sites of internal organs, optimized for organ dosimetry. In addition, two rings of Custom Fat Layers for Model 701-D (E1397-1 and E1397-2) validated for dosimetry were
1
Comprehensive Kidney Stone Center, 2Radiation Safety Division, Duke University Medical Center, Durham, North Carolina. Urology Department, University of California, Irvine, Orange, California. 4 Duke Clinical Research Institute, 5Graduate Program of Medical Physics, 6Department of Radiology, 7Department of Radiation Oncology, Duke University, Durham, North Carolina. 3
57
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SHIN ET AL.
FIG. 1. Adult male phantom model. Nonobese model (A), axial section with numbers representing renal organ sites (B), and obese model (C). applied to simulate an obese patient with a BMI of 30 kg/m2 (Fig. 1). Fat layers were 22 cm wide and 4 cm thick, with the inner layer 94 cm long, and the outer layer 118 cm long. High sensitivity Model TN-1002RD metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters (Best Medical, Ottawa, Ontario, Canada) were used to measure the radiation dose at specified organ locations within the phantom. An OEC 9800 Plus C-arm (GE, Little Chalfont, UK) was used to perform fluoroscopy. Twenty MOSFET dosimeters were placed in specific organ locations within the model. For testing, the phantom was positioned with or without the simulated fat layers on a ureteroscopy table (IDI 100UC, Image Diagnostics, Fitchburg, MA) in standard position for a ureteroscopic procedure. The C-arm was positioned over the left or right upper abdomen with the source below the table. The image was collimated in the straight anteroposterior orientation over the approximate anatomic location of the renal units. Bony landmarks were used to ensure consistent unilateral placement and collimation. For all runs, the fluoroscopy unit was set at automatic exposure rate control at the pulsed (8 per second), low dose setting as is our standard clinical practice. For the nonobese phantom model, fluoroscopy was performed in three 5minute runs with actual settings automated to 83 to 84 kVp, 1.05 to 1.09 mA. In the obese phantom model, fluoroscopy was performed in three 7 to 10 minute runs with actual settings automated to 100 to 111 kVp, 1.5 to 3.36 mA. The duration of the fluoroscopy runs was not meant to mimic exposure time during ureteroscopy; rather, it was used to calculate exposure rates independent of overall time. Longer exposure time for the obese model was necessary to ensure MOSFET dosimeters accumulated enough radiation dose for measurement accuracy. Specific absorbed radiation dose in mGy was measured from each organ location. For the skin, red bone marrow (RBM), and bone surface, volumetric correction factors were applied to their absorbed dose readings to account for their partially irradiated volumes, because the dosimeter readings only reflect the absorbed dose measured in the field of view. For the skin, relative exposed area of exposure were esti-
mated to be 18% of the total skin area, based on the ‘‘rule of nines,’’ which is often used to estimate the percentage of burn of the skin. For the RBM, dosimeter readings from various locations were multiplied by the distribution of RBM in different bones of a standard man.5 For the bone surface, an estimated 20% correction factor was applied based on the skeletal mass distribution in the general region in the field of view.6 The correction can be expressed in the following formula: Daverage ¼ v Dmeasured
(1)
where Daverage is the average organ dose, v is the volumetric correction factor for the partially irradiated organs, and Dmeasured is average dosimeter readings for each of the partially irradiated organs. This method of volumetric correction for organ dose has been previously reported by Wang and associates7 and Fujii and colleagues.8 The effective dose, in mSv, was calculated with the absorbed doses of all organs using the standard ICRP 103 formulation and tissue weighting factors, which was then normalized to EDR, in mSv/s.9 To estimate the total effective dose received during ureteroscopy, several studies that report ureteroscopy times were collected.4,10–12 Procedural effective dose was calculated by multiplying EDR by referenced procedure time. Statistics were performed with JMP (SAS Institute, Cary, NC). Type I error rate was set at a = 0.05, with two-sided statistical t tests. A Holm-Bonferroni method was applied for multiple comparisons in the EDR data. Values are reported as mean – standard deviation unless otherwise specified. Results
The calculated EDRs for the obese phantom model were significantly greater than those of the nonobese phantom model (Fig. 2). For right ureteroscopy, the obese EDR was 0.0061 – 0.0002 mSv/sec while the nonobese rate was 0.0036 – 0.0007 mSv/sec (P < 0.01). For left ureteroscopy, the EDR for obese and nonobese phantom models were
RADIATION DOSE WITH OBESITY DURING URS
FIG. 2. Radiation exposure rate during ureteroscopy (URS). Total effective dose rates for right and left URS in obese (gray) and nonobese (white) models. *P < 0.01.
59
0.0092 – 0.0004 mSv/sec and 0.0041 – 0.0003 mSv/sec, respectively (P < 0.01). The difference between right and left EDR in the obese phantom model was significant (P = 0.02), whereas the difference in the nonobese phantom model was not (P = 0.063). Individual OSDR between the obese and nonobese phantom model in right and left ureteroscopy are presented in Figure 3. During right ureteroscopy in the obese phantom model, organs receiving the greatest radiation exposure rates included the adrenals, kidneys, skin, and liver. During left ureteroscopy in the obese phantom model, organs receiving the most radiation exposure rates included the skin, kidneys, spleen, and pancreas/transverse colon. There was a large difference in skin entrance dose rates without partial-volume correction between the obese (0.35 – 0.11 mGy/sec) and nonobese (0.07 – 0.01 mGy/sec) phantom models (P = 0.001).
FIG. 3. Individual organ exposure rates. Measured organ dose rates for simulated right and left ureteroscopy in obese (gray) and nonobese (white) models. Organs organized by decreasing significance to radiation dose, or WT (tissue weighting factor). *P > 0.05.
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SHIN ET AL.
Table 1. Estimated Effective Dose During Ureteroscopy Estimated effective dose (mSev)
Study Rebuck et al. Ngo et al.11
10
Greene et al.12 Hsi et al.4
Condition
Fluoroscopy time (s)
BMI (mean, range)
Renal stone Prefeedback, 27% renal stone Postfeedback, 25% renal stone Preprotocol Postprotocol Minimal-use protocol
313.8 164.4 124.8 85.1 15.5 4.2
30.8 (16–55) 25% obese 19% obese 29.7 (19.8–45.5) 26.4 (18–41) 30.8 (15.2–61.6)
Calculated total effective doses during ureteroscopy based on published fluoroscopy times varied widely (Table 1). Depending on radiation use protocol, reported mean fluoroscopy times ranged from 313.8 seconds to 4.2 seconds. The calculated ED ranged from 0.03 to 2.89 mSv for the obese phantom model compared with 0.01 to 1.27 mSv for the nonobese phantom model. Discussion
We have demonstrated greater relative radiation exposure rates in both individual organs and effective dose in obese patients. The EDR was approximately double in an obese patient compared with a nonobese patient model. The significance of this model is twofold. First, obesity has been linked to greater risk for stone disease. Taylor and coworkers1 observed a relative risk for symptomatic kidney stones of 1.33, 1.9, and 2.09 for men, older women, and younger women, respectively, with a BMI of ‡30 kg/m2 versus those with a BMI of 21 to 22.9 kg/m2 (P < 0.001). This correlation has been observed in many other cohorts.13–15 Causes include associated diets high in lithogenic substances.16,17 Furthermore, obesity is linked to increased excretion of oxalate, uric acid, sodium, and phosphate.14,18,19 Finally, body weight is inversely related to urinary pH because of insulin resistance.19,20 This is especially important in the United States because the prevalence of obesity has been observed to rise from 1980 to 1999 and maintain high rates through 2010.21 Secondly, obese patients may already experience greater radiation exposure during the outpatient management of their stone disease. While BMI was not reported, Ferrandino and associates22 retrospectively observed that patients received an average of four radiographic examinations within 1 year after an acute stone event, and 20% received estimated doses greater than 50 mSv. Exposure was estimated based on accepted values of patient and stone characteristics. CT scans had a heavy contribution to radiation exposure. The average number of CTs for patients who received less than and greater than 50 mSv were 1 and 3.5, respectively. Wang and colleagues2 demonstrated that obesity (BMI 30 vs 24 kg/m2) results in more than triple the radiation exposure during a stone protocol CT using the same validated model in our tests. To our knowledge, this is the first study examining the effect of obesity on OSDR and calculated EDR during ureteroscopy using a validated model. Effective dose is an important measure because it relates radiation exposure to
Right ureteroscopy
Left ureteroscopy
Obese
Nonobese
Obese Nonobese
1.93 1.01 0.77 0.52 0.10 0.03
1.12 0.59 0.44 0.30 0.06 0.01
2.89 1.52 1.15 0.78 0.14 0.04
1.27 0.67 0.51 0.35 0.06 0.02
risk of malignancy. Unfortunately, effective dose cannot be directly measured and can only be estimated or calculated. Krupp and coworkers23 studied organ-specific doses in cadavers during simulated left ureteroscopy. Four male and four female cadavers underwent 145 seconds of fluoroscopy. Exposure to 11 organs was directly measured with thermoluminescent dosimeters. They observed a nonstatistically significant increase in dose for the kidneys, lungs, skin entrance, and cornea when stratifying cadavers by BMI below or above 30 kg/m2. Not enough organs were measured to estimate an effective dose, nor was the model validated. Hsi and colleagues4 estimated three-fold higher radiation dose rates in severely obese patients undergoing ureteroscopy.4 After collecting fluoroscopy dose and time, they reported increasing radiation dose rate with increasing BMI; 0.16 mGy/s for BMI
Radiation Dosimetry for Ureteroscopy Patients: A Phantom Study Comparing the Standard and Obese Patient Models Richard H. Shin, MD,1 Fernando J. Cabrera, MD,1 Giao Nguyen, MS,2,6 Chu Wang, MS,2,5 Ramy F. Youssef, MD,3 Charles D. Scales, MD, MSHS,1,4 Michael N. Ferrandino, MD,1 Glenn M. Preminger, MD,1 Terry T. Yoshizumi, PhD, MS,2,6,7 and Michael E. Lipkin, MD1
Abstract
Purpose: To determine the effect of obesity on radiation exposure during simulated ureteroscopy. Methods: A validated anthropomorphic adult male phantom with a body mass index (BMI) of approximately 24 kg/m2, was positioned to simulate ureteroscopy. Padding with radiographic characteristics of human fat was placed around the phantom to create an obese model with BMI of 30 kg/m2. Metal oxide semiconductor field effect transistor (MOSFET) dosimeters were placed at 20 organ locations in both models to measure organ dosages. A portable C-arm was used to provide fluoroscopic x-ray radiation to simulate ureteroscopy. Organ dose rates were calculated by dividing organ dose by fluoroscopy time. Effective dose rate (EDR, mSv/sec) was calculated as the sum of organ dose rates multiplied by corresponding ICRP 103 tissue weighting factors. Results: The mean EDR was significantly increased during left ureteroscopy in the obese model at 0.0092 – 0.0004 mSv/sec compared with 0.0041 – 0.0003 mSv/sec in the nonobese model (P < 0.01), as well as during right ureteroscopy at 0.0061 – 0.0002 and 0.0036 – 0.0007 mSv/sec in the obese and nonobese model, respectively (P < 0.01). EDR during left ureteroscopy was significantly greater than right ureteroscopy in the obese model (P = 0.02). Conclusions: Fluoroscopy during ureteroscopy contributes to the overall radiation dose for patients being treated for nephrolithiasis. Obese patients are at even higher risk because of increased exposure rates during fluoroscopy. Every effort should be made to minimize the amount of fluoroscopy used during ureteroscopy, especially with obese patients. this study was to estimate the effect of obesity on radiation exposure rates with fluoroscopy during ureteroscopy. We used a validated model to measure OSDR and calculate the EDR.
Introduction
T
here is growing concern over radiation exposure during the management of nephrolithiasis. Patients are exposed to radiation during work-up, follow-up, as well as endourologic procedures using intraoperative fluoroscopy. Furthermore, obesity has been linked with nephrolithiasis.1 Obesity has already been observed to increase the effective dose patients are exposed to during CT scans as well as fluoroscopy used during percutaneous nephrolithotomy.2,3 Obesity is also linked with increased organ-specific dose rates (OSDR) during ureteroscopy.4 Quantification of effective dose rates (EDR) during ureteroscopy is important because fluoroscopy is commonly used. Furthermore, the effect of obesity on EDR during ureteroscopy has not yet been studied. Therefore, the purpose of
Materials and Methods
An anthropormorphic 173 cm tall, 73 kg Model 701-D male phantom (CIRS, Norfolk, VA) validated for human organ dosimetry measurements was used for testing and has an approximate body mass index (BMI) of 24 kg/m2. The phantom consists of 39 contiguous axial slices, each 25 mm thick. Within the slices are numbered locations representing the anatomic sites of internal organs, optimized for organ dosimetry. In addition, two rings of Custom Fat Layers for Model 701-D (E1397-1 and E1397-2) validated for dosimetry were
1
Comprehensive Kidney Stone Center, 2Radiation Safety Division, Duke University Medical Center, Durham, North Carolina. Urology Department, University of California, Irvine, Orange, California. 4 Duke Clinical Research Institute, 5Graduate Program of Medical Physics, 6Department of Radiology, 7Department of Radiation Oncology, Duke University, Durham, North Carolina. 3
57
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SHIN ET AL.
FIG. 1. Adult male phantom model. Nonobese model (A), axial section with numbers representing renal organ sites (B), and obese model (C). applied to simulate an obese patient with a BMI of 30 kg/m2 (Fig. 1). Fat layers were 22 cm wide and 4 cm thick, with the inner layer 94 cm long, and the outer layer 118 cm long. High sensitivity Model TN-1002RD metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters (Best Medical, Ottawa, Ontario, Canada) were used to measure the radiation dose at specified organ locations within the phantom. An OEC 9800 Plus C-arm (GE, Little Chalfont, UK) was used to perform fluoroscopy. Twenty MOSFET dosimeters were placed in specific organ locations within the model. For testing, the phantom was positioned with or without the simulated fat layers on a ureteroscopy table (IDI 100UC, Image Diagnostics, Fitchburg, MA) in standard position for a ureteroscopic procedure. The C-arm was positioned over the left or right upper abdomen with the source below the table. The image was collimated in the straight anteroposterior orientation over the approximate anatomic location of the renal units. Bony landmarks were used to ensure consistent unilateral placement and collimation. For all runs, the fluoroscopy unit was set at automatic exposure rate control at the pulsed (8 per second), low dose setting as is our standard clinical practice. For the nonobese phantom model, fluoroscopy was performed in three 5minute runs with actual settings automated to 83 to 84 kVp, 1.05 to 1.09 mA. In the obese phantom model, fluoroscopy was performed in three 7 to 10 minute runs with actual settings automated to 100 to 111 kVp, 1.5 to 3.36 mA. The duration of the fluoroscopy runs was not meant to mimic exposure time during ureteroscopy; rather, it was used to calculate exposure rates independent of overall time. Longer exposure time for the obese model was necessary to ensure MOSFET dosimeters accumulated enough radiation dose for measurement accuracy. Specific absorbed radiation dose in mGy was measured from each organ location. For the skin, red bone marrow (RBM), and bone surface, volumetric correction factors were applied to their absorbed dose readings to account for their partially irradiated volumes, because the dosimeter readings only reflect the absorbed dose measured in the field of view. For the skin, relative exposed area of exposure were esti-
mated to be 18% of the total skin area, based on the ‘‘rule of nines,’’ which is often used to estimate the percentage of burn of the skin. For the RBM, dosimeter readings from various locations were multiplied by the distribution of RBM in different bones of a standard man.5 For the bone surface, an estimated 20% correction factor was applied based on the skeletal mass distribution in the general region in the field of view.6 The correction can be expressed in the following formula: Daverage ¼ v Dmeasured
(1)
where Daverage is the average organ dose, v is the volumetric correction factor for the partially irradiated organs, and Dmeasured is average dosimeter readings for each of the partially irradiated organs. This method of volumetric correction for organ dose has been previously reported by Wang and associates7 and Fujii and colleagues.8 The effective dose, in mSv, was calculated with the absorbed doses of all organs using the standard ICRP 103 formulation and tissue weighting factors, which was then normalized to EDR, in mSv/s.9 To estimate the total effective dose received during ureteroscopy, several studies that report ureteroscopy times were collected.4,10–12 Procedural effective dose was calculated by multiplying EDR by referenced procedure time. Statistics were performed with JMP (SAS Institute, Cary, NC). Type I error rate was set at a = 0.05, with two-sided statistical t tests. A Holm-Bonferroni method was applied for multiple comparisons in the EDR data. Values are reported as mean – standard deviation unless otherwise specified. Results
The calculated EDRs for the obese phantom model were significantly greater than those of the nonobese phantom model (Fig. 2). For right ureteroscopy, the obese EDR was 0.0061 – 0.0002 mSv/sec while the nonobese rate was 0.0036 – 0.0007 mSv/sec (P < 0.01). For left ureteroscopy, the EDR for obese and nonobese phantom models were
RADIATION DOSE WITH OBESITY DURING URS
FIG. 2. Radiation exposure rate during ureteroscopy (URS). Total effective dose rates for right and left URS in obese (gray) and nonobese (white) models. *P < 0.01.
59
0.0092 – 0.0004 mSv/sec and 0.0041 – 0.0003 mSv/sec, respectively (P < 0.01). The difference between right and left EDR in the obese phantom model was significant (P = 0.02), whereas the difference in the nonobese phantom model was not (P = 0.063). Individual OSDR between the obese and nonobese phantom model in right and left ureteroscopy are presented in Figure 3. During right ureteroscopy in the obese phantom model, organs receiving the greatest radiation exposure rates included the adrenals, kidneys, skin, and liver. During left ureteroscopy in the obese phantom model, organs receiving the most radiation exposure rates included the skin, kidneys, spleen, and pancreas/transverse colon. There was a large difference in skin entrance dose rates without partial-volume correction between the obese (0.35 – 0.11 mGy/sec) and nonobese (0.07 – 0.01 mGy/sec) phantom models (P = 0.001).
FIG. 3. Individual organ exposure rates. Measured organ dose rates for simulated right and left ureteroscopy in obese (gray) and nonobese (white) models. Organs organized by decreasing significance to radiation dose, or WT (tissue weighting factor). *P > 0.05.
60
SHIN ET AL.
Table 1. Estimated Effective Dose During Ureteroscopy Estimated effective dose (mSev)
Study Rebuck et al. Ngo et al.11
10
Greene et al.12 Hsi et al.4
Condition
Fluoroscopy time (s)
BMI (mean, range)
Renal stone Prefeedback, 27% renal stone Postfeedback, 25% renal stone Preprotocol Postprotocol Minimal-use protocol
313.8 164.4 124.8 85.1 15.5 4.2
30.8 (16–55) 25% obese 19% obese 29.7 (19.8–45.5) 26.4 (18–41) 30.8 (15.2–61.6)
Calculated total effective doses during ureteroscopy based on published fluoroscopy times varied widely (Table 1). Depending on radiation use protocol, reported mean fluoroscopy times ranged from 313.8 seconds to 4.2 seconds. The calculated ED ranged from 0.03 to 2.89 mSv for the obese phantom model compared with 0.01 to 1.27 mSv for the nonobese phantom model. Discussion
We have demonstrated greater relative radiation exposure rates in both individual organs and effective dose in obese patients. The EDR was approximately double in an obese patient compared with a nonobese patient model. The significance of this model is twofold. First, obesity has been linked to greater risk for stone disease. Taylor and coworkers1 observed a relative risk for symptomatic kidney stones of 1.33, 1.9, and 2.09 for men, older women, and younger women, respectively, with a BMI of ‡30 kg/m2 versus those with a BMI of 21 to 22.9 kg/m2 (P < 0.001). This correlation has been observed in many other cohorts.13–15 Causes include associated diets high in lithogenic substances.16,17 Furthermore, obesity is linked to increased excretion of oxalate, uric acid, sodium, and phosphate.14,18,19 Finally, body weight is inversely related to urinary pH because of insulin resistance.19,20 This is especially important in the United States because the prevalence of obesity has been observed to rise from 1980 to 1999 and maintain high rates through 2010.21 Secondly, obese patients may already experience greater radiation exposure during the outpatient management of their stone disease. While BMI was not reported, Ferrandino and associates22 retrospectively observed that patients received an average of four radiographic examinations within 1 year after an acute stone event, and 20% received estimated doses greater than 50 mSv. Exposure was estimated based on accepted values of patient and stone characteristics. CT scans had a heavy contribution to radiation exposure. The average number of CTs for patients who received less than and greater than 50 mSv were 1 and 3.5, respectively. Wang and colleagues2 demonstrated that obesity (BMI 30 vs 24 kg/m2) results in more than triple the radiation exposure during a stone protocol CT using the same validated model in our tests. To our knowledge, this is the first study examining the effect of obesity on OSDR and calculated EDR during ureteroscopy using a validated model. Effective dose is an important measure because it relates radiation exposure to
Right ureteroscopy
Left ureteroscopy
Obese
Nonobese
Obese Nonobese
1.93 1.01 0.77 0.52 0.10 0.03
1.12 0.59 0.44 0.30 0.06 0.01
2.89 1.52 1.15 0.78 0.14 0.04
1.27 0.67 0.51 0.35 0.06 0.02
risk of malignancy. Unfortunately, effective dose cannot be directly measured and can only be estimated or calculated. Krupp and coworkers23 studied organ-specific doses in cadavers during simulated left ureteroscopy. Four male and four female cadavers underwent 145 seconds of fluoroscopy. Exposure to 11 organs was directly measured with thermoluminescent dosimeters. They observed a nonstatistically significant increase in dose for the kidneys, lungs, skin entrance, and cornea when stratifying cadavers by BMI below or above 30 kg/m2. Not enough organs were measured to estimate an effective dose, nor was the model validated. Hsi and colleagues4 estimated three-fold higher radiation dose rates in severely obese patients undergoing ureteroscopy.4 After collecting fluoroscopy dose and time, they reported increasing radiation dose rate with increasing BMI; 0.16 mGy/s for BMI
