Lifetime Radiation Exposure in Patients with ...

Curr Urol Rep (2017) 18:85 DOI 10.1007/s11934-017-0731-6

NEW IMAGING TECHNIQUES (S RAIS-BAHRAMI AND A GEORGE, SECTION EDITORS)

Lifetime Radiation Exposure in Patients with Recurrent Nephrolithiasis Mohamed A. Elkoushy 1 & Sero Andonian 2

# Springer Science+Business Media, LLC 2017

Abstract Patients presenting with nephrolithiasis often undergo repeated imaging studies before, during, and after management. Considering the significant risk of stone recurrence in primary stone-formers, repeated imaging studies are not uncommon. Cumulative effects of ionizing radiation exposure from various imaging studies could potentially increase the risk for developing cataracts and solid malignancies in urolithiasis patients. Therefore, practitioners planning or performing imaging studies with ionizing radiation are compelled to keep radiation exposure to humans and the environment as low as possible, thus strictly adhering to the ALARA (As Low as Reasonably Achievable) principles. This chapter will review the latest literature on lifetime radiation exposure of nephrolithiasis patients and present the latest recommendations in minimizing radiation exposure to them pre-, intra-, and postoperatively. For patients presenting with acute renal colic, especially those with body mass index of < 30, low-dose noncontrast computed tomography is the current gold standard of imaging. Patients with opaque stones are followed with ultrasonography (US) and plain radiography (kidney, ureter, and bladder or KUB). Intraoperatively, pulsed fluoroscopy could be used to significantly reduce radiation during ureteroscopy and percutaneous nephrolithotomy. Immediately postoperatively This article is part of the Topical Collection on New Imaging Techniques * Sero Andonian [email protected] Mohamed A. Elkoushy [email protected] 1

Department of Urology, Suez Canal University, Ismailia, Egypt

2

Department of Surgery, Division of Urology, McGill University Health Centre, 1001 Boulevard Decarie, Suite D05.5331, Montreal, QC H4A 3J1, Canada

and in the long term, US and KUB could be used to follow up patients with nephrolithiasis. Only symptomatic patients suspected of ureteral stricture should obtain tri-phasic CT urography. Following these latest imaging guidelines from the American Urological Association will dramatically reduce lifetime radiation exposure to patients with nephrolithiasis. Keywords Radiation exposure . Nephrolithiasis . Ionizing . Computed tomography . Kidney stones . Imaging technique

Introduction The prevalence of nephrolithiasis has increased by almost 70% over the last 15 years and approximately 1 in 11 Americans develop kidney stones [1, 2]. Consequently, the number of imaging studies ordered to evaluate nephrolithiasis has also increased. Radiological imaging remains the cornerstone of diagnosis and follow-up of patients with nephrolithiasis, representing a significant portion of all imaging requested by urologists [3]. Noncontrast computed tomography (NCCT) scan of the abdomen and pelvis provides the most accurate diagnosis, but it is the main source of ionizing radiation exposure related to medical imaging. Ultrasonography (US) does not need the use of radiation, but its sensitivity and specificity for stone detection is much lower than NCCT. Therefore, selection of the appropriate imaging modality for nephrolithiasis may be impacted by the patients’ body mass index (BMI), cost, and clinical setting as well as tolerance to ionizing radiation [4]. Nevertheless, the number of CT scans performed for imaging patients with nephrolithiasis has tripled in recent years [5], and its widespread use represents the single most important advance in diagnostic radiology [6]. However, a considerable risk of cancer-related mortality has been reported at 1/100,000

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individuals with exposure to a radiation dose as low as 100 millisieverts (mSv) [7]. Although radiation exposure of a single radiograph is relatively low, accumulated doses from repeated studies for recurrent stone-formers would increase the risk of radiation-induced hazards [8]. Prolonged radiation exposures are believed to be more harmful than single acute exposures. Preston and associates have reported a significant association between low-dose radiation exposure and both solid and hematologic malignancies, at doses as low as 5 mSv in some reports [6, 9–11]. The International Commission on Radiological Protection (ICRP) has therefore placed thresholds for safe exposure of 50 mSv for a single year or 20 mSv per year for a period of 5 years [12]. However, 17–20% of patients with nephrolithiasis received more than 50 mSv during their first year of follow-up [13, 14•]. Furthermore, the risk of exceeding this limit increased in patients with multiple stone locations when compared with those with single stones [15]. While one fifth of patients surpassed the ICRE limit for the first year of followup after an acute renal colic, none of the patients surpassed the 50-mSv limit during the second year follow-up due to significantly higher use of US than NCCT scans during the second year of follow-up [14•]. While both of these studies were alarming, both were published prior to the implementation of low-dose CT scans and the publication of the imaging guidelines from the American Urological Association (AUA) as described below. In this review, different imaging modalities for diagnosis and follow-up of nephrolithiasis will be presented together with the hazards of radiation exposure. In addition, the latest imaging guidelines from the AUA will be emphasized during diagnosis and follow-up. Furthermore, intraoperative maneuvers such as pulse fluoroscopy will be presented as tools to reduce intraoperative radiation. Finally, literature on lifetime radiation exposure in recurrent stone-formers will be reviewed. Hazards of Radiation Exposure Ionizing radiation is defined as radiation that has sufficient energy to displace electrons from molecules, which in turn can damage human cells. It comprises electromagnetic radiation, such as X-rays and gamma rays (γ-rays), or subatomic particles, including protons, neutrons, and α-particles. X- and γ-rays are known to be sparsely ionizing due to its production of fast electrons, causing a few dozen ionizations when they navigate a cell. Radiation exposure is measured in terms of the quantity of energy absorbed per unit of body mass, as joules per kilogram (J/kg), and is typically reported in Gray (Gy). Since radiation is differently absorbed by various body organs, the millisievert (mSv) is used to estimate the effective radiation dose (ERD). It accounts for the biological sensitivity of different organs and measures the overall harm to the patient. The ICRP has established thresholds for “safe” radiation exposure. However, the Biological Effects of Ionizing

Curr Urol Rep (2017) 18:85

Radiation Committee (BEIR) concluded that there is a linear, no-threshold dose–response link between exposure to ionizing radiation and the development of malignancies [8]. Health effects of ionizing radiation mostly came from the thoroughly studied survivors of the Hiroshima and Nagasaki atomic bombs, where two thirds of them received low dose of radiation, defined as less than 100 mSv [8]. Clinically, these data may have its shortcomings and its population is greatly different from patients undergoing imaging procedures. However, there is no alternative long-term evidence available to assess the impact of radiation exposure. Well-documented late effects of radiation exposure include the induction of malignancies, including solid cancer and leukemia, and some degenerative diseases such as cataracts. Induction of DNA mutations of germ cells has been demonstrated in animal studies, where they may cause adverse health effects in their offsprings. Excess cancer risk has been observed at dose levels of 100 to 4000 mSv, while excess cancers can be detected at doses as low as 10 mSv during in utero exposure. Within 15 years of exposure, there was increased risk of leukemia, whereas the risk of solid malignancy increased with increasing doses of radiation exposure throughout life, regardless of age at exposure [11, 16]. Therefore, children and adolescents have a higher lifetime risk of malignancy due to the more years they are expected to live and the more radiosensitive tissues they have than adults [11, 17]. In nuclear workers with protracted exposure to low-dose radiation, risks of solid cancer and leukemia significantly increased with average exposure doses of as low as 20 mSv. Two percent of cancer deaths in these workers were likely attributable to radiation exposure [18]. The BEIR committee has developed “risk models” to estimate the lifetime cancer risk in individuals exposed to lowdose radiation. Calculations in this report suggest that 42 out of 100 people are expected to develop solid cancers or leukemia in their lifetime, and 1 out of 100 people is expected to develop solid cancer or leukemia as a result of a single radiation exposure dose as low as 100 mSv above background [8]. While these risk estimates may not be accurate due to limitations of the data used to develop these risk models, they still raise concerns for development of solid cancers or leukemias in patients receiving excessive radiation exposure. Common Imaging Modalities for Urolithiasis Radiological imaging studies are crucial in diagnosis and follow-up of patients with nephrolithiasis and represent a significant portion of all imaging requested by urologists [3]. Radiation exposure caused by medical sources has increased from one sixth of the total dose in 1980 to greater than 50% in 2006 [19]. The average effective doses among standard radiographic examinations can vary by over 1/1000 portion (0.01– 10 mSv) (Tables 1 and 2). The average effective doses of CT scans and interventional procedures range from 2 to 20 mSv

Curr Urol Rep (2017) 18:85 Table 1 Standard effective radiation doses from common imaging studies

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Modality

Typical effective dose (mSv)

KUB plain X-ray IVU urography/retrograde pyelography Abdominal/pelvic single-detector CT

Male: 0.2–0.4; female: 0.7 Male: 1.33–1.6; female: 2.3–2.8 4.3–6.5

(200 mA, 120 kVp, pitch 1, 5-mm slices) Abdominal/pelvic multidetector CT

8.5

(200 mA, 120 kVp, pitch 0.75, 5-mm slices) Low-dose protocol multidetector CT

Male: 0.98; female: 1.5

(70 mA, 120 kVp, pitch 2, 5-mm slices) CT urogram (3 phases)

14.8

Adopted from Andonian and Atalla [20] CT computed tomography; IVU intravenous urography; KUB kidney, ureter, and bladder; kVp kilovoltage; mA milliampere; mSv millisievert

and 5–70 mSv, respectively [19]. The selection of a particular imaging modality for diagnosis or follow-up of nephrolithiasis may be impacted by patient-related, surgeon-related, and institutional-related factors. In the following section, the most common imaging modalities used for assessment of nephrolithiasis will be described. Conventional X-ray These include the abdominal KUB (kidney, ureter, and bladder) plain X-ray and the intravenous excretory urography (IVU). KUB alone is not acceptable as an initial tool in the acute setting since it fails to demonstrate radiolucent stones [21]. Moreover, no anatomical or functional information about obstruction can be obtained. KUB has a low sensitivity (44–77%), but higher specificity (80–87%) for detection of nephrolithiasis [22]. It is particularly useful in the follow-up after surgical or conservative treatment of a known radiopaque stone, and it can provide comparable stone size measurements to CT [23, 24]. The radiation dose varies from 0.5 to 0.8 mSv [25•]. Despite either KUB or US alone having their shortcomings in the primary stone work-up, the combination of both has been shown to yield diagnostic information comparable to CT [21]. Table 2 Comparison of different imaging studies for nephrolithiasis

KUB together with US has 79% sensitivity, 100% sensitivity, and 92–97% negative predictive value. However, they could miss stones smaller than 5 mm, especially those found in the mid- or distal ureter [26]. The addition of tomograms has been shown to increase the sensitivity of KUB, where additional calculi were detected in 37% of patients with KUB and linear tomography than KUB alone [27]. However, this combined imaging protocol would increase the dose of radiation, which has been shown to be greater than that of low-dose CT [28•]. The IVU has a sensitivity of 51–87% and specificity of 92– 100%. However, it is relatively contraindicated with acute colic and absolutely contraindicated in renal insufficiency and contrast medium allergy. The radiation dose varies from 1.4 to 3.9 mSv, depending on the type of X-ray machine [29]. The anatomy of the upper urinary tract can be assessed by the excretory urography and thus can help in choosing the definitive stone therapy. Ultrasonography Ultrasound examination uses high-frequency sound waves, and it is a non-ionizing radiation real-time imaging modality. Therefore, it does not have the risks of radiation exposure

Imaging modality

Sensitivitya

Specificitya

Cost multiple relative to of KUB

CTb Low-dose CT Ultrasonography KUB MRI

95% 95% 84% 57% 82%

98% 97% 53% 76% 98%

10 10 5 1 30

Adapted from Brisbane et al. [4] KUB kidney, ureters, and bladder plain film; CT computed tomography; MRI magnetic resonance imaging a

These values were published by the American College of Radiography and American Urological Association, which have obtained them from pooled data analysis

b

Radiation doses from CT depends on the machine and protocol

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similar to other types of imaging modalities. It is of particular benefit for diagnosis of obstruction. Its primary advantages include low cost, non-invasiveness, speed, and lack of ionizing radiation. It can be used for initial diagnosis and follow-up of nephrolithiasis, with a sensitivity of up to 96% in detecting renal or ureteral stones larger than 5 mm [30]. Moreover, US can be used as a diagnostic modality in pediatric and pregnant patients. In addition, US can be used in the treatment of urolithiasis, including US-guided access for percutaneous nephrolithotomy (PCNL), retrograde intrarenal surgery, and extracorporeal shock wave lithotripsy (SWL) [31]. A recent multicenter, randomized trial reported that initial US is not inferior to CT scans in acute colic, despite its lower sensitivity when compared with NCCT scans [32]. However, these results do not suggest that patients should undergo only the US in the initial work-up for stones, but rather it should be used as the initial diagnostic tool. Further imaging studies would be performed at the discretion of the clinician. Color Doppler US could identify 97.1% of ureteral stones, with a sensitivity and specificity of 97.2 and 99%, respectively [33]. Moreover, use of the twinkling sign on the Doppler US is a promising imaging modality for accurate identification of ureteral stones [34]. The accuracy of stone size determination by US could be significantly improved by measuring acoustic shadow width rather than stone width [35]. Accuracy of stone-specific algorithms (S-mode) in estimating the kidney stone size in in vivo studies demonstrated that stone size could be estimated within 1 mm of stone size on NCCT [36]. Therefore, with increasing awareness about radiation hazards and moving trends toward decreasing exposure from CT and fluoroscopy, US will increasingly have a prominent role as a “safe” radiation-free imaging modality in diagnosis and follow-up of nephrolithiasis. Nevertheless, US is an operator-dependent modality, and its sensitivity may be impacted by the skill and experience of the operator.

Computed Tomography Standard-dose NCCT was considered the gold standard in the diagnosis of nephrolithiasis, especially in the emergency setting, due to its speed, high sensitivity and accuracy in detection of stones, and its ability to diagnose alternative pathologies. It has superior sensitivity for ureteral, radiolucent, and smaller stones (< 5 mm) [22]. Standard-dose CT has a sensitivity of 98% and specificity of 100% for ureteral stones [21, 22]. Moreover, CT can accurately measure stone size and skin-to-stone distance and may provide additional information regarding stone composition, by measuring Hounsfield units (HFU). However, CT is expensive compared with US and KUB and exposes patients to the highest radiation dose compared with other imaging modalities. The effective radiation dose of a standard CT of the abdomen and pelvis performed


for assessment of urinary calculi has been reported to be as high as 9.6 mSv for men and 12.6 mSv for women [37]. Low-Dose CT Protocols Low-dose CT protocols have been introduced to decrease radiation exposure while maintaining image quality [38, 39]. Moreover, ultra-low-dose CT scans were recently investigated delivering an effective radiation dose of approximately 1 mSv and demonstrating accuracy for stone size of ≥ 4 mm [40••]. The sensitivity and specificity of these ultra-low-dose CT scans for stones < 3 and ≥ 3 mm were 74 and 77% and 92 and 82%, respectively [41]. However, these ultra-low-dose CTs were inferior to low-dose protocols for detecting stones < 3 mm. For patients with a BMI < 30 kg/m2, low-dose protocols can be used to minimize radiation exposure [42]. However, the image quality is lower in patients with higher BMI and the sensitivity and specificity drop to 50% and < 90%, respectively [39]. Low-dose CT (LDCT) protocols have been used to significantly minimize radiation dose by narrowing collimation and providing faster image acquisition [38, 39, 43]. The estimated ERD have been reported as low as 0.5 mSv without significantly compromising image quality [38]. However, LDCT may suffer from increased “noise” which consequently would impact image quality in obese patients [44] leading to decreased detection rates for small ureteral stones [39]. Ciaschini et al. determined the effect of 50 and 75% dose reduction on CT sensitivity and specificity for the detection of urolithiasis. For the 100, 50, and 25% reconstructions, all urinary calculi larger than 3 mm showed comparable combined sensitivities of 97.7, 93.0, and 91.9%, respectively [45]. Kim et al. prospectively compared LDCT (50 mA) with standard dose (260 mA) in 121 patients presenting with renal colic. Compared with the standard CT, mean ERD decreased more than 80% with the LDCT: 7.3 vs. 1.4 mSv for males and 10.0 vs. 1.97 mSv for females. Both sensitivity and specificity were comparable between the standard and LDCT for ureteral stone detection (99% vs. 93%/95% and 93% vs. 86%), while LDCT was less sensitive for detection of stones ≤ 2 mm (79 and 68%) [46]. Heldt et al. evaluated the impact of body weight on LDCT in the detection of ureteral calculi in three cadavers of increasing weight (55, 85, and 115 kg) with 721 calcium oxalate stones. Compared with medium-weight cadaver at radiation settings < 1 mSv and either 5 or 7.5 mA, both sensitivity and specificity were significantly lower in the low- and high-weight cadavers. However, at radiation settings of ≥ 15 mA, differences in sensitivity and specificity were not significant between groups [47]. Poletti et al. prospectively compared low- versus standarddose CT (30 vs. 180 mA) in 125 patients with renal colic. Estimated ERD in standard versus LDCT for men were 9.6 vs. 1.6 mSv in men and 12.6 vs. 2.1 mSv in women. In patients


with a BMI < 30 kg/m2, the sensitivity and specificity for detection of ureteral stones was comparable between the standard and LDCT group (95 vs. 97%, respectively). However, ureteral calculi < 3 had a lower sensitivity of 86% in the LDCT group versus 100% for stones > 3 mm. LDCT was less precise for stone size determination, where ureteral stone size varied up to ± 20% [39]. Similarly, Hamm et al. advocated the standard CT protocol in patients with BMI > 31 kg/m2 to improve detection of stones. Excellent sensitivity and specificity of a LDCT has been reported in 109 patients with ureteral stones detection, which were confirmed by retrograde pyelography and/or clinical follow-up and US. Low-dose parameters (70 mA) were associated with more than 50% reduction in ERD compared with their standard protocol (129 mA). Sensitivity and specificity for diagnosis of stones was 96% and 97% with a 99% positive and 90% negative predictive value [43]. Magnetic Resonance Imaging (MRI) Despite MRI not using ionizing radiation, it has a limited role in the diagnosis of nephrolithiasis due to its prohibitive cost, limited accessibility, prolonged time of study, and inability to directly visualize stones, which merely appear as filling defects. However, signs of obstruction can be well visualized such as dilatation of the upper urinary tract and perirenal fluid collection with a sensitivity and specificity of 93 and 95%, respectively. Hence, MRI can be used in children and pregnant women to avoid any radiation exposure. Newer techniques such as the HASTE MRI [MRI after “half Fourier single-shot turbo spin-echo (HASTE) protocol”] coupled with the capture of detailed anatomic imaging display lead to improved visualization of intraluminal concretions [48]. New Imaging Technology Micro-CT is currently used for research purposes only and still has no role in clinical practice, but it looks like a promising modern technology. It is suitable for analysis of stone composition, where the calculus is rotated more than 180° in a continuous X-ray beam in steps of 0.4°. Therefore, more than 500 images can be generated to determine the morphology and composition of urinary stones. Dual-energy CT uses two different detectors with different voltages rotating around the patient to determine the actual stone composition. The concerned stones are then shown in the usual sectional images in assorted colors, depending on the composition. This method seems promising for planning management, but is relatively expensive and not currently available in many centers [49]. Uro-Dyna-CT is a ceiling mounted C-arm with 5 degrees of freedom and a digital flat detector, which with the help of pulsed fluoroscopy can reconstruct three-dimensional (3D)

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images. These images can be used intraoperatively to allow 3D puncture and access to the kidney. Corresponding DynaCT low-dose protocols have also been developed, where an effective dose of 0.33 mSv has been estimated [50]. Digital tomosynthesis (DT) is a relatively new tool for the diagnosis and follow-up of kidney stones. This technique enables the reconstruction of coronal images from two digital overviews and a digital sweep. High-resolution images can be reconstructed using appropriate image processing software in any penetration depth. This method has better detection of kidney stones than the traditional tomography, especially since it requires only one sweep of the X-ray tube with consequent reduction of radiation exposure. Sensitivities are 64 and 76% for 2–5-mm and > 5-mm stones, respectively [51]. The radiation dose of DT is slightly higher than digital radiography, but lower than CT or even low-dose CT. IVUs with DT had significantly higher diagnostic quality than conventional IVUs (95.5 vs. 46.5%) [52]. Organ-specific radiation doses of DT were significantly lower than NCCT, and the effective dose of DT was significantly lower than NCCT (0.87 vs. 3.04 mSv), a dose corresponding to a fifth of NCCT or IVU studies [28, 53]. Therefore, DT could play a role in the future during postoperative follow-up of patients with nephrolithiasis. Radiation Exposure in Evaluation of Urolithiasis Katz and colleagues have assessed the impact of repetitive CT scans for suspected renal colic on radiation dose. The doselength product (DLP) was estimated for 15 randomly chosen single and multidetector CT scanners using manufacturer’s software, and the mean DLPs for single and multidetector CT were computed and converted to ERD. The mean effective doses for a single study were 6.5 and 8.5 mSv for single and multidetector CT, respectively. Only 76 patients (4%) underwent ≥ 3 examinations and had a known history of nephrolithiasis, with estimated ERD of 19.5–153.7 mSv [54]. This study demonstrated that patients presenting with acute flank pain and had a history of nephrolithiasis were at increased risk of higher cumulative effective radiation doses from repeated CT scans. Another study evaluated patients with a single complete stone episode from the time of diagnosis to stone-free status. KUB and IVU were initially performed while CT was performed in select cases. The median ERD was significantly lower than studies involving higher utilization of CT (5.3 vs. 14.46 mSv) [55]. This study was performed in a center with less accessible CT, emphasizing the impact of institutional factors on cumulative radiation doses. Cumulative radiation exposure in patients with nephrolithiasis has been evaluated by several studies. In a multicenter retrospective study, all imaging studies which have been performed for 108 patients presenting with primary acute stone episodes within 1 year were assessed. The estimated total ERD was 1.7 mSv for a

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two-film KUB, 2.5 mSv for six-film IVU, and 10 mSv for abdominal/pelvic CT [13]. The median estimated radiation dose per patient was 29.7 mSv, while 20% of patients exceeded the ICRP safety threshold of 50 mSv for a single year [12]. A recent study calculated the ERD of CT from the reported DLP rather than using reported estimated values in patients with urolithiasis within 2 years from diagnosis. The ERD of each CT scan was calculated by multiplying the DLP (mSv/ cm) by a conversion factor of 0.015. The average calculated ERD per CT scan was 23.16 (4.94–72.77) mSv, which was significantly higher than an average ERD per fluoroscopic examination of 2.21 (0.72–4.77) mSv [14]. Of interest, the average ERD per patient significantly decreased from 29.29 (1.7–77.27) mSv in the first year of follow-up to 8.04 (1.4– 24.72) mSv in the second year. This was due to the significantly fewer KUBs, CTs, IVUs, and fluoroscopic studies and significantly higher number of US during the second year of follow-up [14]. While 18 patients (17.3%) exceeded the ICRP safety threshold of 50-mSv dose during the first year of follow-up, none of the patients exceeded this threshold during the second year. Compared to patients who received mean ERD < 50 mSv, patients who exceeded the safe threshold had significantly more CT scans (0.62 vs. 0.35 CT scans/patient) and significantly fewer US studies (0.7 vs. 1.1 US/patient) [14]. This study highlights the benefits of using US instead of CT scans in the follow-up of patients undergoing treatment for nephrolithiasis. Similarly, Kaynar et al. calculated the ERD during 1 year after SWL in 129 patients, including 44 with kidney stones, 41 with ureteral stones, and 44 with multiple stones location. The mean total ERD values were 15.91 (5.10–27.60) mSv, 13.32 (5.10–24.70) mSv, and 27.02 (9.41–54.85) mSv for the three groups, respectively. Patients with either renal or ureteral stones were comparable in terms of the ERD dose, but both had significantly lower EDR than those with the multiple stone locations [15]. Therefore, patients with multiple stone locations are vulnerable to higher exposure to ionizing radiation. In 233 patients undergoing ureteroscopy (URS) or PCNL for management of upper urinary tract calculi, a mean of 1.58 CTs were performed per patient. Nearly 39% of patients received at least two CT scans perioperatively (≤ 90 days), with an average of 2.49 CTs/patient, resulting in 49.8 mSv of radiation exposure. Patients undergoing URS had significantly more CTs than those undergoing PCNL, but the median radiation exposure was higher in PCNL patients (43.3 vs. 27.6 mGy) due to the use of fluoroscopy for percutaneous access [56]. To minimize radiation exposure for patients with nephrolithiasis, the AUA guidelines recommend low-dose CT scan for patients with BMI ≤ 30 kg/m2, while standarddose CT scan is recommended for patients with BMI > 30 kg/ m2 when patients present with acute renal colic. During


follow-up of radiopaque stones, US and conventional radiography are recommended to monitor stone passage and assess postoperative stone-free status [57••]. Finally, the AUA recommends obtaining renal US post-URS to rule out silent strictures, while it recommends obtaining CT urography in symptomatic patients post-URS to rule out strictures [57••]. Radiation Exposure During Management of Urolithiasis Urologists depend on fluoroscopic guidance for different endourological techniques to obtain real-time X-ray imaging during the procedure. Urologists need to follow As Low As Reasonably Achievable or ALARA principles of minimizing time, maximizing distance, and always using shields. Intraoperative fluoroscopy is usually associated with small but measurable amounts of radiation exposure to patients and operating room personnel. In a review of 50 articles regarding radiation exposure during management of urolithiasis, Chen et al. found that patients are exposed to a significant amount of radiation during their first time acute stone episode, most of it coming from CT. However, patients undergoing PCNL were exposed to a greater amount of radiation than they received from CT scans, while URS exposed them to approximately the same amount of radiation as KUB [58••]. Risk factors for increased exposure during PCNL included obesity, larger stone burden, and multiple tracts, while obesity and ureteral dilation were associated with increased exposure during URS. These studies did not characterize the amount of radiation exposure during SWL. Use of US and LDCT protocols were the main factors associated with reduced radiation exposures. Pitter et al. used thermo-luminescent dosimeters at the ring finger and another at the surgeon’s forehead to measure representative doses to the lens of the eye and thyroid. For each intervention, the following average values were recorded at the forehead and finger, respectively: ureteral stent placement, 0.04 and 0.13 mSv; percutaneous stent change, 0.03 and 0.20 mSv; PCNL, 0.18 and 4.36 mSv; and URS, 0.1 and 0.15 mSv [59]. Ureteral stent placement without fluoroscopic guidance is feasible with comparable efficacy and complication rates with conventional stent placement. All stents were placed successfully without fluoroscopic guidance. Placement was achieved in 76% of the fluoro-less group versus 64% of the traditional group [60]. Radiation Exposure During URS The intraoperative ERD for patients during URS ranges from 0.67 to 2.23 mSv, depending on stone location, type of URS (semi-rigid versus flexible), and type of stone removal (simple extraction versus intracorporeal lithotripsy) [61]. Patient’s radiation exposure during URS is comparable to that obtained from KUB or LDCT for diagnosis of nephrolithiasis. Lipkin


et al. measured the ERD rate during simulated URS using a validated anthropomorphic male phantom placed on a fluoroscopy table. The mean ERD rate was 0.024 mSv/s, with a median fluoroscopy time (FT) of 46.95 s and a median ERD of 1.13 mSv. Non-obese males were exposed to a median of 1.13 mSv during URS. The mean absorbed dose for skin entrance was 0.3286 mGy/s, the highest absorbed dose rate, followed by 0.1882 ± mGy/s for the small intestine [62]. Keeping track of FT similar to keeping track of warm ischemia time during partial nephrectomy is another important measure of reducing radiation exposure to patients. In one study, mean FT for unilateral URS decreased by 24% after surgeons received feedback [63]. Other studies reported significant independent predictors of prolonged FT during URS, including surgeon behavior, postgraduate trainees, male gender, balloon dilation, longer duration of surgery, residual stones at the end of the procedure, and the use of access sheaths [64, 65]. Several investigators have come up with cost-effective maneuvers in reducing radiation exposure during URS. Using laser-guided fluoroscopy unit, Greene et al. reported 82% reduction in FT (from a mean of 86.1 to 15.5 s) without altering patient outcomes. Operative time and complications were comparable between groups [66]. Another cost-effective maneuver is to use pulsed fluoroscopy. Since standard fluoroscopy (SF) operates at a rate of 30 frames per seconds (fps), the effect of using pulsed fluoroscopy (PF) at a rate of 4 fps has been examined in reducing FT during URS. Compared with SF, use of PF in URS significantly decreased FT by 60% (109.1 vs. 44.1 s) [67]. Recently, 1 fps was described during URS. The authors demonstrated that there was a significant decrease in the median FT (77 vs. 16 s; p < 0.001) [68]. This translated to 64% reduction in the monthly surgeon radiation exposure. Therefore, FT during URS could be minimized by using a laser-guided C-arm, pulse fluoroscopy, a dedicated technician, visual stent placement, and tactile feedback for guide wire placement [58••, 67]. Radiation Exposure During PCNL Fluoroscopically guided PCNL is associated with the highest radiation exposure among all endourological procedures [69]. Factors associated with increased ERD during PCNL are increased BMI, higher stone burden, non-branched stone configuration, and a greater number of percutaneous access tracts [70]. The authors found that obese patients with a BMI of 30–39.9 kg/m2 had more than twofold increase in the mean adjusted ERD, whereas patients with higher BMI had a greater than threefold increase when compared with normal-weight patients (6.49 and 9.13 mSv, respectively, vs. 2.66 mSv). Lipkin et al. reported a higher ERD rate for left-sided PCNLs compared with right-sided PCNLs (0.021 vs. 0.014 mSv). The skin was exposed to the greatest amount of radiation, 0.24–0.26 mGy/s [71]. Moreover, radiation

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exposure significantly decreased when using air rather than contrast during retrograde pyelography, where the mean adjusted ERD decreased by nearly twofold, from 7.67 to 4.45 mSv [72]. This is because the air has a lower density and requires less radiation to penetrate and produce an image. Surgeon behavior and changes in fluoroscopy practice after being informed about their FT also impact radiation exposure. Surgeons reduced 55% of their median FT after being informed about their fluoroscopy usage [73]. PF at 4 fps during PCNL was associated with a 65% reduction in FT compared with those performed using SF at 30 fps [67]. Blair et al. reported 81% reduction in FT during PCNLs by using PF at 1 fps, visual and tactile cues, fixed lower milliampere and kilovoltage, a designated fluoroscopy technician, and a laserguided C-arm [74]. Furthermore, endoscopic-guided percutaneous renal access has been described to significantly reduce FT during PCNL [75, 76] Moreover, PCNL in patients with pre-formed percutaneous renal access has been associated with significantly less FT since obtaining percutaneous renal access contributes to 36% of FT during PCNL [77]. Finally, ultrasound-guided PCNL is feasible, safe, and efficacious for the treatment of nephrolithiasis in children, providing the advantages of lower radiation exposure. Radiation Exposure During SWL SWL necessitates the use of fluoroscopy or US for stone localization and targeting of shockwaves. The ERD to patients during SWL using fluoroscopy is typically < 2 mSv [78, 79]. Radiation exposure during SWL increases with stone burden, which requires longer treatment and more X-rays. A typical SWL procedure comprises FT of about 2.6–3.4 min and 4–26 spot films, resulting in an average dose of 1.6 mSv per patient [79]. A recent study demonstrated that SWL was significantly associated with a higher ERD than URS for management of renal stones, which can be significantly predicted by BMI and stone size. However, for ureteral stones, both modalities were associated with similar levels of radiation [80]. This could be considered for recurrent stone-formers, for whom cumulative exposures may become significant. Experienced radiological technologists have been shown to be associated with significantly lower FT and higher fragmentation rates [81]. Lifetime Radiation Exposure in Recurrent Stone-Formers All regulatory rules that reduce radiation exposure to the patient will also lead to reduction in radiation exposure to health care personnel, but the reverse is not true. This is because operating room personnel usually use protective measures such as lead aprons, thyroid shields, and leadimpregnated goggles and gloves, which do not reduce

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radiation exposure to the patient. Unfortunately, patient radiation protection has not received as much attention as urologists. Most relevant publications dealing with radiation safety in urology focused on radiation risks to the surgeon and operating room personnel, without estimating radiation doses to patients. The argument that surgeons and other health care providers work with radiation for all their careers, whereas patients undergo radiological procedures only a few times during lifetime, is not acceptable anymore. This is because the protected operating room personnel face only scattered radiation, which represents less than 1% of the radiation dose falling on the patient. This translates to about 0.1% of the radiation dose received by the patient per procedure. The average annual worldwide dose for occupational exposure in medicine is 0.5 mSv/year [78]. Consequently, for a person working for an average of 40 years, the total dose may not exceed 20 mSv over his/ her career. Furthermore, survey of non-radiologists and non-cardiologists conducted in over 30 developing countries confirmed the absence of patient dose monitoring in almost 90% of cases [82]. Many patients with nephrolithiasis may receive radiation doses that exceed the typical dose received by the surgeon and operating room personnel during their entire career. Therefore, patient dose estimation is needed and manufacturers should develop different modes to indicate patient dose indices which can be transferred to hospital networks. During the first year of follow-up, radiological studies performed in an acute stone episode may include one or two KUBs, an intravenous urography, and one or two CT scans of the abdomen and pelvis reaching a total ERD of 20–50 mSv [13]. Moreover, up to 20% of patients may be exposed to more than the “safe” threshold of exposure of 50 mSv during diagnosis and first year of follow-up [13, 14•]. Increasing use of CT scans imparts higher doses of ionizing radiation to patients with urinary calculi, and many patients may be subjected to relatively higher doses during the acute stone event and its management [70]. Such exposure levels do not include treatment-related radiation from fluoroscopy. Currently, many fluoroscopic procedures are interventional and impart higher radiation doses to patients. These fluoroscopic-guided procedures may be diagnostic, including retrograde/antegrade urography and insertion or change of ureteral stents, or therapeutic, including SWL, URS, or PCNL. The fluoroscopy machine captures realtime images of the contrast medium during a given procedure to study the anatomical details or the dynamics of urine drainage. Therefore, fluoroscopy equipment can deliver even higher radiation doses in a short time, making FTalone a poor indicator of the actual ERD. Moreover, a nephrostomy tube placement may be required in some patients with obstructive uropathies, which may require an average of 10–15 min (1– 56) of fluoroscopy, resulting in relatively high doses


of radiation [83, 84]. Typical ERD from a nephrostomy procedure is 7.7 (3.4–15) mSv [78, 79]. In addition, repeated examinations may be necessary in some patients to confirm proper nephrostomy tube placement. It should be considered that different tissues and organs have different radiosensitivities and females are more radiosensitive than males to radiation-induced cancers. Similarly, children and young patients have increased radiosensitivity compared to older patients. Therefore, it is necessary for the urologist to weigh the expected clinical benefits to the patient from imaging studies or a given urological procedure requiring fluoroscopy against radiation risks involved. The American Urological Association proposed an algorithm for imaging patients with acute stone episodes in the emergency room [57••]. It recommends low-dose CT for patients with BMI of ≤ 30 kg/m2 to limit the potential long-term adverse events of ionizing radiation. The sensitivity and specificity of low-dose CT for detecting ureteral stones in these patients is maintained higher than 90%, in contrast to those with a BMI > 30 kg/m2. Therefore, for patients with BMI > 30 kg/m2, standard-dose CT scan is recommended. However, guidelines may impact clinical decision making, but will likely not reduce CT use, where there is a lack of compliance of current imaging practices to recently published guidelines. For example, initial US is recommended for children with suspected kidney stones, but only 24% of children in the USA between 2003 and 2011 were found to have US versus 63% who underwent CTs as the initial imaging study [85]. The BEIR VII committee had developed a lifetime risk model, confirming a relationship of linear dose–response in humans between ionizing radiation exposure and the emergence of radiation-induced solid cancers. This model predicts the development of solid cancer or leukemia in nearly 1/100 people from a dose of 100 mSv above background versus 42/100 people from other causes [8]. The question is the impact of the dose rate on development of solid cancers. Is the risk of developing cancers from a 100 mSv exposure over a 5-year period of interventional procedures different from 20 CT scans over a 10-year period? Currently, no sufficient data is available to answer this question. Sodickson et al. reviewed 31,462 patients who underwent 190,712 diagnostic CT scans over a 22-year period and estimated each patient’s cumulative radiation exposure. Thirtythree percent of patients underwent ≥ 5 CT scans in their lifetime, while 5% underwent 22–132 CT scans. Fifteen percent received estimated cumulative effective doses greater than 100 mSv, while 4% received 250–1375 mSv. The mean and maximum values were 0.3% and 12% for lifetime attributable risk for cancer and 0.2% and 6.8% of cancer mortality, respectively. Radiation exposure from CT scans was responsible for 0.7% of total expected baseline cancer incidence and 1% of overall cancer mortality [86].


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Conclusions

5.

There is an increasing concern about radiation exposure and its cumulative hazards during diagnosis, treatment, and follow-up of patients with nephrolithiasis, especially for patients with recurrent stones. Urologists should be aware of the risks of ionizing radiation and strive to minimize radiation exposure, especially in the most susceptible populations, through selection of the appropriate imaging modality. They should adhere, as much as possible, to the ALARA principles of minimizing time, maximizing distance, and always wearing shields. Although radiation exposure of a single radiograph is relatively low, accumulated doses from repeated studies for recurrent stone-formers increase the risk of radiation-induced hazards. NCCT was the gold standard. Currently, for patients with BMI ≤ 30 kg/m2, the recommended imaging modality for acute renal colic is low-dose CT scan according to the imaging guidelines of the American Urological Association. It also recommends the use of KUB with US to follow patients with radiopaque stones. Only in symptomatic patients postureteroscopy a CT urogram is recommended to evaluate for strictures. Intraoperative maneuvers that result in significant reductions in radiation exposure include the use of a laserguided C-arm, a dedicated experienced radiological technologist, and pulse fluoroscopy at 1–4 frames per second. Future studies need to quantify lifetime radiation exposure of patients with recurrent nephrolithiasis.

6.

Compliance with Ethical Standards Conflict of Interest Mohamed A. Elkoushy and Sero Andonian each declare no potential conflicts of interest. Human and Animal Rights and Informed Consent This article does not contain any studies with human or animal subjects performed by any of the authors.

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16.

17.

18.

19.

References Papers of particular interest, published recently, have been highlighted as: • Of importance •• Of major importance 1.

2. 3.

4.

Stamatelou KK, Francis ME, Jones CA, et al. Time trends in reported prevalence of kidney stones in the United States: 1976– 1994. Kidney Int. 2003;63:1817–23. Scales CD Jr, Smith AC, Hanley JM, et al. Prevalence of kidney stones in the United States. Eur Urol. 2012;62:160–5. Cho JS, Fulgham PF, Clark AR, et al. Follow-up imaging after urologic imaging studies: comparison of radiologists’ recommendation and urologists’ practice. J Urol. 2010;184:254. Brisbane W, Bailey MR, Sorensen MW. An overview of kidney stone imaging techniques. Nat Rev Urol. 2016;13(11):654–62.

20. 21.

22.

23.

24.

25.•

Fwu CW, Eggers PW, Kimmel PL, et al. Emergency department visits, use of imaging, and drugs for urolithiasis have increased in the United States. Kidney Int. 2013;83:479–86. Brenner DJ, Hall EJ. Computed tomography: an increasing source of radiation exposure. N Engl J Med. 2007;357:2277–84. National Research Council. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. Report in Brief. Washington, DC: National Academies Press; 2005. Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation NRC. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. Washington, DC: National Academies Press; 2012. Available at: http://www. nap.edu/catalog/11340.html, accessed at January 2017. Pierce DA, Preston DL. Radiation-related cancer risks at low doses among atomic bomb survivors. Radiat Res. 2000;154:178–86. Preston DL, Pierce DA, Shimizu Y, et al. Effect of recent changes in atomic bomb survivor dosimetry on cancer mortality risk estimates. Radiat Res. 2004;162:377–89. Preston DL, Ron E, Tokuoka S, et al. Solid cancer incidence in atomic bomb survivors: 1958–1998. Rad Res. 2007;168:1–64. ICRP Publication 60. Recommendations of the International Commission on Radiological Protection, 60. Ann ICRP. 1990;1991(21):1–3. Ferrandino MN, Bagrodia A, Pierre SA, et al. Radiation exposure in the acute and short-term management of urolithiasis at 2 academic centers. J Urol. 2009;181:668–73. Fahmy NM, Elkoushy MA, Andonian S. Effective radiation exposure in evaluation and follow-up of patients with urolithiasis. Urology. 2012;79:43–7. The effective radiation dose associated with the evaluation and follow-up of patients with urolithiasis was calculated and not estimated, as mostly reported. In addition, it gave beyond-single-year follow-up of these patients Kaynar M, Tekinarslan E, Keskin S, et al. Effective radiation exposure evaluation during a one year follow-up of urolithiasis patients after extracorporeal shock wave lithotripsy. Cent Eur J Urol. 2015;68:348–52. Pierce DA, Shimizu Y, Preston DL, et al. Studies of the mortality of atomic bomb survivors. Report 12, part I. Cancer: 1950–1990. Radiat Res. 1996;146:1–27. Brenner DJ, Elliston C, Hall E, et al. Estimated risks of radiationinduced fatal cancer from pediatric CT. AJR Am J Roentgenol. 2001;176:289–96. Cardis E, Vrijheid M, Blettner M, et al. The 15-country collaborative study of cancer risk among radiation workers in the nuclear industry: estimates of radiation-related cancer risks. Radiat Res. 2007;167:396–416. Mettler FA Jr, Huda W, Yoshizumi TT, Mahesh M. Effective doses in radiology and diagnostic nuclear medicine: a catalog. Radiology. 2008;248(1):254–63. Andonian S, Atalla MA. Radiation safety in urology. AUA Update Ser. 2009, Lesson 26, 28:237–247. Catalano O, Nunziata A, Altei F, et al. Suspected ureteral colic: primary helical CT versus selective helical CT after unenhanced radiography and sonography. AJR Am J Roentgenol. 2002;178:379–87. Heidenreich A, Desgranschamps F, Terrier F. Modern approach of diagnosis and management of acute flank pain: review of all imaging modalities. Eur Urol. 2002;41:351–62. Katz D, McGahan JP, Gerscovich EO, et al. Correlation of ureteral stone measurements by CT and plain film radiography: utility of the KUB. J Endourol. 2003;17:847–50. Narepalem N, Sundaram CP, Boridy IC, et al. Comparison of helical computerized tomography and plain radiography for estimating urinary stone size. J Urol. 2002;167:1235–8. Neisius A, Wang AJ, Wang C, et al. Radiation exposure in urology: a genito-urinary catalog for diagnostic imaging. J Urol. 2013;190(o):2117–23. Using anthropomorphic male phantom

85

26.

27.

28.•

29.

30. 31.

32.

33.

34.

35.

36. 37.

38.

39.

40.••

41.


Page 10 of 11 validated for human organ dosimetry measurements, the authors confirmed the validity of calculated effective dose derived from the dose-length product to estimate patient radiation exposure, while the effective dose varies considerable for different urological CT studies. Ripolles T, Agramunt M, Errando J, et al. Suspected ureteral colic: plain film and sonography vs. unenhanced helical CT. A prospective study of 66 patients. Eur Radiol. 2004;14:129–36. Goldwasser B, Cohan RH, Dunnick NR, et al. Role of linear tomography in evaluation of patients with nephrolithiasis. Urology. 1989;33:253–6. Astroza GM, Neisius A, Wang AJ, et al. Radiation exposure in the follow-up of patients with urolithiasis comparing digital tomosynthesis, non-contrast CT, standard KUB, and IVU. J Endourol. 2013;27(10):1187–91. While IVU or KUB with tomograms exposes patients to more ionizing radiation than lowdose CT protocol, digital tomosynthesis, however, has a lower effective dose than the different imaging modalities. Therefore, it can play a significant role in surveillance of patients with urolithiasis Muller M, Heicappell R, Steiner U, et al. The average dose-area product at intravenous urography in 205 adults. Br J Radiol. 1998;71(842):210–2. Erwin BC, Carroll BA, Summer FG. Re: US in the evaluation of acute flank pain. Radiology. 1885;157(2):554. Tzou DT, Usawachintachit M, Taguchi K, Chi T. Ultrasound use in urinary stones: adapting old technology for a modern-day disease. J Endourol. 2017;31(S1):S89–94. Smith-Bindman R, Aubin C, Bailitz J, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. N Engl J Med. 2014;371(12):1100–10. Abdel-Gawad M, Kadasne RD, Elsobkr E, et al. A prospective comparative study of color Doppler ultrasound with twinkling and noncontrast computerized tomography in the evaluation of acute renal colic. J Urol. 2016;196:1–6. Keilar AZ, Shabana W, Vakili M, et al. Prospective evaluation of Doppler sonography to detect the twinkling artifact versus unenhanced computed tomography for identifying urinary tract calculi. J Ultrasound Med. 2012;31:1619–25. Dunmire B, Harper JD, Cunitz BW, et al. Use of the acoustic shadow width to determine kidney stone size with ultrasound. J Urol. 2016;195:171–7. May PC, Haider Y, Dunmire B, et al. Stone-mode ultrasound for determining renal stone size. J Endourol. 2016;30:958–62. Cabrera F, Preminger GM, Lipkin ME. As low as reasonably achievable: methods for reducing radiation exposure during the management of renal and ureteral stones. Indian J Urol. 2014;30:55–9. Kluner C, Hein PA, Gralla O, et al. Does ultra-low-dose CT with a radiation dose equivalent to that of KUB suffice to detect renal and ureteral calculi? J Comput Assist Tomogr. 2006;30:44–50. Poletti PA, Platon A, Rutschmann OT, et al. Low-dose versus standard-dose CT protocol in patients with clinically suspected renal colic. AJR Am J Roentgenol. 2007;188:927–33. Pooler BD, Lubner MG, Kim DH, et al. Prospective trial of the detection of urolithiasis on ultralow dose (sub mSv) noncontrast computerized tomography: direct comparison against routine low dose reference standard. J Urol. 2014;192:1433–9. Using advanced ultra-low-dose refined reconstruction algorithms would help in reducing NCCT radiation dose to less than that of a typical 2-KUBs, without severely affecting its diagnostic accuracy to detect clinically significant calculi. Glazer DI, Maturen KE, Cohan RH, et al. Assessment of 1 mSv urinary tract stone CT with model-based iterative reconstruction. Am J Roentgenol. 2014;203:1230–5.

42.

43.

44.

45.

46.

47.

48.

49.

50.

51.

52.

53.

54.

55. 56.

57.••

58.••

Jellison FC, Smith JC, Heldt JP, et al. Effect of low dose radiation computerized tomography protocols on distal ureteral calculus detection. J Urol. 2009;182(6):2762–7. Hamm M, Knopfle E, Wartenberg S, et al. Low dose unenhanced helical computerized tomography for the evaluation of acute flank pain. J Urol. 2002;167:1687–91. Katz DS, Venkataramanan N, Napel S, et al. Can low-dose unenhanced multidetector CT be used for routine evaluation of suspected renal colic? AJR Am J Roentgenol. 2003b;180:313–5. Ciaschini MW, Remer EM, Baker ME, et al. Urinary calculi: radiation dose reduction of 50% and 75% at CT—effect on sensitivity. Radiology. 2009;251(1):105–11. Kim BS, Hwang IK, Choi YW, et al. Low-dose and standard-dose unenhanced helical computed tomography for the assessment of acute renal colic: prospective comparative study. Acta Radiol. 2005;46:756–63. Heldt JP, Smith JC, Anderson KM, et al. Ureteral calculi detection using low dose computerized tomography protocols is compromised in overweight and underweight patients. J Urol. 2012;188:124–9. Mullins JK, Semins MJ, Hyams ES, et al. Half-Fourier single-shot turbo-spin-magnetic resonance urography for the evaluation of suspected renal colic in pregnancy. Urology. 2012;79(6):1252–5. Qu M, Ramirez-Giraldo JC, Leng S, et al. Dual-energy dual-source CT with additional spectral filtration can improve the differentiation of non-uric acid renal stones: an ex vivo phantom study. AJR Am J Roentgenol. 2011;196(6):1279–87. Ritter M, Rassweiler MC, Michel MS. The Uro Dyna-CT allows three-dimensional planned laser-guided complex punctures. Eur Urol. 2015;68(5):880–4. Mermuys K, De Geeter F, Bacher K, et al. Digital tomosynthesis in the detection of urolithiasis: diagnostic performance and dosimetry compared with digital radiography with MDCT as the reference standard. Am J Roentgenol. 2010;195:161–7. Wells IT, Raju VM, Rowberry BK, et al. Digital tomosynthesis—a new lease of life for the intravenous urogram? Br J Radiol. 2011;84(1001):464–8. Neisius A, Astroza GM, Wang C, et al. Digital tomosynthesis: a new technique for imaging nephrolithiasis. Specific organ doses and effective doses with the renal stone protocol noncontrast computed tomography. Urology. 2014;83(2):282–7. Katz SI, Saluja S, Brink JA, et al. Radiation dose associated with unenhanced CT for suspected renal colic: impact of repetitive studies. AJR Am J Roentgenol. 2006;186:1120–4. John BS, Patel U, Anson K. What radiation exposure can a patient expect during a single stone episode? J Endourol. 2008;22:429–2. Jamal JE, Armenakas NA, Sosa RE, et al. Perioperative patient radiation exposure in the endoscopic removal of upper urinary tract calculi. J Endourol. 2011;25(11):1747–51. Fulgham PF, Assimos DG, Pearle MS, et al. Clinical effectiveness protocols for imaging in the management of ureteral calculous disease: AUA technology assessment. J Urol. 2013;189(4):1203–13. This review article addresses the optimal use of imaging studies in the management of patients with suspected or documented ureteral calculi, considering the clinical and cost-effectiveness of various imaging modalities and associated risk of radiation exposure Chen TT, Wang C, Ferrandino MN, et al. Radiation exposure during the evaluation and management of nephrolithiasis. J Urol. 2015;194:878–85. This review article described increased trends in the use of CT, risks associated with low-dose radiation exposure, exposure from different diagnostic imaging studies and discussed methods to reduce radiation exposure for patients with nephrolithiasis.

Curr Urol Rep (2017) 18:85 59.

Ritter M, Krombach P, Martinschek A, et al. Radiation exposure during endourologic procedures using over-the-table fluoroscopy sources. J Endourol. 2012;26(1):47–51. 60. Brisbane W, Smith D, Schlaifer A, et al. Fluoro-less ureteral stent placement following uncomplicated ureteroscopic stone removal: a feasibility study. Urology. 2012;80:766–70. 61. Zöller G, Virsik-Köpp P, Vowinkel C. Patient radiation exposure during ureteroscopic stone extraction. Urologe A. 2013;52(1):60–4. 62. Lipkin ME, Wang AJ, Toncheva G, et al. Determination of patient radiation dose during ureteroscopic treatment of urolithiasis using a validated model. J Urol. 2012;187(3):920–4. 63. Ngo TC, Macleod LC, Rosenstein DI, et al. Tracking intraoperative fluoroscopy utilization reduces radiation exposure during ureteroscopy. J Endourol. 2011;25(5):763–7. 64. Elkoushy MA, Andonian S. Variations among urology trainees in their use of fluoroscopy during ureteroscopy. J Endourol. 2012;27(1):19–23. 65. Violette PD, Szymanski KM, Anidjar M, Andonian S. Factors determining fluoroscopy time during ureteroscopy. J Endourol. 2011;25(12):1837–40. 66. Greene DJ, Tenggadjaja CF, Bowman RJ, et al. Comparison of a reduced radiation fluoroscopy protocol to conventional fluoroscopy during uncomplicated ureteroscopy. Urology. 2011;78:286–90. 67. Elkoushy MA, Shahrour W, Andonian S. Pulsed fluoroscopy in ureteroscopy and percutaneous nephrolithotomy. Urology. 2012;79(6):1230–5. 68. Yecies TS, Fombona A, Semins MJ. Single pulse-per-second setting reduces fluoroscopy time during ureteroscopy. Urology. 2017;103:63–7. 69. Hellawell GO, Mutch SJ, Thevendran E, et al. Radiation exposure and the urologist: what are the risks? J Urol. 2005;174:948–52. 70. Mancini JG, Raymundo EM, Lipkin M, et al. Factors affecting patient radiation exposure during percutaneous nephrolithotomy. J Urol. 2010;184(6):2373–7. 71. Lipkin ME, Mancini JG, Toncheva T, et al. Organ-specific radiation dose rates and effective dose rates during percutaneous nephrolithotomy. J Endourol. 2012;26(5):439–43. 72. Lipkin ME, Mancini JG, Zilberman DE, et al. Reduced radiation exposure with the use of an air retrograde pyelogram during fluoroscopic access for percutaneous nephrolithotomy. J Endourol. 2011;25(4):563–7.

Page 11 of 11 85 73.

Ritter M, Siegel F, Krombach P, et al. Influence of surgeon’s experience on fluoroscopy time during endourological interventions. World J Urol. 2013;31(1):183–7. 74. Blair B, Huang G, Arnold D, et al. Reduced fluoroscopy protocol for percutaneous nephrostolithotomy: feasibility, outcomes and effects on fluoroscopy time. J Urol. 2013;190:2112–6. 75. Isac W, Rizkala E, Liu X, et al. Endoscopic-guided versus fluoroscopic-guided renal access for percutaneous nephrolithotomy: a comparative analysis. Urology. 2013;81:251–6. 76. Lantz AG, O’Malley P, Ordon M, et al. Assessing radiation exposure during endoscopic-guided percutaneous nephrolithotomy. Can Urol Assoc J. 2014;8(9e10):347–51. 77. Noureldin YA, Elkoushy MA, Andonian S. Does the presence of a percutaneous renal access influence fluoroscopy time during percutaneous nephrolithotomy? Asian J Urol. 2015;2(4):220–3. 78. UNSCEAR 2010. Sources and effects of ionizing radiation. UNSCEAR 2008 Report, United Nations, New York. 79. Sandilos P, Tsalafoutos I, Koutsokalis G, et al. Radiation doses to patients from extracorporeal shockwave lithotripsy. Health Phys. 2006;90:583–7. 80. Rebuck DA, Coleman S, Chen JF, et al. Extracorporeal shockwave lithotripsy versus ureteroscopy: a comparison of intraoperative radiation exposure during the management of nephrolithiasis. J Endourol. 2012 Jun;26(6):597–601. 81. Elkoushy MA, Morehouse DD, Anidjar M, et al. Impact of radiological technologists on the outcome of shock wave lithotripsy. Urology. 2012;79(4):777–80. 82. IAEA, 2010. Radiation protection of patients. http://rpop.iaea.org, accessed 14.2.2011. 83. NCRP. Radiation protection for procedures performed outside the radiology department. NCRP Report 2000; 133. The National Council on Radiation Protection and Measurements, Bethesda, USA. 84. Miller DL, Balter S, Cole PE, et al. Radiation doses in interventional radiology procedures: the RAD-IR study part I. Overall measures of dose. J Vasc Interv Radiol. 2003;14:711–27. 85. Tasian GE, Pulido JE, Keren R, et al. Use of and regional variation in initial CT imaging for kidney stones. Pediatrics. 2014;134(5): 909–15. 86. Sodickson A, Baeyens PF, Andriole KP, et al. Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults. Radiology. 2009;251(1):176–84.