Review Article. Radiation Exposure during the Evaluation and Management of Nephrolithiasis

Transcription

1 Review Article Radiation Exposure during the Evaluation and Management of Nephrolithiasis Tony T. Chen, Chu Wang, Michael N. Ferrandino, Charles D. Scales, Terry T. Yoshizumi, Glenn M. Preminger and Michael E. Lipkin* From the School of Medicine (TTC), Division of Radiation Safety (CW, TTY), Division of Urology, Department of Surgery (MNF, CDS, GMP, MEL) and Departments of Radiology (TTY) and Radiation Oncology (TTY), Duke University Medical Center, Durham, North Carolina Abbreviations and Acronyms ALARA ¼ as low as reasonably achievable BMI ¼ body mass index CT ¼ computerized tomography ED ¼ effective dose FBP ¼ filtered back projection FT ¼ fluoroscopy time IVP ¼ excretory urogram KUB ¼ plain x-ray of kidneys, ureters and bladder LDCT ¼ low dose CT NCCT ¼ noncontrast CT PNL ¼ percutaneous nephrolithotomy SWL ¼ shock wave lithotripsy ULDCT ¼ ultra LDCT URS ¼ ureteroscopy US ¼ ultrasound W T ¼ weighting factor Accepted for publication April 2, * Correspondence: Duke University Medical Center, DUMC 3167, Durham, North Carolina (telephone: ; FAX: ; michael.lipkin@duke.edu). Purpose: There is rising concern over the increasing amount of patient radiation exposure from diagnostic imaging and medical procedures. Patients with nephrolithiasis are at potentially significant risk for radiation exposure due to the need for imaging to manage recurrent stone disease. We reviewed the literature in an attempt to better characterize actual risks and discussed methods to reduce radiation exposure for adult patients with nephrolithiasis. Materials and Methods: A PubMedÒ search was performed using the key words nephrolithiasis, stones, radiation, fluoroscopy, ureteroscopy, percutaneous nephrolithotomy, computerized tomography and shock wave lithotripsy. Additional citations were identified by reviewing reference lists of pertinent articles. Results: A total of 50 relevant articles were included in this review. Patients with a first time acute stone event are exposed to a significant amount of radiation. Most radiation is from computerized tomography. Patients undergoing percutaneous nephrolithotomy are exposed to an equal or greater amount of radiation than they received from computerized tomography. Risk factors for increased exposure during percutaneous nephrolithotomy include obesity, multiple tracts and a larger stone burden. Ureteroscopy exposes patients to approximately the same amount of radiation as plain x-ray of the kidneys, ureters and bladder. Risk factors for increased exposure during ureteroscopy include obesity and ureteral dilation. During shock wave lithotripsy the amount of radiation exposure is not well characterized. Interventions to reduce exposure to patients include using ultrasound when possible and implementing low dose computerized tomography protocols. The as low as reasonably achievable principle of radiation exposure should always be followed when fluoroscopy is performed. The use of an air retrograde pyelogram may also reduce exposure during percutaneous nephrolithotomy. Fluoroscopy time during ureteroscopy may be decreased by a laser guided C-arm, a dedicated C-arm technician, stent placement under direct vision and tactile feedback to help guide wire placement. Conclusions: Patients with nephrolithiasis are at significant risk for increased radiation exposure from the imaging and fluoroscopy used during treatment. The true risks of low radiation exposure remain uncertain. It is important to be aware of these risks to provide better counseling for patients. Urologists must also be familiar with techniques to decrease radiation exposure for patients with nephrolithiasis. Key Words: kidney, nephrolithiasis, radiation dosage, fluoroscopy, diagnostic imaging 878 j /15/ /0 THE JOURNAL OF UROLOGY Ó 2015 by AMERICAN UROLOGICAL ASSOCIATION EDUCATION AND RESEARCH,INC. Vol. 194, , October 2015 Printed in U.S.A.

2 RADIATION EXPOSURE DURING EVALUATION AND MANAGEMENT OF NEPHROLITHIASIS 879 THERE is heightened awareness and increased concern over radiation exposure to the adult patient population in recent years. From 1982 to 2006 the per capita radiation exposure from medical sources in the United States increased nearly 600% from 0.54 to 3.0 msv. 1 Increased use of CT is responsible for most of this change. The number of CTs performed in the United States increased from approximately 5 million in 1980 to 62 million in In addition to CT, radiation from nuclear medicine studies, plain radiographs and fluoroscopy all contribute to the increase in medical radiation exposure. 1 When discussing medical radiation exposure, an understanding of basic terminology and concepts is important. Absorbed dose is the amount of energy absorbed per mass of tissue or an organ. 3 The unit is J/kg or Gy. ED is a calculated value that relates the absorbed dose to the deleterious effects of exposure such as the risk of malignancy. The unit for ED is Sv. In the context of medical exposure ED is usually expressed in msv. It is determined by directly measuring at least 20 individual organ absorbed doses. 4 These absorbed doses are multiplied by the appropriate tissue W T of each organ to provide an equivalent dose. W T is determined by the ICRP (International Commission on Radiological Protection). 3 It is weighted based on the relative radiosensitivity of different organs with a higher W T given to more radiosensitive organs. The equivalent doses are summed to provide the ED. The dose area product is expressed in Gy cm 2 and calculated from the radiation dose to air multiplied by the area of the x-ray field. This value correlates well with the total energy imparted to the subject undergoing medical radiation exposure and, therefore, it relates to ED and overall malignancy risk. ED can be estimated by combining dose area product with the appropriate coefficient (varies for the protocol used and irradiated portion of body) derived from the Monte Carlo simulations with anthropomorphic digital phantoms. 4,5 FT is the value that represents the length of time that fluoroscopy is used during an intervention. FT is not a reliable measurement of dose as it does not account for the fluoroscopy dose rate or the dose due to radiography (ie digital subtraction angiography). 6 SSDI (size specific dose estimate) is a novel method of reporting patient radiation dose. The concept accounts for patient size and is derived from multiplying CTDI vol (volume CT dose index), a standardized measure of average scanner output, by a size dependent conversion factor. Increases in patient size decrease size specific dose estimates. 7 There are 2 types of generalizable effects from radiation exposure, including deterministic effects and stochastic effects. Deterministic effects are characterized by having a threshold dose below which there is an absence of tissue reactions. Above the threshold dose there is tissue reaction and injury with increases in severity with increasing dose. An example of a deterministic effect is skin injury from radiation, which can occur above a threshold dose of 2 Gy. Stochastic effects are characterized by the absence of a threshold dose. Increased levels of exposure do not affect the type or severity of the effect but they do increase the probability of an effect. 3 The risk of malignancy from radiation exposure is a stochastic effect. Common malignancies include leukemia, multiple myeloma, and thyroid, bladder, breast, lung, ovarian and colon cancers. Currently the NCRP (National Council on Radiation Protection and Measurements) has recommended an annual occupational limit of 50 msv. 8 In medicine there are no suggested limits for patient exposure. Instead the risks of radiation must be balanced with the clinical necessity and benefit of the imaging study or procedure. Patients with nephrolithiasis are at risk for significant radiation exposure. Diagnostic imaging such as CT, KUB, IVP and nuclear medicine renal scans are all commonly used to evaluate stone patients. Fluoroscopy during PNL, URS and SWL also contributes to the overall radiation to which patients with nephrolithiasis are exposed. CT and KUB for followup of stone patients also contribute to radiation exposure. MATERIALS AND METHODS We performed a comprehensive PubMedÒ search of articles published from January 1, 2004 through December 31, 2014 using the key words nephrolithiasis, stones, radiation, fluoroscopy, ureteroscopy, percutaneous nephrolithotomy, CT imaging and shock wave lithotripsy. Relevant original research articles and reviews published in the English language and with an abstract available for review were considered. We excluded expert opinions, editorials and case reports. Additional citations were identified by reviewing reference lists of pertinent articles. Articles within the scope of this review were selected based on contents. RESULTS We retrieved a total of 835 articles. A total of 50 relevant articles were selected for inclusion in this review. Exposure During Stone Event Patients undergoing evaluation and management for nephrolithiasis are at risk for significant radiation exposure ranging from 1.18 to msv. 9 The use of imaging modalities has significantly increased in recent decades, particularly NCCT.

3 880 RADIATION EXPOSURE DURING EVALUATION AND MANAGEMENT OF NEPHROLITHIASIS This is the most sensitive and specific imaging test for nephrolithiasis and it is considered the first line imaging study to diagnose urolithiasis. A study from 2 academic centers evaluating imaging use during an acute stone episode demonstrated that patients typically undergo 4 radiographic studies in the 1-year period after a stone episode, averaging 1.2 KUBs, 1.7 NCCTs and 1 IVP. 10 Radiation exposure during a single stone episode averages 5.3 msv. Patients who required NCCT during the evaluation received much higher radiation exposure with a median ED of msv. 9 Exposure from Diagnostic Imaging NCCT radiation doses. NCCT studies remain the study of choice to evaluate patients with acute renal colic. With a reported sensitivity and specificity of 95% and 98%, respectively, NCCT accurately evaluates ureterolithiasis in patients with acute flank pain. 11 NCCT is capable of acquiring anatomical details of the urinary system and it defines the density of most stone types (matrix or indinavir-like compositions being the exceptions), which can aid with management and composition determination. This imaging modality can be rapidly performed, does not require contrast medium and importantly can help determine most pathological conditions present outside the urinary tract. 12 A conventional NCCT study of the abdomen and pelvis is 10 to 20 msv. 2 However, the amount of radiation delivered varies with the machine and protocol used. A study using an anthropomorphic male phantom determined that the ED for a stone protocol NCCT was 3.04 msv with a 64-slice volume computed tomography scanner (GE Healthcare, Little Chalfont, United Kingdom). 13,14 Another study looking at 49,903 renal colic protocol CT studies at 93 institutions from May 2011 to January 2013 showed the mean ED to be 11.2 msv. 15 It has been established that there are variations in mean ED despite similar imaging protocols within and across institutions. This finding has been determined to be as much as a 13-fold variation with highest variations observed in abdomen and pelvis CT studies. 16 These variations can be attributed to several components, including differences in patient populations, CT scanner equipment and technique factors such as tube current, peak kilovoltage and pitch. NCCT vs US. US is an alternative imaging modality used to evaluate patients with known or suspected renal and ureteral calculi. US does not emit ionizing radiation and it is noninvasive, making it an ideal first line study for pediatric and pregnant patients. Furthermore, US costs substantially less than CT, on average a fifth of a CT study. 17 A systematic review of the literature revealed a cumulative sensitivity and specificity of 45% and 88%, respectively, to detect renal calculi with US. 18 Diagnosis is improved in patients 35 years or younger and with a BMI of 24 kg/m 2 or less. 19 However, US can also overestimate stone size in urolithiasis. A retrospective study demonstrated that for stones 5 mm or less US measurements were an average of 1.0 mm greater than CT measurements (p <0.001). Measurements by US and CT in this study were discordant for 60% of the stones 5 mm or less. Correlation of findings between US and NCCT seemed to decrease with smaller stone size and ureteral location. 12 These comparative studies did not incorporate US findings such as the twinkling artifact, which is also associated with renal calculi and increases test specificity. 20 A recent multicenter study of initial imaging method for patients with suspected nephrolithiasis demonstrated that initial US was associated with lower cumulative radiation exposure than initial NCCT. There were also no significant differences in complications such as hospitalizations, return emergency department visits or serious adverse events when comparing initial US and initial NCCT for suspected nephrolithiasis. 21 Various studies continue to recommend US as the first choice for diagnostic purposes in consideration of costs, absence of radiation exposure and universal availability. 19 Low dose CT. Recent innovations in CT scanners and protocols have enabled the development of low dose NCCT. Due to increasing concern of radiation exposure, particularly for young patients, LDCT has increased in use and reduced radiation. A number of groups have investigated the efficacy of LDCT for evaluating stone patients. A metaanalysis of LDCT studies from 1995 to 2007 revealed a pooled sensitivity and specificity of 96.6% and 94.9%, respectively, to diagnose urolithiasis. 22 This finding is comparable to that of NCCT and delivers a mean ED of 1.40 msv in males and 1.97 msv in females. Stone attenuation from CT studies can be used to differentiate various stone compositions. Automatic tube current modulation, pitch augmentation, tube voltage reduction and scan range control are various methods used to achieve LDCT scans. However, these approaches are limited in radiation dose reduction due to the inherent constraints of the conventional FBP reconstruction algorithm. Scans with the FBP algorithm at reduced doses produce image noise, therefore compromising diagnostic quality. 23 Recent innovations have enabled the development of advanced ultralow dose iterative reconstruction algorithms, which preserve image quality at low doses, making it now possible to evaluate urolithiasis with ULDCT.

4 RADIATION EXPOSURE DURING EVALUATION AND MANAGEMENT OF NEPHROLITHIASIS 881 Compared to LDCT, ULDCT is a protocol that delivers an ED of less than 1 msv. The first generation of iterative reconstruction algorithms such as ASIR (adaptive statistical iterative reconstruction) decreases noise on reconstructed CT images and reduces radiation doses by 23% to 66% compared to LDCT. 24 More recent complex iterative reconstruction algorithms such as MBIR (model based iterative reconstruction) account for photon statistics, electronic noise, size of focal spots and detectors, leading to further dose reduction (70% to 90%) while maintaining images of diagnostic quality. 25 A prospective trial comparing ULDCT and LDCT demonstrated that ULDCT remained accurate for stone detection at EDs less than 2-view KUBs. For renal calculi at a 4 mm threshold the sensitivity of ULDCT is approximately 91%. 26 Recently CT doses equivalent to those of a 1-view KUB were evaluated to detect calculi. In a CT study with an ED of 0.5 msv in males and 0.7 msv in females the sensitivity and specificity for detecting calculi was 97% and 95%, respectively. 27 In another prospective study CT with a mean ED of 0.48 msv detected calculi greater than 3 mm with a sensitivity and specificity of 87% and 100%, respectively. 28 However, pooled sensitivity and specificity was 72% and 94%, respectively, due to the poor detection of calculi less than 3 mm. While these technological innovations are now being integrated into routine clinical practice, the impact of novel CT protocols on outcomes such as severe adverse events and return emergency room visits has not been investigated. These studies demonstrate that LDCT is an effective alternative in the diagnosis of ureteral calculi but there are limitations. In particular it has been demonstrated that sensitivity and specificity for detecting ureteral calculi with LDCT is decreased in overweight patients when using extremely low radiation doses (less than 1 msv). When BMI is considered, LDCT with 1.6 to 2.1 msv is able to detect stones with 96% sensitivity and 100% specificity in patients with a BMI less than 30 kg/m In patients with a BMI greater than 30 kg/m 2 sensitivity and specificity decrease to 50% and 89%, respectively, at this dose. The threshold where the sensitivity and specificity of LDCT is compromised due to too low a BMI remains poorly defined. LDCT as an imaging modality is also limited in detecting clinically significant extraurinary tract findings, possibly leading to missed findings during patient evaluations, including distal ureteral obstruction, acute appendicitis and ovarian dermoid. 28 While LDCT becomes a less effective tool when evaluating patients with stones less than 2 to 3 mm, stones less than 5 mm rarely require urological intervention due to the likelihood of spontaneous passage. 29 The advancement of medical imaging has introduced novel methods to overcome issues with poor image quality when using LDCT, particularly in obese patients. ATM (automatic tube current modulation) adjusts gantry rotation time to optimize the signal-to-noise ratio. However, LDCT with ATM delivers as much as a threefold increase in radiation dose to obese patients. 30 Iterative reconstruction algorithms and noise reduction methods are currently being investigated as approaches to optimize CT protocols for obese patients. A recent phantom study with FBP reported a 15% to 37% image noise reduction but no improvements in low contrast detectability. 31 In an alternate study radiation doses to obese patients were reduced 31.5% with the ASIR algorithm. 32 While image quality was preserved, the study did not formally assess diagnostic effectiveness. The AUA (American Urological Association) currently recommends standard NCCT over LDCT to evaluate stones in obese patients because sensitivity for detection is decreased in patients with a BMI of greater than 30 kg/m KUB/IVP radiation doses. Although NCCT is considered the gold standard for evaluating patients with acute colic, the use of KUB persists in the clinical setting. KUB can track the passage of radiopaque stones in patients who are being treated conservatively or those on medical expulsive therapy. The radiation dose of KUB varies with patient size, settings and machinery but it has been reported to be an ED of approximately 0.63 to 1.1 msv per film. 13 However, the use of tomograms with KUB increases radiation doses. Sensitivity is increased for detection when both modalities are used but the ED of a KUB with 3 tomograms is 3.93 msv. 13 Before the introduction of NCCT to evaluate acute ureterolithiasis IVP was used for years to determine ureteral obstruction. IVP is an invasive procedure that may cause delays in diagnosis and treatment when obstruction is present and it has an associated risk of contrast material reaction. When obstruction is absent, IVP often fails to identify other causes of acute flank pain. The radiation dose from an IVP varies depending on the technique and number of images taken. The ED of IVP has been reported in the literature to be approximately 3.0 msv. 14 Digital tomosynthesis. Digital tomosynthesis is a novel technology based on a series of low dose images acquired by a digital detector during a single tomographic sweep. A scout plain KUB is first acquired and then a single tomographic sweep is obtained. Digital software reconstructs the data from the tomographic sweep to produce a series of coronal images at specified slice intervals, and at a start and end height. Overlying structures are removed to help produce clear images and provide

5 882 RADIATION EXPOSURE DURING EVALUATION AND MANAGEMENT OF NEPHROLITHIASIS depth information about structures of interest. However, only slices parallel to the detector plane can be obtained. There is also a loss of overview due to blurring outside the determined region of interest. To date the evaluation of digital tomosynthesis in a clinical setting for patients with suspected ureterolithiasis has been limited. This technology has been primarily used in chest radiography and breast imaging. The literature reports an ED of 0.83 to 0.85 msv, which is significantly less than the ED of standard NCCT and KUB with tomograms but more than the ED of a plain KUB. 34 Radiation reduction. Patients undergoing treatment for nephrolithiasis are at risk for significant radiation exposure partly due to the increasing use of diagnostic and followup imaging. Radiation exposure can be reduced by proper selection of imaging studies and application of radiation-free imaging such as US. Additionally, the use of LDCT and ULDCT over NCCT offers the advantage of less radiation exposure while also maintaining similar sensitivity and specificity to detect calculi in select patients, particularly in nonobese patients. Recently the AUA offered recommendations for imaging ureteral calculi, taking into account sensitivity and specificity of the imaging modalities, cost and radiation exposure. 33 For initial presentation the recommendation is LDCT for patients with a BMI of less than 30 kg/m 2 and a standard NCCT for those with a BMI of 30 kg/m 2 or greater. For the followup of patients on medical expulsive therapy those who have a stone visible on KUB should undergo repeat KUB and US. After the surgical management of ureteral stones with either URS or SWL the recommendation is for followup imaging with either US alone or in conjunction with KUB. However, recent large multicenter trials have suggested that an update of current guidelines on initial imaging modality for suspected nephrolithiasis is necessary. Initial US instead of CT lowers radiation exposure without leading to significant differences in complications such as hospitalizations or return emergency room visits. 19,21 While guidelines can impact clinical decision making, they alone will likely not reduce CT use. Current guidelines recommend initial US for children with suspected nephrolithiasis and yet only 24% of children underwent US as the initial study from 2003 to Exposure from Interventions Percutaneous nephrolithotomy. Fluoroscopy is typically performed during PNL to guide percutaneous access and evaluate for residual stone. However, fluoroscopy use in the clinical setting signifies exposure to ionizing radiation. There have been various investigations evaluating the typical radiation exposure from fluoroscopy during PNL. A retrospective review of 96 patients determined the mean ED for patients undergoing PNL to be 8.66 msv. 36 In a different study using a validated anthropomorphic adult male phantom the findings were similar. 37 The ED for a right PNL was 7.63 msv and the ED for a left PNL 8.11 msv. However, the group also quantified the specific absorbed radiation dose for each organ location during 10-minute fluoroscopy trials and found that the skin entrance during left and right PNL was exposed to the greatest amount of radiation, that is 0.24 and 0.26 mgy per second, respectively. There are certain risk factors that increase radiation exposure during PNL, including high BMI, increased stone burden and an increased number of access tracts. 36,38,39 In a retrospective study of the factors affecting FT during PNL patients with large stones and a requirement for multiple access tracts underwent significantly prolonged FT. 38 In a prospective study of PNL and obesity, total operative time and radiation exposure increased as patient BMI increased, in part due to technical challenges. 39 Obesity increased FT by 36% and mean ED by 177%. A separate retrospective review had similar findings. 36 Obese patients with a BMI of 30 to 39.9 kg/m 2 had more than a twofold increase in mean ED compared to patients with a BMI of less than 25 kg/ m 2 (6.49 vs 2.66 msv). Morbidly obese patients with a BMI of 40 kg/m 2 or greater had more than a threefold increase in mean ED compared to patients with a BMI of less than 25 kg/m 2 (9.13 vs 2.66 msv). Methods to reduce exposure. Various techniques can decrease radiation exposure. Room air for retrograde identification of calyceal anatomy has been successfully used. While the use of room air is not associated with decreased FT, the substitution for iodinated contrast medium significantly decreases ED to patients. This has been demonstrated to be as much as a 50% reduction from 7.67 to 4.45 msv. 40 It is due to the automated tube brightness control on most modern C-arms, which lower tube voltage when air is in the field since it is less dense, thereby decreasing the radiation dose compared to contrast material. FT can be limited by applying US to guide access in patients with a BMI of less than 30 kg/m 2. Two randomized, controlled trials compared PNL with ultrasound and fluoroscopy vs fluoroscopy alone. US significantly reduced FT from 28.6 to 14.4 seconds (p <0.01) and from 0.95 to 0.69 minutes (p ¼ ). 41,42 There have been reports of PNL performed without fluoroscopy and relying solely on US as guidance, therefore, eliminating radiation exposure to both patient and urologist. The outcomes of PNL with US in patients with stones 2 to 4 cm and a BMI of less than 30 kg/m 2 were similar to the

6 RADIATION EXPOSURE DURING EVALUATION AND MANAGEMENT OF NEPHROLITHIASIS 883 outcomes of PNL in patients with fluoroscopic guidance. 43 A 5-year study of more than 700 PNL cases guided only by US suggests that total US guided PNL is a safe and convenient procedure without any major complications. 44 However, successful US in obese patients is limited due to difficulty in imaging the kidneys. 43 The ALARA principle of radiation exposure should be followed during procedures that require fluoroscopy. Pulsed fluoroscopy should be set at the lowest possible frames per second that provide an image quality adequate to perform PNL. Additionally, the image intensifier should be as close to the patient as possible and the image should be collimated as much as possible over the area of interest. A drape placed over or under the patient helps reduce scatter radiation. Last image hold should be used to capture and transfer images that can be used as a reference during PNL. 6 URS exposure and doses. Radiation during URS contributes to the radiation received by patients with ureteral stones. A validated anthropomorphic model with a nonobese male demonstrated the ED rate for URS to be msv per second. 45 In this study the investigators reviewed their series of URS and found a median FT of seconds and a median ED of 1.13 msv. While radiation exposure during URS is significantly less than during PNL, similar risk factors exist for increased radiation exposure in URS. In clinical practice patients with severe obesity have been demonstrated to have a threefold higher radiation dose rate during URS. 46 The automatic exposure control in modern C-arms adjusts tube voltage and tube current to appropriately preserve image quality. The end effect is to expose obese patients to significantly more radiation. Methods to reduce exposure during URS. The principle of ALARA should be applied to fluoroscopy use during URS. The implementation of a reduced radiation fluoroscopy protocol during URS can decrease FT as well. Incorporating several measures, such as using a laser guided C-arm, last image hold, a preoperative fluoroscopy checklist and tactile clues for guide wire placement, has been demonstrated to reduce FT by as much as 82% from 86.1 to 15.5 seconds without altering patient outcomes. 6,47 There have even been successful reports of protocols with no fluoroscopy use during URS, relying solely on measures such as tactile and visual feedback. 48 Providing urologists with simple feedback on FT in operations has been demonstrated to decrease FT for URS by as much as 24% from 2.74 to 2.08 minutes. 49 The promotion of physician awareness through a simple tracking and feedback system requires minimal change to existing process flows in the operating room. Shock wave lithotripsy. SWL uses fluoroscopy to target a stone for treatment. Radiation exposure varies by gender and anatomical location of the stone. A study using an anthropomorphic phantom and TLD determined that the mean total ED in male and female patients was 1.71 msv and 1.82 msv, respectively. 50 However, for distal ureteral stones the mean total ED for male and female patients was 0.76 and 1.62 msv, respectively. Mean total ED is higher for female patients and for proximal ureteral stones. CONCLUSIONS AND RECOMMENDATIONS Patients with urolithiasis are at significant risk for radiation exposure from diagnostic imaging and interventional procedures during medical management. Dosages from imaging can vary and constantly change. Although there is no optimal dose, it is important to follow the principles of ALARA. The risks of low radiation exposure remain uncertain and the long-term implications of repeated low doses of radiation need to be further explored. Improvements in radiation-free techniques for imaging stones would also be useful. Regardless it is important for urologists to be aware of these hazards to provide better counseling to patients and facilitate discussion of risks and benefits. Urologists also must be familiar with techniques to reduce radiation exposure for their patients with nephrolithiasis. We recommend using LDCT and US when possible. The principle of ALARA should always be followed when performing fluoroscopy during procedural interventions. Reduced fluoroscopy protocols may decrease radiation exposure during interventions as well. REFERENCES 1. Mettler FA Jr, Thomadsen BR, Bhargavan M et al: Medical radiation exposure in the U.S. in 2006: preliminary results. Health Phys 2008; 95: Brenner DJ and Hall EJ: Computed tomographydan increasing source of radiation exposure. N Engl J Med 2007; 357: The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. 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