Indian Journal of Urology
SYMPOSIUM
Year
: 2014  |  Volume : 30  |  Issue : 1  |  Page : 55--59

As low as reasonably achievable: Methods for reducing radiation exposure during the management of renal and ureteral stones


Fernando Cabrera, Glenn M Preminger, Michael E Lipkin 
 Duke Comprehensive Kidney Stone Center, Department of Urology, Duke University Medical Center, Durham, North Carolina, USA

Correspondence Address:
Glenn M Preminger
Duke University Medical Center, Department of Urology, DUMC 3167, Dirham, North Carolina 27710
USA

Abstract

Imaging for urolithiasis has evolved over the past 30 years. Currently, non-contrast computed tomography (NCCT) remains the first line imaging modality for the evaluation of patients with suspected urolithiasis. NCCT is a dominant source of ionizing radiation for patients and one of its major limitation. However, new low dose NCCT protocols may help to reduce the risk. Fluoroscopy use during operating room (OR) surgical procedures can be a substantial source of radiation for patients, OR staff and surgeons. It is important to consider the amount of radiation patients are exposed to from fluoroscopy during operative interventions for stones. Radiation reduction can be accomplished by appropriate selection of imaging studies and multiple techniques, which minimize the use of fluoroscopy whenever possible. The purpose of this manuscript is to review common imaging modalities used for diagnosing and management of renal and ureteral stones associated with radiation exposure. We also review alternatives and techniques to reduce radiation exposure.



How to cite this article:
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;30:55-59


How to cite this URL:
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 [serial online] 2014 [cited 2019 Aug 21 ];30:55-59
Available from: http://www.indianjurol.com/text.asp?2014/30/1/55/124208


Full Text

 Introduction



Imaging is a key component in the evaluation and management of patients with urolithiasis. Beyond diagnosis, imaging provides important information that allows urologists to determine the most appropriate treatment modality for the patient. This information includes the size, location and in some cases the stone composition. [1],[2]

Plain abdominal radiography kidneys, ureters and bladder (KUB) and excretory radiography intravenous pyelogram have been largely supplanted by non-contrast computed tomography (NCCT) of the abdomen and pelvis (NCCT) for the initial diagnosis and follow-up of urolithiasis. [3],[4],[5] Ultrasound has also been used in place of traditional radiography. [6],[7],[8]

Patients with urolithiasis are at risk for recurrence and therefore are exposed to significant radiation exposure from imaging studies. Recent studies show growing concern over radiation exposure from imaging studies. NCCT is a dominant source of radiation in these patients. Plain radiography (KUB) and digital tomosynthesis (DT) are other modalities used in the evaluation and follow-up of nephrolithiasis, but incur in less radiation exposure. [9] The effective doses (EDs) for a stone protocol NCCT was 3.04 ± 0.34 mSv. The ED for a KUB was 0.63 and 1.1 mSv for the additional tomographic film. The total ED for intravenous urogram was 3.93 mSv. The ED for DT performed with two scouts and one sweep (14.2°) was 0.83 mSv. [9] [Table 1] summarizes ED associated with common imaging modalities used in the follow-up of patients with urolithiasis. [9] Once diagnosed with a stone, a significant number of patients will undergo surgical intervention. Fluoroscopy used during shock wave lithotripsy (SWL), ureteroscopy (URS) and percutaneous nephrolithotomy (PNL) contributes to the overall radiation exposure of patients with urolithiasis. [10],[11],[12]{Table 1}

This article will describe methods to reduce radiation exposure from commonly performed imaging studies for the diagnosis and management of urolithiasis.

 Evaluation of Renal Colic



NCCT is currently considered the first line imaging study for the evaluation of the patient with acute flank pain and a suspected stone. NCCT has a reported sensitivity of 95-98% and specificity of 96-98% for the diagnosis of a ureteral stone in a patient with acute flank pain. [4] Beyond identifying the stone, NCCT allows for evaluation of signs of obstruction associated with ureteral stones. In patients with ureteral stones, NCCT was able to identify hydroureter in 82.7%, hydronephrosis in 80%, peri-ureteric edema in 59% and unilateral renal enlargement in 57.2% respectively. [13],[14]

When evaluating patients with acute flank pain, NCCT also has the ability to assess the rest of the abdominal and pelvic organs and possibly identify other causes for pain. In a series of 1000 consecutive NCCT performed for the evaluation of renal colic, an alternative diagnosis for their presenting symptoms was made in 10.1% of the cases. [15]

 Pre-Operative Evaluation



Beyond the diagnosis stones, NCCT is useful in the pre-operative planning for the treatment of stones. Stone size and location are easily evaluated with NCCT. When planning SWL, the skin to stone distance can be determined on pre-operative NCCT. Prone NCCT can also be useful for the pre-operative evaluation for planning prone PNL. Prone NCCT can determine the anatomic relations of adjacent organs and the pleura with upper pole calyces. This information can help determine the feasibility and risk of complication of an upper pole puncture during prone PNL.

 Radiation Reduction



Radiation exposure from medical sources has been steadily increasing over the past three decades. [16],[17] There have been approximately more than 62 million computed tomography (CTs) performed in the US by the year 2006. [18] The approximate organ dose from a typical NCCT is similar to the radiation exposure of the atomic bomb survivors. [18] It is estimated that an additional 29,000 cancers could be related to CT scans performed in the US in 2007. [19] Some of the studies show that cancer rates can be doubled in younger patients. [20] Patients with urolithiasis are at increased risk for significant radiation exposure from diagnostic imaging, specifically NCCT. From 1996 to 2007, the use of NCCT to assess patients with suspected stones increased significantly from 4% to 42.5%. [13] The use of NCCT for evaluation of flank pain in the emergency room has increased significantly from 19.6% to 45.5% of patient visits over the past decade. It has been reported that patients undergo a median of 1.7 NCCT in a 1 year period following an acute stone episode. [21]

Fluoroscopy utilized during surgical interventions also contributes to these patients' overall radiation exposure. Given that patients with urolithiasis constitute a high risk population, measures to reduce the amount of radiation these patients are exposed to are extremely important.

 Selection of Appropriate Imaging Studies



Proper selection of imaging studies for the evaluation of urolithiasis is an important way to reduce radiation. Whenever possible, radiation free techniques such as ultrasound or magnetic resonance imaging (MRI) should be used. Ultrasound should be considered the first line imaging study for the evaluation of stones or renal colic in pediatric patients and pregnant women. The use of MRI has also been reported for evaluation of renal colic in pregnant women. [22]

The combination of ultrasound and KUB has been shown to have high sensitivity for the diagnosis of ureteral stones and exposes patients to less radiation than a NCCT.

The American Urological Association recently submitted guidelines regarding appropriate imaging selection for the evaluation of ureteral calculi. [23] The authors recommend "low dose" NCCT as the initial imaging modality for a patient with flank pain and a suspected ureteral stone if the body mass index is less than 30 kg/m 2 and a standard dose NCCT if the patient is obese. They recommend a KUB concurrently with the NCCT if the stone is not seen on the scout image. For follow up of radio-opaque stones, they recommend ultrasound along with KUB. In cases of radio-lucent stones, they recommend follow-up imaging with NCCT.

 Low-Dose CT



Though ultrasound and MRI can be used for the evaluation of patients with urolithiasis, NCCT has the highest sensitivity and specificity for the diagnosis of stones. NCCT is also very valuable for pre-operative planning. The amount of radiation a patient is exposed to from a NCCT of the abdomen and pelvis is dependent on the protocol and machine used, as well as patient characteristics. For a standard NCCT of the abdomen and pelvis performed for the evaluation of stones, the ED has been reported to be as high as 9.6 mSv for men and 12.6 mSv for women.

With the advent of new CT scanner technology and new software, NCCT for the evaluation of urolithiasis can be performed with lower radiation doses while maintaining diagnostic accuracy. These "low-dose" CT scans can greatly reduce the amount of radiation patients with urolithiasis are exposed to. There is no standard definition for "low-dose" CT. A recent meta-analysis evaluating the performance of low dose CT for the diagnosis of urolithiasis defined low-dose CT as applying an ED <3 mSv for the entire examination. [24]

There have been a number of reports assessing the effectiveness of low-dose CT for the evaluation of stones and renal colic. [25] One report compared a standard NCCT at a dose of 7.3-10 mSv versus a low dose NCCT at 1.4-1.97 mSv for the evaluation of acute renal colic. Low dose NCCT had equivalent sensitivities to standard NCCT for the diagnosis of ureteral stones with the exception of ureteral stones <2 mm. In these cases, the sensitivity of low dose NCCT was 68-79% versus 95% sensitivity for the standard dose NCCT. [25]

Low-dose NCCT has been shown to be useful for the follow-up of recurrent stone formers to evaluate for new stone formation or stone growth. In a recent study of 62 patients that underwent NCCT for the detection of urolithiasis. Images were modified by adding image noise to simulate reduced tube current level. Even at a dose reduction of 56%, the authors reported no significant intra-observer or inter-observer differences for the detection of urolithiasis. [26] Low-dose CT has also been reported for the evaluation of renal colic and flank pain in pregnant patients with high sensitivity and specificity. [27]

Low dose NCCT appears to perform as well as standard NCCT for the evaluation of urolithiasis and in cases where NCCT is to be performed, low dose NCCT should be considered the first line imaging study.

 Fluoroscoy



Fluoroscopy is commonly used during surgical procedures to treat patients with urolithiasis including SWL, URS and PNL. Therefore, patients who undergo treatment for stones are exposed to even more radiation. The amount of radiation patients are exposed to during PNL and URS has been quantified using a validated model. Organ specific radiation doses have been calculated and found greatest at the skin entrance, where exposure during left and right PNL, was 0.24 mGy/s and 0.26 mGy/s, respectively. [28] Median fluoroscopic procedure exposures were 43.3 mGy for patients who were undergoing PNL and 27.6 mGy for those patients undergoing URS. [29] There are a number of methods to reduce the amount of radiation patients are exposed to in the operating room (OR). [30],[31],[32],[33]

 As Low as Reasonably Achievable



The principle of ALARA should always be applied when using fluoroscopy. The practice of minimizing the exposed area and image during fluoroscopy is called collimation. Collimating the image and placing the image intensifier as close to the patient as possible has been shown to decrease during surgical procedures. [34],[35] Other techniques include pulsed fluoroscopy, which should be used at the lowest possible frames/s that provides usable image quality to perform the procedure. "Last image hold" should be utilized to save and transfer images to an adjacent screen to be used as a reference during the procedure. Close adherence to the principles of ALARA has been demonstrated to reduce radiation dose during the pediatric interventional radiology procedures. [36]

 Radiation Reduction During PNL



When performing a retrograde pyelogram to aide in fluoroscopic access during PNL, the use of air instead of iodinated contrast may reduce radiation exposure. A retrospective review of 96 PNL procedures demonstrated that the use of air reduced radiation exposure nearly 50% when compared with contrast, 4.45 mSv versus 7.67 mSv (P = 0.001). [30]

The use of ultrasound to obtain access also can reduce radiation exposure by reducing or eliminating the need for fluoroscopy. There have been a number of reports on the use of ultrasound to aide in access during PNL. Two randomized controlled trials have been performed comparing PNL with ultrasound combined with fluoroscopy versus fluoroscopy alone. [7],[37] Though these trials demonstrated a reduction in fluoroscopy time with ultrasound, the patients were still exposed to a small amount of radiation from fluoroscopy. The ideal situation to reduce radiation exposure would be to eliminate fluoroscopy altogether. Studies have demonstrated the feasibility and safety of performing PNL with ultrasound alone in a select patient population.

 Radiation Reduction During URS



The same principles of ALARA apply to fluoroscopy use during URS. In addition, there have been reports on methods to reduce fluoroscopy time for URS. One group of investigators demonstrated a 24% reduction in fluoroscopy time when surgeons were given periodic reports documenting their mean fluoroscopy time compared with that of their peers. [38] In addition, intra-operative techniques have been reported to reduce fluoroscopy time during URS. These measures include the use of a laser guided C-arm, tactile cues for the placement of guidewires, stent placement under direct vision through a cystoscope, use of a designated fluoroscopy technician, and single pulse fluoroscopy mode for portions of the case. When these measures were implemented, the authors reported a reduction in the mean fluoroscopy time during URS from 86.1 s to 15.5 s. This fluoroscopy protocol resulted in an 82% reduction in fluoroscopy time without altering patient outcomes. [39]

 Radiation Reduction During SWL



The principles of ALARA apply to the use of fluoroscopy during SWL as well. In addition, ultrasound can be used to target the stone instead of fluoroscopy with good success.

 Summary



Imaging plays an important role in the evaluation of patients with urolithiasis. NCCT of the abdomen and pelvis is the most sensitive and specific imaging modality for diagnosing stones. Images from NCCT also play an important role in determining the best surgical approach to treat a stone. When NCCT is performed for the evaluation of stones, a "low dose" protocol should be used to reduce the amount of radiation these patients are exposed to. Ultrasound is also useful in the evaluation of urolithiasis. Ultrasound should be considered first line imaging for stones in pediatric and pregnant patients. Ultrasound has decreased sensitivity and specificity for identifying stones compared with NCCT, however it has nearly equivalent sensitivities and specificities for diagnosing obstruction. Plain abdominal radiography is mostly useful for pre-operative planning prior to SWL and as an adjunct to ultrasound. The role of MRI in the evaluation of urolithiasis is limited.

Stone patients are exposed to significant amounts of radiation from diagnostic imaging, primarily NCCT and fluoroscopy in the OR. Proper imaging modality selection helps to minimize radiation exposure. Following the principles of ALARA in the operating room can help reduce the amount of radiation patients are exposed to from fluoroscopy.

References

1Mostafavi MR, Ernst RD, Saltzman B. Accurate determination of chemical composition of urinary calculi by spiral computerized tomography. J Urol 1998;159:673-5.
2Nakada SY, Hoff DG, Attai S, Heisey D, Blankenbaker D, Pozniak M. Determination of stone composition by noncontrast spiral computed tomography in the clinical setting. Urology 2000;55:816-9.
3Federle MP, McAninch JW, Kaiser JA, Goodman PC, Roberts J, Mall JC. Computed tomography of urinary calculi. AJR Am J Roentgenol 1981;136:255-8.
4Smith RC, Rosenfield AT, Choe KA, Essenmacher KR, Verga M, Glickman MG, et al. Acute flank pain: Comparison of non-contrast-enhanced CT and intravenous urography. Radiology 1995;194:789-94.
5Fielding JR, Steele G, Fox LA, Heller H, Loughlin KR. Spiral computerized tomography in the evaluation of acute flank pain: A replacement for excretory urography. J Urol 1997;157:2071-3.
6Patlas M, Farkas A, Fisher D, Zaghal I, Hadas-Halpern I. Ultrasound vs CT for the detection of ureteric stones in patients with renal colic. Br J Radiol 2001;74:901-4.
7Basiri A, Ziaee AM, Kianian HR, Mehrabi S, Karami H, Moghaddam SM. Ultrasonographic versus fluoroscopic access for percutaneous nephrolithotomy: A randomized clinical trial. J Endourol 2008;22:281-4.
8Passerotti C, Chow JS, Silva A, Schoettler CL, Rosoklija I, Perez-Rossello J, et al. Ultrasound versus computerized tomography for evaluating urolithiasis. J Urol 2009;182:1829-34.
9Astroza GM, Neisius A, Wang AJ, Nguyen G, Toncheva G, Wang C, 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;27:1187-91.
10Balter S, Hopewell JW, Miller DL, Wagner LK, Zelefsky MJ. Fluoroscopically guided interventional procedures: A review of radiation effects on patients' skin and hair. Radiology 2010;254:326-41.
11Majidpour HS. Risk of radiation exposure during PCNL. Urol J 2010;7:87-9.
12Sandilos P, Tsalafoutas I, Koutsokalis G, Karaiskos P, Georgiou E, Yakoumakis E, et al. Radiation doses to patients from extracorporeal shock wave lithotripsy. Health Phys 2006;90:583-7.
13Westphalen AC, Hsia RY, Maselli JH, Wang R, Gonzales R. Radiological imaging of patients with suspected urinary tract stones: National trends, diagnoses, and predictors. Acad Emerg Med 2011;18:699-707.
14Vieweg J, Teh C, Freed K, Leder RA, Smith RH, Nelson RH, et al. Unenhanced helical computerized tomography for the evaluation of patients with acute flank pain. J Urol 1998;160:679-84.
15Hoppe H, Studer R, Kessler TM, Vock P, Studer UE, Thoeny HC. Alternate or additional findings to stone disease on unenhanced computerized tomography for acute flank pain can impact management. J Urol 2006;175:1725-30.
16Mettler FA Jr, Huda W, Yoshizumi TT, Mahesh M. Effective doses in radiology and diagnostic nuclear medicine: A catalog. Radiology 2008;248:254-63.
17Mettler FA Jr, Thomadsen BR, Bhargavan M, Gilley DB, Gray JE, Lipoti JA, et al. Medical radiation exposure in the U.S. in 2006: Preliminary results. Health Phys 2008;95:502-7.
18Brenner DJ, Hall EJ. Computed tomography: An increasing source of radiation exposure. N Engl J Med 2007;357:2277-84.
19Berrington de González A, Mahesh M, Kim KP, Bhargavan M, Lewis R, Mettler F, et al. Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch Intern Med 2009;169:2071-7.
20Smith-Bindman R, Lipson J, Marcus R, Kim KP, Mahesh M, Gould R, et al. Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer. Arch Intern Med 2009;169:2078-86.
21Ferrandino MN, Bagrodia A, Pierre SA, Scales CD Jr, Rampersaud E, Pearle MS, et al. Radiation exposure in the acute and short-term management of urolithiasis at 2 academic centers. J Urol 2009;181:668-72.
22Mullins JK, Semins MJ, Hyams ES, Bohlman ME, Matlaga BR. Half Fourier single-shot turbo spin-echo magnetic resonance urography for the evaluation of suspected renal colic in pregnancy. Urology 2012;79:1252-5.
23Fulgham PF, Assimos DG, Pearle MS, Preminger GM. Clinical effectiveness protocols for imaging in the management of ureteral calculous disease: AUA technology assessment. J Urol 2013;189:1203-13.
24Niemann T, Kollmann T, Bongartz G. Diagnostic performance of low-dose CT for the detection of urolithiasis: A meta-analysis. AJR Am J Roentgenol 2008;191:396-401.
25Kim BS, Hwang IK, Choi YW, Namkung S, Kim HC, Hwang WC, 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.
26Zilberman DE, Tsivian M, Lipkin ME, Ferrandino MN, Frush DP, Paulson EK, et al. Low dose computerized tomography for detection of urolithiasis: Its effectiveness in the setting of the urology clinic. J Urol 2011;185:910-4.
27White WM, Zite NB, Gash J, Waters WB, Thompson W, Klein FA. Low-dose computed tomography for the evaluation of flank pain in the pregnant population. J Endourol 2007;21:1255-60.
28Lipkin ME, Mancini JG, Toncheva G, Wang AJ, Anderson-Evans C, Simmons WN, et al. Organ-specific radiation dose rates and effective dose rates during percutaneous nephrolithotomy. J Endourol 2012;26:439-43.
29Jamal JE, Armenakas NA, Sosa RE, Fracchia JA. Perioperative patient radiation exposure in the endoscopic removal of upper urinary tract calculi. J Endourol 2011;25:1747-51.
30Lipkin ME, Mancini JG, Zilberman DE, Raymundo ME, Yong D, Ferrandino MN, et al. Reduced radiation exposure with the use of an air retrograde pyelogram during fluoroscopic access for percutaneous nephrolithotomy. J Endourol 2011;25:563-7.
31Mues E, Gutiérrez J, Loske AM. Percutaneous renal access: A simplified approach. J Endourol 2007;21:1271-5.
32Kumari G, Kumar P, Wadhwa P, Aron M, Gupta NP, Dogra PN. Radiation exposure to the patient and operating room personnel during percutaneous nephrolithotomy. Int Urol Nephrol 2006;38:207-10.
33Bagley DH, Cubler-Goodman A. Radiation exposure during ureteroscopy. J Urol 1990;144:1356-8.
34Walters TE, Kistler PM, Morton JB, Sparks PB, Halloran K, Kalman JM. Impact of collimation on radiation exposure during interventional electrophysiology. Europace 2012;14:1670-3.
35Mancini JG, Raymundo EM, Lipkin M, Zilberman D, Yong D, Bañez LL, et al. Factors affecting patient radiation exposure during percutaneous nephrolithotomy. J Urol 2010;184:2373-7.
36Sheyn DD, Racadio JM, Ying J, Patel MN, Racadio JM, Johnson ND. Efficacy of a radiation safety education initiative in reducing radiation exposure in the pediatric IR suite. Pediatr Radiol 2008;38:669-74.
37Tzeng BC, Wang CJ, Huang SW, Chang CH. Doppler ultrasound-guided percutaneous nephrolithotomy: A prospective randomized study. Urology 2011;78:535-9.
38Ngo TC, Macleod LC, Rosenstein DI, Reese JH, Shinghal R. Tracking intraoperative fluoroscopy utilization reduces radiation exposure during ureteroscopy. J Endourol 2011;25:763-7.
39Greene DJ, Tenggadjaja CF, Bowman RJ, Agarwal G, Ebrahimi KY, Baldwin DD. Comparison of a reduced radiation fluoroscopy protocol to conventional fluoroscopy during uncomplicated ureteroscopy. Urology 2011;78:286-90.