Effect Of Low Dose Radiation Computerized Tomography Protocols On Distal Ureteral Calculus Detection

Main Category: Urology / Nephrology
Also Included In: Cancer / Oncology;  Radiology / Nuclear Medicine
Article Date: 30 Jan 2010 - 0:00 PDT

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UroToday.com - Stone cancer! While chronic inflammation due to a renal pelvis stone may on very rare occasion be associated with the development of a squamous cell cancer of the collecting system, what is far more common and more worrisome is that our method of diagnosing a ureteral calculus could lead to the later development of a malignancy in 0.1% for each conventional noncontrast CT scan done; overall, CT scanning may be the underlying cause of up to 1.5-2% of all cancers.1,2

While the average KUB exposure is up to 1.0 mSV, a standard 140 mA abdominal/pelvic CT scan creates up to 20mSV of exposure. It is sobering when one realizes that up to 20% of patients, during an acute stone episode may receive multiple CT scans thereby exceeding the 50 mSV annual limit of exposure as recommended by the Food and Drug Administration.3

It is against this backdrop that the authors sought to determine how much the mA seconds could be lowered before the CT scan would fail to detect a urinary tract calculus. This is truly a very innovative and comprehensive study. Using a 26 kg/m2 cadaver, the authors placed 3, 5, and 7 mm stones in the ureters of 7 harvested complete human kidneys, ureters, bladder specimens; anywhere from 0 to 3 stones were placed in each ureter which was then filled with a water-based gel and sutured closed. CT scans were done at 140, 100, 60, 30, 15, and 7.5 mA seconds. The scans were independently reviewed by two study-blinded radiologists. The overall specificity was 98% with a sensitivity of 83% thereby once again justifying the "gold standard" designation of CT scanning for diagnosing renal/ureteral calculi; renal ultrasound has a sensitivity of <77% and KUB has a sensitivity of < 60%.

The sensitivity and specificity at 140 mA seconds was nearly identical to the findings at 7.5mA seconds: 98% vs. 97% and 83% vs. 84%, respectively. At 7.5mA, the reduction in mSV is nearly 95% providing an exposure of only 1mSV, similar to a KUB. These findings have also been documented in two clinical series. 4,5

Now that the word is out, it is up to us as urologists to specifically request these safer low dose protocols of our radiological colleagues. It is frighteningly paradoxical that the means we use to diagnose a benign condition could in turn create a potentially mortal malignant disease process.

Jellison FC, Smith JC, Heldt JP, Spengler NM, Nicolay LI, Ruckle HC, Koning JL, Millard WW 2nd, Jin DH, Baldwin DD

J Urol. 2009 Dec;182(6):2762-7
doi:10.1016/j.juro.2009.08.042

References:

1Brenner, D. J. and Hall, E. J.: NEJM: 357: 2277, 2007
2Health Risks from Exposure to Low Levels of Ionizing Radiation. Nat'l Research Council. National Academies Press 2005
3Ferrandino, M. N., Bagrodia, A., et al.: J. Urol. 181: 668, 2009.
4Kluner, C., Hein, P. A., et al. J. Comput. Assist. Tomogr. 30: 44, 2006
5Niemann, T., Kollmann, T., et al.: AJR Am. J. Roentgenol. 191: 396, 2008.

Written by UroToday.com Medical Editor Ralph V. Clayman, MD

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