Indeed, in one article, it was estimated that the ionizing radiation from CT scans in 2007 could lead to as many as 29,000 future cancers.1 This observation has created across the medical spectrum an increased scrutiny of radiation doses from a wide range of radiographic studies.
In the present study of 96 patients undergoing percutaneous nephrostolithotomy (PCNL), the authors noted that the following factors all resulted in increased radiation exposure: increasing stone burden, a nonbranched stone, and use of more than one nephrostomy tract. However, none of these were as significant as body mass index (BMI). For patients with a BMI under 25, the estimated radiation dose was only 2.7 mSv whereas for patients at 25-29.9 BMI, 30-30.9 BMI, and ≥40BMI, the radiation dose rose to 5.4, 6.5, and 9.1 mSv respectively. The latter two levels are equivalent to a full body CT scan.
When taken in isolation, this amount of radiation does not appear to be overly disconcerting; however, when put into the full context of a patient with urolithiasis, the total radiation dose received in the same year as an acute stone episode can average as much as 30 mSv.2 In this same cited study, in 20% of the cases, the total radiation dose exceeded 50 mSv which is the maximum exposure allowed by the International Commission on Radiation Protection for 1 year (N.B. – 5 yr. maximum is 100mSv).2
There are several ways in which the radiation exposure during PCNL can be reduced. The easiest maneuvers are to use last image hold, avoid magnification, use pulsed fluoroscopy (especially digital imaging at only 15 frames/second), and collimate the image whenever possible. Also the image intensifier should be as close to the patient’s back as possible and at all times, the “on-off” fluoroscopy pedal should be under the control of the surgeon.
One final observation made by the authors is worth stressing. Urolithiasis and cancer are both more common in the obese population. As such, for obese patients presenting with large stones requiring PCNL, limiting radiation exposure may be of even greater importance than in the lower risk non-obese population.
References:
- Berrington de Gonzalez, A., Mahesh, M., Kim, K.P. et al. Projected cancer risks from computed tomographic scans performed in the Untied States in 2007. Arch. Intern Med. 169: 2071, 2009.
- Ferrandino, M. N., Bagrodia, A., Pierre, S. A., et al.: Radiation exposure in the acute and short-term management of urolithiasis at 2 academic centers. J. Urol. 181: 668, 2009.
J Urol. 2010 Dec;184(6):2373-7
10.1016/j.juro.2010.08.033
PubMed Abstract
PMID: 20952034
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