Factors affecting patient radiation exposure during percutaneous nephrolithotomy

Abstract

Purpose: We identified patient and stone characteristics that may contribute to increased radiation exposure during percutaneous nephrolithotomy and offer technique modifications to limit the radiation dose.

Material and methods: We reviewed the records of 96 patients who underwent percutaneous nephrolithotomy in the last 2 years. The effective radiation dose was calculated using accepted conversion tables. We performed multivariate linear regression to determine the association of the effective radiation dose with specific patient, stone and procedural characteristics.

Results: Mean±SD patient age was 51.5±13.4 years and 62.5% of the patients were female. Median body mass index was 32.0±9.7 kg/m2 (range 16.2 to 59.6) and the median stone burden was 4 cm2. Increased body mass index (p<0.001), higher stone burden (p=0.013), stone nonbranched configuration (p=0.002) and a greater number of percutaneous access tracts (p=0.040) were significantly associated with an increased effective radiation dose. Specifically obese patients with a body mass index of 30 to 39.9 kg/m2 had a more than 2-fold increase in the mean adjusted effective radiation dose and morbidly obese patients with a body mass index of 40 kg/m2 or greater had a greater than 3-fold increase vs that in normal weight patients with a body mass index of less than 25 kg/m2 (6.49 and 9.13 mSv, respectively, vs 2.66, p<0.001). Other stone specific parameters, including site and composition, percutaneous access site and estimated blood loss were not associated with the effective radiation dose.

Conclusions: Patients with higher body mass index, greater stone burden, nonbranched stones and multiple nephrostomy access tracts are at risk for increased radiation exposure during percutaneous nephrolithotomy. Urologists must seek alternative strategies to minimize radiation exposure, such as tighter collimation to the region of interest, judicious use of magnification and the acquisition of as few images as possible during stone removal.