Usefulness of Unilateral X-ray of the Kidney, Ureter, and Bladder in the Follow-up of Patients Treated with Extracorporeal Shock Wave Lithotripsy: Reduction of Radiation Exposure

Kim, Yeong Il; Kim, Tae Kyu

Abstract

PURPOSE: The objective of this study was to assess the usefulness of a unilateral x-ray of the kidney, ureter and bladder (hemi-KUB), in the place of a full-KUB, in the follow-up of patients treated with extracorporeal shock wave lithotripsy (ESWL), and thereby reduce the radiation exposure for patients.
MATERIALS AND METHODS
A total of 111 patients, who underwent ESWL, between March 2000 and July 2002, were enrolled onto the study. Patients with bilateral stones, or who had changed to another treatment model, were excluded. During the follow-up to the ESWL, we used the hemi-KUB method for the collimation of the radiation field. The numbers of hemi-KUBs during the treatment were recorded. The reductions in the exposure to the radiation dose, per patient, were calculated and analyzed according to the sizes and shapes of the stones. The typical doses were: for IVU (6 films), 2.5mSv; full-KUB film, 0.42mSv; and a hemi-KUB film, 0.21mSv.
RESULTS
The total reduction in the doses of radiation exposure was 114.45mSv. The radiation doses, per patient, were reduced by a mean of 1.03+/-0.58mSv. The reduction in the dose of radiation exposure correlated well with the stone size (r=0.7082, p<0.05). The mean number of hemi-KUBs (mean reduction dose of radiation exposure), according to the stone size groups: these being 5-9, 10-19 and +/-20mm, were 3.82+/-1.76 (0.80+/-0.37), 6.52+/-2.10 (1.37+/-0.44) and 11.00+/-3.85 (2.31+/-0.81)mSv, respectively (p<0.05). Also, the mean number of hemi-KUBs (mean reduction dose of radiation exposure), according to the stone shapes, typed into I (less organized or lacy), IIa (spiculated), IIb (mulberry), III (round or ovoid) and IV (struvite or staghorn), were 2.77+/-0.85 (0.58+/-0.18), 4.48+/-1.86 (0.94+/-0.39), 4.83+/-1.43 (1.01+/-0.30), 7.54+/-1.36 (1.58+/-0.29) and 8.75+/-3.72 (1.84+/-0.78)mSv, respectively (p<0.05). Using the receiver operating characteristic curve, the cut-off value, of a stone size that could be used to determine the risk group whose radiation exposure exceeding 5mSv (personal permissible dose/year), was 23.52mm, but when using a full-KUB this was 7.97mm.
CONCLUSIONS
The use of hemi-KUB is a simple and easy method to reduce the radiation exposure in the follow-up of an ESWL, especially in patients with stones larger than 7.97mm in size, with a round-ovoid or staghorn shape.