In automated fluoroscopy settings, does shielding affect radiation exposure to surrounding unshielded tissues?

BACKGROUND AND PURPOSE: Automatic brightness control (ABC), a function of modern fluoroscopy machines, adjusts radiation intensity in real time to enhance image quality. While shielding reduces radiation exposure to protected areas, it is unknown how much radiation adjacent unshielded areas receive when using ABC settings. Our purpose was to assess radiation dosage to shielded and unshielded tissue when using fluoroscopic ABC mode compared with fixed exposure settings.

MATERIALS AND METHODS: In a simulated ureteroscopy, thermoluminescent dosimeters (TLDs) were placed at three sites in a female human cadaver, including the right renal hilum, right distal ureter adjacent to the uterus, and directly over the uterus. The cadaver received 60 seconds of radiation exposure using a C-arm fluoroscopy system under ABC and fixed settings (1.38 mAs, 66 kVp) with and without uterine shielding. Radiation dosage absorbed by the TLDs was compared using two-way analysis of variance and least-squares confidence intervals.

RESULTS: Shielding significantly reduced radiation dose to the uterus by 62% and 82% (P<0.05 for both) in ABC and fixed settings, respectively. Shielding of the uterus in ABC, however, resulted in an approximately twofold increase in radiation dosage to the ureter and ipsilateral kidney (P<0.05 for both) and a decrease in image quality. Using fixed settings, shielding of the uterus did not increase radiation dose to the ipsilateral ureter and kidney.

CONCLUSION: There is a significant increase in radiation dosage to surrounding tissues when shielding is used with ABC mode during fluoroscopy. Radiation can be reduced and image quality improved by using fixed settings when shielding is indicated.