CUA 2018: Minimizing Ionizing Radiation Exposure During Retrograde Fluoroscopic Guided Ureteral Stent Insertion in the Pregnant Patient

Halifax, Nova Scotia ( Management of urolithiasis and establishing a definitive diagnosis during pregnancy poses a significant challenge to urologists. Symptomatic stone events are associated with preterm rupture of membranes, preterm labor, and mild pre-eclampsia. Ultrasonography is the 1st line imaging modality for the diagnosis of urolithiasis in pregnant patients. However, when intervention is required to resolve the renal colic, ultrasonography may be suboptimal and often fluoroscopy is used to navigate and guide the procedure. Although fluoroscopy is most optimal imaging modality for ureteroscopy or percutaneous nephrolithotomy, it is associated with significant ionizing radiation to the patient. This matter becomes even more important for patients during pregnancy. The risk of congenital malformations associated with radiation exposure has been extensively studied and published. 

Mohammad Mohaghegh, MD, and colleagues reported a study where they examined the effect of shielding, collimation and different fluoroscope settings on radiation exposure to the mother and fetus during an X-ray guided retrograde ureteric stent insertion. Authors assembled a phantom using methyl methacrylate to mimic a pregnant patient undergoing a fluoroscopic procedure (Figure 1). A standard 20cc syringe, containing 15cc of Omnipaque contrast agent at 50% concentration was used to mimic renal collecting system. Dose measurements were carried out at the fetal location with no shielding used, fetal location shielded, beam collimated to avoid fetal location and adjacent to the kidney with fetal location shielded. Measurements were taken for all four combinations with normal or low-dose fluoroscopy modes and continuous or pulsed fluoroscopy modes. 

Figure 1
UroToday CUA 2018 Minimizing Ionizing Radiation Exposure 1

Mohaghegh presented that minimal fetal doses is achieved when the beam is collimated such that the fetus is completely outside of the irradiated field of view, with a reduction in fetal dose of almost 90% relative to the situation where the fetus is within the field of view. Shielding the fetus with 0.5mm lead equivalent thyroid shield reduced fetal dose by roughly 70% while increasing exposure to mother by roughly 40%. While using low dose instead of normal fluoroscopy, and pulsed instead of continuous fluoroscopy, provides significant dose sparing to both the mother and the fetus. 

Figure 2
UroToday CUA 2018 Minimizing Ionizing Radiation Exposure 2

Mohaghegh concluded that using pulsed dose fluoroscopy with collimation is the most effective fluoroscopy setting to minimize radiation exposure to the fetus. Additionally, shielding with thyroid collars while reducing dose to the shielded area increases exposure to the tissue surrounding the shielded area.

Presented by: Mohammad Mohaghegh, MD, Harry Ingleby, and Brian Peters, Section of Urology, University of Manitoba. 

Written By: Zhamshid Okhunov (Twitter: @OkhunovZham), (Department of Urology, University of California-Irvine) medical writer for at the 73rd Canadian Urological Association Annual Meeting - June 23 - 26, 2018 - Halifax, Nova Scotia