Fetal dose estimation during live fluoroscopy using a real-time staff dosimetry system.
Morrison C, and Vanderhoek M. Fetal dose estimation during live fluoroscopy using a real-time staff dosimetry system. Med Phys 2018; 45(6):e136.
Purpose: Estimates of fetal dose can be challenging for fluoroscopicallyguided interventions (FGI) involving pregnant patients since the fetus is typically exposed only to scatter radiation. Furthermore, the fetal dose estimate is available only AFTER, rather than DURING, the procedure. We investigated a method to estimate the fetal dose both during and after FGI using a realtime staff dosimetry system. Methods: During hepatic FGI, two solid-state dosimeters (RaySafe i2, Unfors RaySafe, Billdal, Sweden) were placed on the x-ray beam entrance side and beam exit side of pregnant patients at the level (in the inferior-superior direction) of the fetus. The fetus and the dosimeters were not in the primary x-ray beam. For each dosimeter, the instantaneous dose rate and cumulative dose were displayed in real time to interventional staff. This dose data, coupled with scatter depth-dose curves, were used to estimate fetal dose. For a typical FGI setup, scatter depth-dose curves were obtained by measuring the scatter dose rate at multiple depths in a 30 cm thick acrylic phantom at various distances from the edge of the primary beam. Results: Scatter depth-dose curves demonstrated similar shape regardless of the distance from the edge of the primary beam, with maximum scatter dose occurring at a depth of 5-6 cm from the beam entrance surface. On average, the fetal dose was 30% of the entrance scatter dose and 500% of the exit scatter dose. Fetal dose was estimated in four patients. Fetal dose estimates using the dosimeters on the beam entrance and beam exit sides differed by less than 10%. Conclusion: Fetal dose can be estimated during FGI using real-time dosimeters along with scatter depth-dose curves. Real time estimates of fetal dose may enable interventional staff to better optimize their use of the fluoroscopy system during FGI in order to minimize fetal dose.