Letter to the Editor: Richerand et al, J Pediatr Orthop. 2016;36:530–533
We read with interest the recent publication by Richerand et al, “Comparison of effective Dose of Radiation During Pedicle Screw Placement Using Intraoperative Computed Tomography Navigation Versus Fluoroscopy in Children With Spinal Deformities.” In the discussion, the authors refer to “adjustment of computed tomography (CT) parameters to achieve the lowest radiation level possible without compromising the quality of images.” Could the authors elaborate on what settings were used on the intraoperative CT scanner for this series and, specifically, the weight-based settings?
Our group has used the protocol developed by Ohlin et al in patients up to 70 kg with 80 kV, 20 mA, 80 mAs1,2 with an estimated 0.65 mSv per scan, and Vishal Sarwahi et al reported on a similar low dose protocol resulting in 0.68 mSv per scan (SRS Annual Meeting, 2016). It seems that the settings in your series used on the CT scanner must be much higher for the patients with increased body mass index.
Also, how many seconds of fluoroscopy time were used in this study and what was the DAP? Previous studies have reported that fluoroscopy time for spinal instrumentation ranges from 63 to 126 seconds per screw placed or 1.0 to 1.52 mSv per patient with a mean of 5 pedicle screws placed.3,4 Understandably, fluoroscopy time has a significant impact on fluoroscopy dose. Further, posteroanterior versus lateral fluoroscopy also has a significant impact on dosing.5 We calculated that 1 low dose 80-20-80 O-arm spin was equivalent to 80 seconds of fluoroscopy time.5 Could you provide a similar conversion based on your study results? This allows for surgeons to look critically at their fluoroscopy time and compare the value of fluoroscopy to the 3-dimensional value of a low-dose CT scan.
Finally, did you consider the role of intraoperative radiographs? Surgeons using the freehand technique with intraoperative radiographs should take into account the dosing of intraoperative radiographs since filters and biplanar slot scanning technology are not typically available intraoperatively. At our center, intraoperative posteroanterior and lateral films impart 0.83 mSv of radiation (more than an intraoperative low-dose CT).
We welcome further discussion on this important topic. It is helpful to have these data made readily available to surgeons who can best discern the appropriate strategy for their practice.