Response to the Letter From Dr Noelle Larson et al Regarding Our 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”

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In Reply:
Dear Dr Hensinger, This is our response to the letter from Dr Noelle Larson et al regarding our 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.” I have restated questions in the letter and bolded our responses.
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?
We adjust the MA and KV on the O-Arm to have the lowest radiation exposure possible based on our previous settings while attaining images of acceptable quality. We measure the patient in the thoracic and lumbar area when the patient is placed prone. On the basis of the patient’s weight and the thickness measured, the mA and kV are chosen. For example, for a 50 kg patient, our technicians would choose 16 mA, 70 kV, and 63 mAs for the O-Arm settings.
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.
For patients with higher weights, we increase the settings on the O-Arm to maintain acceptable image quality.
Also, how many seconds of fluoroscopy time were used in this study and what was the dose area product?
We use 30 to 120 seconds of fluoroscopy time per case on average. This time varies based on the technique of pedicle screw placement. We did not calculate the dose area product for each fluoroscopy case.
We calculated that 1 low dose 80-20-80 O-arm spin was equivalent to 80 seconds of fluoroscopy time. Could you provide a similar conversion based on your study results?
The dose for a certain total fluoroscopy time depends on the field size(s) used, the size of the patient, and the body region. Similarly for the O-arm spins. We estimated our population sample dose distribution for fluoroscopic exposures to different body regions, patient sizes, and field sizes. We also estimated our population sample dose for O-Arm spins to different body regions and patient sizes. We are not able to convert O-Arm spin doses to fluoroscopy time in seconds.
Finally, did you consider the role of intraoperative radiographs?
We did not routinely use intraoperative radiographs.
We would like to thank the authors of the letter for their thoughtful questions and their interest in our article.

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