Radiation dose for pedicle screw insertion. Fluoroscopic method versus computer-assisted surgery.

STUDY DESIGN: Comparison of the radiation dose between the traditional fluoroscopic approach and computed tomography (CT)-based computer-assisted surgery for pedicle screw placement was determined.

OBJECTIVES: To evaluate the radiation dose delivered by fluoroscopy-controlled pedicle screw placement versus insertion guided by computer. To define the CT computer-assisted protocol, involving lower radiation exposure for the patient, that still provides acceptable image quality.

SUMMARY OF BACKGROUND DATA: There are no published data describing the dose delivered in CT-based image-guided surgery, and there are few studies in which the organ dose and the effective dose delivered during pedicle screw insertion that is performed traditionally with fluoroscopic control are described.

METHODS: Dose measurements were performed on two types (REMAB and RANDO) of anthropomorphic phantoms. Thermoluminescent dosimeters were used to measure the organ dose. Both phantoms were exposed to the fluoroscopic x-ray beam. The representative intraoperative scenario was determined by observation of 20 consecutive surgical interventions featuring pedicle screw implantation. For the CT dose measurement only, the REMAB phantom was used with two types of CT scanners. Three scanning protocols were evaluated: sequential, spiral optimized, and sequential optimized. Optimization of the scanning protocol included changes of anode current. The CT images were subsequently processed to achieve three-dimensional reconstruction of the lumbar spine for the computer-assisted intervention.

RESULTS: Organ and effective doses were higher in any of the CT examinations than in the fluoroscopic procedure. There was a slight difference between doses registered during optimized spiral scanning and doses in the calculated optimized sequential CT protocol. Optimized sequential scanning was associated with an effective dose 40% lower than that in nonoptimized sequential scanning. The small anatomic structures of the spine could be easily recognized on each of the three-dimensional reconstructions, and all of them were suitable for use in computer-assisted surgery.

CONCLUSIONS: Percutaneous pedicle screw insertion in the lumbar region of the spine, performed using fluoroscopic control, requires a lower radiation dose than do CT scans necessary for computer-assisted surgery. The CT radiation dose can be significantly decreased by optimization of the scanner settings for computer-assisted surgery. The advantages of computer-assisted surgery justify CT scans, when based on correctly chosen indications.