The use of active fluoroscopy for spinal instrumentation

Transcription

1 J Neurosurg Spine 19: , 2013 AANS, 2013 Operating room radiation exposure in cone beam computed tomography based, image-guided spinal surgery Clinical article Eric W. Nottmeier, M.D., 1 Stephen M. Pirris, M.D., 1 Steven Edwards, A.R.N.P., 1 Sherri Kimes, A.R.N.P., 1 Cammi Bowman, R.N., M.S.N., 1 and Kevin L. Nelson, Ph.D. 2 Departments of 1 Neurosurgery and 2 Radiology, Mayo Clinic, Jacksonville, Florida Object. Surgeon and operating room (OR) staff radiation exposure during spinal surgery is a concern, especially with the increasing use of multiplanar fluoroscopy in minimally invasive spinal surgery procedures. Cone beam computed tomography (cbct) based, 3D image guidance does not involve the use of active fluoroscopy during instrumentation placement and therefore decreases radiation exposure for the surgeon and OR staff during spinal fusion procedures. However, the radiation scatter of a cbct device can be similar to that of a standard 64-slice CT scanner and thus could expose the surgeon and OR staff to radiation during image acquisition. The purpose of the present study was to measure radiation exposure at several unshielded locations in the OR when using cbct in conjunction with 3D image-guided spinal surgery in 25 spinal surgery cases. Methods. Five unshielded badge dosimeters were placed at set locations in the OR during 25 spinal surgery cases in which cbct-based, 3D image guidance was used. The cbct device (O-ARM) was used in conjunction with the Stealth S7 image-guided platform. The radiology department analyzed the badge dosimeters after completion of the last case. Results. Fifty high-definition O-ARM spins were performed in 25 patients for spinal registration and to check instrumentation placement. Image-guided placement of 124 screws from C-2 to the ileum was accomplished without complication. Badge dosimetry analysis revealed minimal radiation exposure for the badges 6 feet from the gantry in the area of the anesthesiology equipment, as well as for the badges located feet from the gantry on each side of the room (mean mrem/spin). The greatest radiation exposure occurred on the badge attached to the OR table within the gantry (mean mrem/spin), as well as on the control panel adjacent to the gantry (mean mrem/spin). Conclusions. Radiation scatter from the O-ARM was minimal at various distances outside of and not adjacent to the gantry. Although the average radiation exposure at these locations was low, an earlier study, undertaken in a similar fashion, revealed no radiation exposure when the surgeon stood behind a lead shield. This simple precaution can eliminate the small amount of radiation exposure to OR staff in cases in which the O-ARM is used. ( Key Words image guidance computer-assisted surgery navigation cbct radiation exposure spinal fusion The use of active fluoroscopy for spinal instrumentation placement can result in radiation exposure for the surgeon and OR staff. 3,17,23 In minimally invasive spinal fusion procedures, the use of multiplanar fluoroscopy for the placement of percutaneous pedicle screws probably increases radiation exposure for the surgeon. 2 As minimally-invasive spinal procedures become more popular, radiation exposure for the surgeon and OR staff may increase. Abbreviations used in this paper: BMI = body mass index; cbct = cone beam CT; HD3D = high-definition 3D; OR = operating room. Accurate instrumentation placement in the cervical, thoracic, and lumbar spine has been reported with the use of 3D image guidance. 5,6,12 14,16,24 A theoretical advantage of 3D image guidance is decreased radiation exposure for the surgeon and OR staff. A reduction in surgeon radiation exposure when utilizing 3D image guidance for spinal instrumentation placement has been reported in several in vitro studies. 4,8,19,21,22 A standard CT scanner can emit radiation to the surrounding environment when images are acquired. 7,10 Additionally, a cbct device can have radiation scatter similar to that of a standard 64-slice CT scanner. 26 In a recent in vivo study, we reported that no surgeon radiation exposure occurred in cbct-based, 226 J Neurosurg: Spine / Volume 19 / August 2013

2 Radiation exposure in cbct-based, image-guided spinal surgery 3D image-guided spinal surgery when the surgeon stood behind a lead shield in the OR during cbct acquisition. 11 In the current study, radiation exposure at several unshielded locations in the OR was measured in 25 spinal surgery cases utilizing cbct-based, 3D image guidance. Methods Institutional review board approval was obtained. Five badge dosimeters were placed at set locations in the OR during 25 spinal surgery cases in which cbct-based, 3D image guidance was used (Fig. 1). The radiation dosimeters used in this study were obtained from Mirion Technologies, Inc. The TLD 760 (thermoluminescent dosimeter) is designed to respond to beta, gamma, x-ray, and neutron radiation. Through internal filters contained in the dosimeter, the radiation quantity and quality can be determined. The dosimeters were placed to avoid directional dependence. Results from the vendor are reported for deep, eye, and shallow doses. In our study, the quality of the accumulated scatter radiation was of sufficient energy so that the deep, eye, and shallow doses were roughly equivalent to each other for each individual dosimeter. Distance and height measurements for the individual badges are listed in Table 1. Distance was measured from the center of the OR table, and height was measured from the floor. The cbct device used in this study was the O-ARM (Medtronic, Inc.), used in conjunction with the Stealth S7 image-guided platform (Medtronic, Inc.). The O-ARM was used for registration of the spinal anatomy after the spine was exposed in open cases and after placement of the percutaneous reference TABLE 1: Distance and height measurements of 5 badge dosimeters in the OR during 25 cbct-based, image-guided spinal surgery cases Badge Distance From Gantry Center (ft) Height From Floor (ft) arc in minimally invasive cases. Anteroposterior (AP) and lateral (Lat) fluoroscopic scout views of the spine were accomplished using the O-ARM to aid in positioning the device in the appropriate location around the patient. In most cases, 1 O-ARM spin was able to register the levels of interest; however, in long-level fusions, 2 or 3 spins were required. The O-ARM has different protocols and settings that can be selected to maximize image quality. The protocols that can be chosen are head, chest, and abdomen. Within each protocol, settings are selected based on patient size: small, medium, large, and extra large. In addition, the actual cbct spin can be set in standard or high definition 3D mode. High-definition 3D cbct spins were accomplished in all cases. The head protocol was used in fusion procedures involving the upper and midcervical spine. The chest protocol was used in fusions involving the thoracic spine. In lumbar fusion cases, the abdomen protocol was used. Patient size determined the fur- Fig. 1. Illustration depicting the OR setup and location of the dosimetry badges when performing a cbct spin. Numbers in the figure represent the location of each badge dosimeter. Modified with permission from Nottmeier et al.: Int J Med Robotics Comput Assist Surg 2012; 8: ; DOI: /rcs , John Wiley & Sons, Ltd. J Neurosurg: Spine / Volume 19 / August

3 E. W. Nottmeier et al. ther settings that were chosen on the spectrum from small to extra large. In general, the small setting was used in patients with a BMI < 25. In patients with a BMI of 26 30, the medium setting was used. The large setting was used in patients with a BMI of 31 35, and the extra large setting was used in patients with a BMI > 35. Prior to wound closure, another O-ARM spin was accomplished to check instrumentation placement (confirmatory spin). After the 25th case, the badge dosimeters were sent to the radiology department for analysis. In 9 cases the O-ARM registration process was timed. This registration process included the tasks of placing the reference arc on the patient, draping the patient, positioning the O-ARM, performing the cbct scan, removing the O-ARM, and undraping the patient. Timing was initiated when the surgeon asked for the reference arc and was stopped when the image-guided system was ready for navigation of the patient s spine. Results Overall, 50 HD3D cbct spins were accomplished in 25 patients (Table 2). One hundred twenty-four screws were placed into spinal levels spanning from C-2 to the ileum. The mean BMI for the 25 patients in this study was No complications resulted from instrumentation placement or the use of image guidance. Badge dosimetry data are listed in Table 3. Analysis of the badge dosimeters revealed minimal radiation exposure for the badges 6 feet from the gantry in the area of the anesthesiology equipment, as well as for the badges located feet from the gantry on each side of the room (mean mrem/spin). The highest radiation exposure occurred on the badge attached to the OR table within the gantry (mean mrem/spin), as well as on the control panel adjacent to the gantry (mean mrem/spin). The average time to perform the registration process in the 9 timed cases was 6 minutes 26 seconds. Discussion The use of active fluoroscopy as an adjunct to spinal instrumentation placement is relatively common. Accordingly, seconds of fluoroscopy time per screw is the TABLE 2: Summary of data in 25 patients undergoing spinal surgery using cbct-based, 3D image guidance* Case No. Age (yrs) BMI Diagnosis Procedure No. of cbct Spins postlaminectomy instability L4 5 TLIF L-2 fracture above L3 S1 PSF extension of PSF to T chronic pain syndrome implantation of morphine pump (image- 1 guided placement of intrathecal catheter through fusion mass) L5 S1 degenerative tilt w/ radiculopathy L5 S1 TLIF adjacent segment fusion disease extension of L2 5 PSF to S adjacent segment fusion disease extension of L1 5 PSF to S discogenic back pain L5 S1 MI TLIF pseudarthrosis revision L2 4 PSF osteomyelitis L2 5 PSF pseudarthrosis revision L4 5 PSF spondylolisthesis L3 4 PSF spondylolisthesis L5 S1 PSF adjacent segment fusion disease extension of PSF to L thoracic kyphosis, sagittal imbalance T11 ileum PSF, L-2 PSO multilevel cervical stenosis w/ myelopathy C2 T1 PSF cervical stenosis due to osteophytic spur ACDF C L4 5 spondylolisthesis L4 5 MI TLIF rt SI joint instability due to previous osteomyelitis rt SI joint fusion L4 5 spondylolisthesis w/ multilevel lumbar stenosis L3 S1 PSF sacral tumor, degenerative scoliosis excision of sacral tumor, L4 S1 PSF cervical kyphotic deformity C-4 corpectomy, C2 T1 PSF discogenic back pain L5 S1 MI TLIF rt SI joint instability due to previous osteomyelitis rt SI joint fusion L1 2 bony foraminal stenosis L-1 & L-2 far lat foraminotomy L4 5 spondylolisthesis L4 5 MI TLIF 2 * ACDF = anterior cervical discectomy and fusion; MI = minimally invasive; PSF = posterior spinal fusion; PSO = pedicle subtraction osteotomy; SI = sacroiliac; TLIF = transforaminal lumbar interbody fusion. 228 J Neurosurg: Spine / Volume 19 / August 2013

4 Radiation exposure in cbct-based, image-guided spinal surgery TABLE 3: Summary of badge dosimetry data in 25 spinal surgery cases utilizing cbct* Badge Badge Dosimetry Reading After 50 cbct Spins range reported in the literature. 8,15,18 20 Disadvantages to the surgeon in using active fluoroscopy for pedicle screw placement include wearing a lead apron and the ergonomic challenge of working around the fluoroscope. 4 In addition, spinal surgeons can sustain a 10- to 12-fold increase in radiation exposure as compared with surgeons using fluoroscopy for nonspinal procedures. 17 In a prospective study measuring surgeon radiation exposure in transforaminal lumbar interbody fusion procedures, Bindall et al. 2 reported a mean fluoroscopy time of 1.69 minutes per case, with a mean radiation exposure to the surgeon s torso (under a lead apron) of 27 mrem per case. Subsequently, Bindall et al. 2 concluded that the recommended maximum allowed annual radiation exposure of 5 rem to the torso might be exceeded if a surgeon performed more than 194 of these procedures annually. The use of cbct-based image guidance for percutaneous pedicle screw placement has been reported. 1,12,25 Obviously, the surgeon is not exposed to radiation during screw placement in open or minimally invasive cbct-based, image-guided spinal surgery, as the surgeon is navigating from the intraoperative cbct scan, and no active fluoroscopy is used. However, scatter radiation is emitted in the OR during cbct acquisition, and this can result in radiation exposure to the surgeon and OR staff. In a study measuring radiation scatter, Zhang et al. 26 reported that the O-ARM and a 64-slice CT scanner have similar radiation scatter that can extend to distances up to 6 m (19.7 feet) from the device. At our institution, OR staff either stand behind a lead shield or vacate the room when the cbct spin is performed. We have previously demonstrated that no radiation exposure occurs when standing in the OR behind a lead shield during a cbct spin. 11 However, instances may arise when the surgeon or OR staff are temporarily unshielded during a cbct spin, and our present study demonstrates that scatter radiation exposure at distances > 6 feet from the cbct gantry in these circumstances is relatively low. For example, the mean radiation dose per spin at the location of Badge 1 was 3.6 mrem/spin. Accordingly, a person standing unshielded in this position would exceed the recommended annual limit of 5 rem to the torso as set forth by the National Council on Radiation Protection and Measurements 9 after 1381 cbct spins. During cbct-based image guidance procedures, the patient is exposed to radiation. Measurements from the badge dosimeter placed on the OR table within the cbct gantry in our study showed an average radiation exposure J Neurosurg: Spine / Volume 19 / August 2013 Mean Radiation Dose per Spin * Values expressed in mrem. of 177 mrem per cbct spin. It should be noted, however, that this badge dosimeter was placed on the OR table adjacent to the patient and not in the center of the cbct gantry. Hence, the badge dosimeter reading underestimates the true patient radiation exposure. Additionally, using the badge dosimeter is a crude method of measuring patient radiation exposure, and true assessment utilizes more advanced methods, including phantom models and ion chambers. 26 These methods are out of the scope of the present study, which was focused on cbct scatter radiation exposure in the OR, and not on patient radiation exposure. A full detailed analysis of patient radiation exposure from the O-ARM using these advanced methods has been accomplished and demonstrates that exposure during 1 spin of the O-ARM is equal to approximately 47% 83% of the patient radiation exposure sustained by a scan from a 64-slice CT scanner, depending on the specific protocol used. 26 A 3-fold increase in effective radiation dose to the patient can occur when using the extra large setting as compared with the small setting on the O-ARM, since larger patients require more radiation to visualize their bony anatomy during cbct scanning. We believe that this patient radiation exposure is acceptable, as it is well below the recommended annual limit of 5 rem to the torso as set forth by the National Council on Radiation Protection and Measurements. 9 Although patient radiation exposure must always be considered in spinal fusion procedures, radiation exposure for the surgeon and OR staff is a significant consideration given that the patient will most likely only undergo 1 spinal fusion that year, whereas the surgeon and OR staff may participate in 100 or more spinal fusion procedures per year, depending on the hospital and surgeon practice. To further decrease patient radiation exposure, we have modified our practice based on information learned in performing the current study. In our typical protocol, we have used the HD3D mode for all of our O-ARM spins. Using the standard 3D mode can decrease patient radiation exposure by 40%, and we have found that this mode is sufficient to visualize the spinal anatomy in cervical and lumbar cases if spinal instrumentation artifact is not present, even in obese and osteoporotic patients. Additionally, we have noticed that the standard 3D mode is sufficient when used in patients with implantable intrathecal pumps located in the abdominal subcutaneous tissue away from the spine but within the field of the O-ARM spin (Fig. 2). Consequently, we now use the standard 3D mode for registration O-ARM spins in the cervical and lumbar spine. Note that the upper thoracic spine anatomy can be difficult to visualize in some patients with broad shoulders; therefore, we continue to use HD3D mode for registration in these patients. The time required for the process of spinal registration using the O-ARM in this study was less than 7 minutes, which included the HD3D mode image acquisition time of 26 seconds. Another advantage of using the standard 3D mode is that the spin takes half as long (13 seconds) as compared with a spin in the HD3D mode. Conclusions Radiation scatter from the O-ARM was low at vari- 229

5 E. W. Nottmeier et al. Fig. 2. A: Anteroposterior radiograph showing an intrathecal pump and osteopenia in a patient set to undergo L5 S1 fusion using the O-ARM. B and C: Screenshots from the image-guided system showing adequate image quality for navigation using the standard 3D mode on the O-ARM. ous distances outside of and not adjacent to the gantry. Accordingly, OR staff that occasionally become unshielded at these distances are most probably not going to sustain significant radiation exposure. Although the average radiation exposure at these locations is low, we continue to advocate that OR staff fully shield themselves during O- ARM spins, as we have previously demonstrated that no radiation exposure occurs in these circumstances when standing behind a lead shield. 11 Disclosure Dr. Nottmeier is a consultant for Depuy/Synthes Spine, Medtronic Navigation, Globus Spine, and K2M. Author contributions to the study and manuscript preparation include the following. Conception and design: Nottmeier, Pirris, Bowman, Nelson. Acquisition of data: Nottmeier, Pirris, Edwards, Kimes, Bowman. Analysis and interpretation of data: all authors. Draf ting the article: Nottmeier, Nelson. Critically revising the ar - ticle: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Nottmeier. Administrative/technical/material support: Ed wards, Kimes, Bowman. Study supervision: Nottmeier. Acknowledgments The authors thank Alice McKinney for her illustration and Paul Brickwood for his assistance with intraoperative image guidance. References 1. Acosta FL Jr, Thompson TL, Campbell S, Weinstein PR, Ames CP: Use of intraoperative isocentric C-arm 3D fluoroscopy for sextant percutaneous pedicle screw placement: case report and review of the literature. 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6 Radiation exposure in cbct-based, image-guided spinal surgery nolly PJ: Electromagnetic field-based image-guided spine surgery part two: results of a cadaveric study evaluating thoracic pedicle screw placement. Spine (Phila Pa 1976) 28:E351 E354, Slomczykowski M, Roberto M, Schneeberger P, Ozdoba C, Vock P: Radiation dose for pedicle screw insertion. Fluoroscopic method versus computer-assisted surgery. Spine (Phila Pa 1976) 24: , Smith HE, Welsch MD, Sasso RC, Vaccaro AR: Comparison of radiation exposure in lumbar pedicle screw placement with fluoroscopy vs computer-assisted image guidance with intraoperative three-dimensional imaging. J Spinal Cord Med 31: , Tannoury T, Crowl AC, Battaglia TC, Chan DP, Anderson DG: An anatomical study comparing standard fluoroscopy and virtual fluoroscopy for the placement of C1-2 transarticular screws. J Neurosurg Spine 2: , Ul Haque M, Shufflebarger HL, O Brien M, Macagno A: Radiation exposure during pedicle screw placement in adolescent idiopathic scoliosis: is fluoroscopy safe? Spine (Phila Pa 1976) 31: , Verma R, Krishan S, Haendlmayer K, Mohsen A: Functional outcome of computer-assisted spinal pedicle screw placement: a systematic review and meta-analysis of 23 studies including 5,992 pedicle screws. Eur Spine J 19: , Villavicencio AT, Burneikiene S, Bulsara KR, Thramann JJ: Utility of computerized isocentric fluoroscopy for minimally invasive spinal surgical techniques. J Spinal Disord Tech 18: , Zhang J, Weir V, Fajardo L, Lin J, Hsiung H, Ritenour ER: Dosimetric characterization of a cone-beam O-arm imaging system. J XRay Sci Technol 17: , 2009 Manuscript submitted July 28, Accepted April 23, Portions of this work were presented in abstract form at the 65th Annual Meeting of the Neurosurgical Society of America held in Park City, Utah, on June 13, Please include this information when citing this paper: published online May 31, 2013; DOI: / SPINE Address correspondence to: Eric W. Nottmeier, M.D., Department of Neurosurgery, Mayo Clinic Jacksonville, 4500 San Pablo Road, Jacksonville, Florida nottmeier.eric@mayo. edu. J Neurosurg: Spine / Volume 19 / August