Research Article
Comparison of Intraoperative Radiation Exposure for O-Arm Intraoperativect vs. C-Arm Image Intensifier in Minimally Invasive Lumbar Fusion
Chong Hing Wong1*#, Yoshihisa Kotani2*#, Junichi Tochio3, Hiromitsu Takeda4, Masamoto
Takano3 and Norimasa Iwasaki5
1Department of Orthopedics and Traumatology, Princess Margaret Hospital, China
2Department of Orthopedic Surgery and Spine and Spinal Cord Center, Steel Memorial Muroran Hospital, Japan
3Department of Radiology, Steel Memorial Muroran Hospital, Japan
4Department of Radiology, Sapporo Medical University Hospital, Japan
5Department of Orthopedic Surgery, Hokkaido University Graduate School of Medicine, Japan
#Both authors contributed equally
*Corresponding author: Chong Hing Wong, Department of Orthopedics and Traumatology, Princess Margaret Hospital, Postal/Zip Code: 999077, 2-10 Princess Margaret Hosptial Road, Lai Chi Kok, Hong Kong SAR, China
Published: 13 Jul 2017
Cite this article as:
Abstract
Objective: To evaluate the radiation exposures (RE) to patient and surgeon during minimally
invasive lumbar spine surgery with instrumentation under the use of C-arm image intensifier or
O-arm intraoperative CT.
Background: Minimally invasive spinal instrumentation is highly dependent on intraoperative
imaging because of limited exposure of anatomic landmarks. The choice of imaging tools is
important not only for accuracy but also safety. Recently introduced O-arm with navigation is a
promising tool that could help to solve many problems encountered with C-arm, but the possible
increase in RE is a concern.
Materials and Methods: Twenty-five patients were included in this study; 11 patients who received
C-arm assisted surgery (8 PLF, 3 TLIF) and 14 patients who received O-arm assisted lumbar
fusion surgery (9 PLF, 5 TLIF). Patients were further divided into three subgroups: TLIF using
bilateral mini-Wiltse approach, midline approach TLIF, and midline approach PLF. Surgeon RE
was evaluated using a personal finger dosimeter. Patient's exposure was evaluated by an internal
dose registration systems of C-arm or O-arm devices respectively and converted into effective dose
(ED) using the established tissue weighting factors (WF). The O-arm (CT mode) ED was calculated
as Dose Length Product (DLP) x conversion index. The DLP=Computed Tomography Dose Index
weighted (CTDIw) x irradiated area (cm2). C-arm ED was calculated as Skin Surface Dose (SSD)
(mGy) × WF sum.
Results: The overall mean surgeon RE was 2.19 mSv in C-arm group and 0 mSv in O-arm
group (p=0.0003) and the overall mean patient ED was 41.85 mSv in C-arm group and 16.09 in
O-arm group (p=0.0004). The value was also lower in each O-arm subgroups when compared to
corresponding C-arm subgroups.
Conclusion: We introduced O-arm at our facility to allow the use of precise navigation during
surgery. Despite 2 or more CT acquisitions per surgery, the surgeon's RE was completely avoided
and patient's RE was reduced to less than a half that of C-arm's, which proves that O-arm is beneficial
for both surgeon and patients in MIS lumbar fusion surgery.
Keywords: Radiation exposure; C-arm; O-arm; Minimally invasive spinal instrumentation
Introduction
Minimally invasive posterior lumbar spine surgery is gaining its popularity. This modification
in access strategy minimizes the collateral soft tissue injury. Besides smaller incision and narrower
surgical corridor, it also avoids muscle denervation by using known neurovascular and muscular
compartment planes. Tendon attachments of paraspinal muscle are also preserved which is
important for the dynamic stability of spine [1]. Moreover, reduction of bone and ligament resection also preserved normal spine motion [2]. Because of less soft tissue
injury, this results in less post-operative pain, shorter hospital stay,
early recovery and may also lead to better long term result. However,
anatomical landmarks cannot be fully identified most of the time
because of the limited exposure, so intraoperative imaging becomes
indispensable for accurate instrumentation.
We have used C-arm as the imaging tool for our surgery but we
encountered problems including insufficient quality imaging, only
one projection at a time, instrument or other equipment may obscure
the view, risk of ‘hand on’ image which increases the radiation
exposure to surgeon’s hand and the need to manipulate the C-arm to
adjust the angle of projection which is labor consuming. Because of
repeated manipulation of the C-arm, it may contaminate the sterile
surgical field.
Introduction of the computer assisted surgery (CAS) navigation
system with O-arm solved these problems. Besides, it is also useful in
revision cases such as complex three-dimensional spine deformities
and fused spine in which the bony landmarks cannot be reliably
identified. On the other hand, the RE to surgeon and patient remains
a concern. In case of exposure the CT mode of O-arm could subject
the surgeon and patient to a higher dose of radiation than single
snapshot of C-Arm. To clarify this issue, we compared the radiation
exposure to the surgeon and patients while using C-arm and O-arm
with navigation system for minimally invasive spinal fusion surgery.
Materials and Methods
25 patients (11 males and 14 females) who underwent single or
double segment MIS lumbar fusion through a posterior approach
were prospectively enrolled in this study. The pathology included
degenerative spondylolisthesis in 16 cases, isthmic spondylolisthesis
in 5, recurrent disc herniation, degenerative lumbar spinal stenosis,
post-infective spondylitis instability and spondylolysis in one each.
The degrees of spondylolisthesis were limited to Myerding grade of
1 or 2. No major spinal deformity case was included in this study.
The spinal levels included were within L3 to S1. Only the recurrent
disc herniation case had a history of previous spine surgery. 11
patients had the operation done using C-arm (GE Health OEC 9900
Elite, Fairfield USA) and 14 patients underwent an operation using
O-arm® Surgical Imaging with Stealth Station® Navigation System
(Medtrontic, Minneapolis USA) using its standard mode. BMIs of
the patients were recorded. Each group was further divided into 3
subgroups: transforminal lumbar inter body fusion (TLIF) through
a bilateral Wiltse approach, TLIF through a midline approach
and posterior lumbar fusion (PLF) through a midline approach to
account for the heterogeneity within each group. All surgeries were
performed by the single surgeon (YK).
We use the fluoroscopy mode of O-arm to locate the level to
be navigated and then obtained 3D images using its CT mode. One
CT scan was enough to include the whole region of interest in all
cases. Further X-rays may be taken intra-operatively especially while
inserting the cage during TLIF for better positioning of the cage. After
completion of the instrumentation, another CT scan was obtained for
assessment of implant placement. If any adjustments had to be made,
another CT scan would be obtained for final confirmation.
The RE to surgeon was registered by a personal finger dosimeter.
The reading of the internal dose registration systems of C-arm and
O-arm devices were obtained and then converted into effective dose
(ED) received by a patient through the following equations:
For the C-arm and O-arm as a 2D fluoroscopy scanning, ED
(mSv)=Skin Surface Doses (SSG) (mGy) × Tissue Weighting Factors’
sum.
For the O-arm (CT mode) ED (mSv)=Dose Length Product
(DLP) x Conversion Index.
Conversion index for adult trunk is 0.015 as reported in literature
[3].
DLP=CT Dose index weighted (CTDIw) × radiation area
Total ED to patient in O-arm group was thus=ED (CT mode) +
ED (2D fluoroscopy scanning)
The Tissue Weighting Factors recommended by the International
Commission on Radiological Protection 2007 [4] were utilized.
The age, BMI, blood loss, operation time, one week post-operative
CRP, ED to patients and radiation dose to surgeon were compared
by using unpaired t-test with p value set at < 0.05 to consider as
statistically significant.
Results
The C-arm and O-arm cohorts were matched for age (64.45 ±
19.47 years vs. 65.36 ± 17.71 years in O arm and C arm respectively)
and the BMI (25.23 ± 3.37 kg/m2 vs. 25.10 ± 3.18 kg/m2 in O-arm
and C-arm respectively). There were two asymptomatic screw
misplacements in C-arm group and no screw misplacements or
complications in O-arm group.
The mean operation time was identical in both groups (133 min in
C-arm and 144 min in O-arm group) while the mean intraoperative
bleeding was significantly smaller in O-arm group (123 ml vs. 241
ml in C-arm group, p=0.005). The mean CRP values at one week
postoperatively were two times higher in the C-arm group (1.4 in
O-arm vs. 2.8 in C-arm group, p=0.1) (Table 1).
Mean exposition time was significantly longer in the C-arm
group (9.5 min vs. 0.57 min, p=0.0005).Mean surgeon RE was 2.19 ±
1.36 mSv in C-arm group and undetectable (0 mSv) in O-arm group
(p=0.0003) (Table 2). This was because the personnel can wait outside
the operation room to avoid RE during the acquisition of CT images.
In the subgroup of PLF, RE in C-arm was significantly higher than
that in o-arm (1.46 ± 0.64 vs. 0). The surgery was performed using
navigation without any further RE.
Using O-arm with navigation system led to a reduction of the ED
to the patient by half compared to C-arm group (Table 3). The mean
patient ED was 41.85 ± 16.86 mSv and 16.09 ± 10.5 mSv in C-arm and
O-arm groups respectively (p=0.0004). The mean EDs to a patient
were also significantly less in O-arm subgroup of PLF compared to
C-arm (37.4 ± 9.73 vs. 12.03 ± 8.30). Because of limited number of
cases, the t-test could not be performed for the TLIF subgroups but
the mean ED sin O-arm groups were much less than in corresponding
C-arm groups (41.79 vs. 25.60 ± 11.11 mSv and 59.59 ± 37.31 mSv
vs. 14.59 mSv in the bilateral Wiltse approach TLIF and posterior
approach TLIF respectively).
Discussion
The MIS spinal fusion surgery keeps increasing in popularity
because of its obvious benefits. This means that more and more
patients will undergo this highly imaging dependent surgery. Risk of
cumulative RE to both surgeons and patients is a growing concern.The complications of RE not only include the acute or deterministic
effects but also the late or stochastic consequence. The deterministic
effects such as skin erythema, tissue necrosis occur at the radiation
levels never encountered in spinal surgery [4-6]. The stochastic effects
mainly involve long term effect of carcinogenesis and hereditary
disease after low dose radiation exposure which can manifest 10-20
years later. The probability of combined stochastic effect is around
5% Sv-1 which should not be neglected in our daily practice (Table 4).
This is especially true in the era of wide utilization of imaging.
From 1980 to 2005, there was a 20 times increase in CT scanning in
United States [7]. The cumulative radiation exposure to patient from
surgery and also pre-operative and post-operative imaging can be
up to several times of the background radiation for years [8]. Spine
surgeons should be aware that the radiation dose for spine X-ray
is commonly higher than for other areas and it is highest for the
lateral lumbar spine X-ray [9]. Same is true concerning CT. CT of
axial skeleton is associated with substantial increase in RE and it is
highest for lumbar spine CT [10]. Therefore, choosing the imaging
tool and technique is important in order to satisfy the rule of ‘As Low
as Reasonably Achievable (ALARA)’ radiation exposure.
Fluoroscopy (C-arm) is the most traditional way for image
guidance. In non-instrumented surgery such as microdiscectomy,
Michael et al. [11] found that the surgeon is exposed to more
radiation in MIS lumbar microdiscectomy than open herniotomy.
This was due to extra fluoroscopy needed for tubular retractor
placement and adjustment. Moreover, Rampersaud also found that
fluoroscopically guided thoracolumbar pedicle screw insertion can
expose the surgeon to 10 to 12 times the RE of other non-spinal
musculoskeletal procedures [12]. The radiation exposure was still
within acceptable range in some surgeries such as TLIF or lateral
lumbar interbody fusion but it can be up to unacceptable levels in
others such as adolescent idiopathic scoliosis instrumentation [13-
15].
Computer assisted surgery (CAS) is becoming another choice
of intraoperative imaging and it provides intra-operative 2D or 3D
navigation. Nakagawa et al. [16] used fluoroscopic based 2D image
computer assisted surgery (virtual fluoroscopy) for the insertion
of pedicle screws on a plastic model. He found the accuracy of the
navigation system was satisfactory and he expected reduction in
radiation exposure by using this system. Further studies also showed
that CAS can reduce the chance of malposition of pedicle screws in
scoliosis surgery and cervical pedicle screw surgery [17,18]. Those
cases are technically demanding because of small pedicle size and
distorted anatomy.
Besides the high accuracy and avoidance of the aforementioned
drawbacks of fluoroscopy, RE remains a concern in CAS.
Slomczykowski et al. [19] found that using CAS based on preoperative
CT for pedicle screw insertion requires a higher RE than
intraoperative fluoroscopy. He suggested that optimizing the CT
protocol to reduce the RE and the advantages of CAS justify the
radiation when indicated.
Use of navigation-assisted fluoroscopy is able to reduce the
radiation dose but it only provides 2D images [20]. The Iso-C, a CT
based CAS with intra-operative 3D image acquisition was developed
and it was proven to reduce the radiation exposure to both surgeon
and patient in balloon kyphoplasty and pedicle screw insertion
[21,22]. O-arm with navigation system also serves the same purpose
but its radiation dose had to be justified. Research found that radiation
received by patients of the standard CT mode of O-arm is less than
that of a standard abdominal CT scan [23]. The radiation to surgical
team was minimal and far below the occupational exposure limit as
they can wait in sub-sterile area during imaging [24]. However Parks
et al. [25] found that the surgeon received more radiation while using
fluoroscopy mode of O-arm than C-arm. Therefore, evaluation of the
total radiation dose and comparison with other radiological tools is
needed.
In our study, O-arm with navigation system exposed the surgeon
to minimal radiation as they went to the sub-sterile area during
image acquisition. Also the exposition time was significantly longer
in C-arm group producing much higher RE to the patient. The same
results were also demonstrated by other authors. We also found that
the ED to patient was no more than a half of C-arm’s. This means that
O-arm is a safer option for image guidance in view of high accuracy
and lowers RE. Besides, as CT mode of O-arm can provide navigation
for several levels after one image acquisition session, this advantage
will grow in multilevel surgery. Moreover, screw misplacement
is picked up on the intraoperative CT and corrected immediately
obviating the need for revision surgery.
Tabaree et al. [26] conducted a cadaveric study that showed
different findings. It is difficult to compare their results with ours
because of different measurement methods for radiation exposure,
different study subjects (in vivo vs. cadaveric) and also different
imaging protocol. The high resolution mode of O-arm will subject
the patient to higher radiation dose than standard protocol that we
used. Simply difference in the position of the imaging machine can
also increase the radiation dose up to 3 times [27]. Besides, the result
of the study should be interpreted with caution as it showed the
radiation exposure to surgeon’s hand and thyroid was undetectable
after insertion of 12 thoracic pedicle screws under C-arm guidance.
Surgeon’s hand is supposed to be the closest to the radiation source
but it appeared to receive the least radiation dose. Moreover, in
the MIS group, although they were working on the lumbar spine,
the radiation exposure to the sternum was even higher than that to
anterior abdomen. Similar situation happened in the O-arm group
in which the radiation to the anterior abdomen is higher than that of
sternum while performing thoracic pedicle screw insertion. Erik Van
et al. [28] using a database of more than a thousand pedicle screws
places with the help of O-arm navigation found that if the surgeon is
confident of the screw position, the risk of malposition of screw on CT
is only 1%. In their opinion this means that an intraoperative CT scan
after the screw placement to search for misplacements might not be
necessary. However, we strongly believe that finding out a misplaced
screw and correcting the error without the need for a reoperation in
at least 1 out of every 25 surgeries is well worth taking routine post
instrumentation intraoperative CTs.
The limitations of this study are limited cohort, indirect
measurements of the patients’ RE and the fact that the CDTI used
for our calculations is based on results obtained from a standard
phantom rather than real human body. Further development of
technologies for accurate ED measurement might be needed.
Table 1
Table 2
Table 3
Table 4
Table 4
Detriment-adjusted nominal risk coefficients for stochastic effects after exposure to radiation at low dose rate (10-2 Sv-1).
Conclusion
Although we introduced O-arm at our facility to allow the use of precise navigation during surgery, we anticipated an increase in RE. However, notwithstanding 2 or more CT acquisitions per surgery the surgeon’s RE was completely avoided and patient’s RE was reduced to less than a half that of C-arm’s, which proves that O-arm is beneficial for both surgeon and patient in MIS lumbar fusion surgery. Although O-arm assisted surgery requires additional time for reference frame placement, instrument registration and bony landmark verification, the mean operation time was statistically identical in O-arm and C-arm groups in our study which means that actual instrumentation time got shorter in O-arm group.
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