Key words kyphoplasty - radiation safety - technical aspects - spine
Introduction
The use of minimally invasive surgical techniques under fluoroscopy guidance in orthopedics
and trauma surgery has become increasingly important in recent years. In particular,
the transpedicular treatment of vertebral body fractures with dorsal stabilization
and/or kyphoplasty are examples of radiation exposure of staff and surgeons [1 ].
The goal of this study was to determine the surgeon's radiation exposure in the treatment
of osteoporotic vertebral body fractures via kyphoplasty using two different kyphoplasty
systems. Balloon kyphoplasty is currently the most commonly used minimally invasive
method. Radiofrequency kyphoplasty represents an alternative method which promises
to be less invasive and to lower the surgeon's radiation exposure [2 ].
As the age profile of the population in industrialized countries changes, the probability
of a symptomatic vertebral body compression fracture increases. Affected patients
have a lower quality of life as a result of limited mobility. This is associated with
an increasing number of cardiovascular diseases and thus an increase in mortality
of approximately 23 % compared to the unaffected control group [3 ]
[4 ]
[5 ]
[6 ]. Minimally invasive vertebral body stabilization procedures using cement to stabilize
the vertebral body and reduce patient pain as quickly as possible were developed to
accelerate the mobilization of patients often with multimorbidity.
In a preliminary study as part of the EU project ORAMED (Optimization of Radiation
Protection of Medical Staff), a Belgian working group was able to show a dose reduction
for the surgeon in bipedicular kyphoplasty procedures with and without use of a cement
application system (CDS) [7 ]. Therefore, the radiation exposure was able to be reduced by approximately 70 %
for the left hand and by 20 % for the eye lens. The personal dose (Hp 0.07) was determined
at defined locations.
The personal dose (Hp 0.07) corresponds to the equivalent dose at a depth of 0.07 mm
at the location where the personal dosimeter is worn. It is measured by partial-body
dosimeters (e. g. ring dosimeter). It provides an estimate for the local skin dose
and the lens dose.
The equivalent dose H cannot be directly measured but rather corresponds to the biological
effect in connection with the absorbed dose. The effect of the radiation on biological
tissue with the same absorbed dose depends on the type of radiation.
Materials and Methods
A balloon kyphoplasty system (Medtronic GmbH) and a radiofrequency kyphoplasty system
(StabiliT, DFine Europe GmbH) were used in this comparative study.
Balloon kyphoplasty typically requires bipedicular access to the vertebral body. The
puncture cannula must be replaced by a working cannula via a K-wire. The working cannula
is then used to perform the procedure to restore the height of the vertebral body
with balloons. The cavities in the vertebral body are then filled with cement that
ideally interlocks with the adjacent spongiosa. In balloon kyphoplasty, cement applicators
are inserted bilaterally via the working cannulas. Cement is applied manually within
the fluoroscopy field. The CDS allows the cement to be applied from outside the fluoroscopy
field. The length of the application tube is maximal 120 cm and the cement is applied
manually by means of water hydraulics.
Radiofrequency kyphoplasty requires only a single unipedicular access to the vertebral
body since use of a special flexible osteotome in the center of the vertebral body
ensures that the cement is distributed in the vertebral body. The puncture cannula
also functions as the working cannula and does not need to be replaced. A control
unit is used to apply the cement via water hydraulics. The cement application can
be controlled at a distance of up to 3.0 m from the fluoroscopy field by means of
an operating element. The cement is activated by a special activation element on the
application needle just prior to insertion into the vertebral body.
40 patients with a fracture in the thoracolumbar junction or in the lumbar spine were
randomly treated with one of the kyphoplasty systems ([Table 1 ]). The average age of the patients in the balloon kyphoplasty group was 76.9 years
(min. 57 years, max. 95 years) and the ratio of men to women was 9 to 11. The average
age of the patients in the radiofrequency kyphoplasty group was 75 years (min. 54
years, max. 89 years) and the ratio of men to women was 7 to 13.
Table 1
Treated vertebral bodies.
balloon kyphoplasty
radiofrequency kyphoplasty
Th11
0
1
Th12
5
7
L1
7
5
L2
4
5
L3
2
1
L4
2
1
total
20
20
The size and weight of each patient were registered and used to determine BMI. The
average BMI was 27.6 (min. 26.2, max. 38.8) for the balloon kyphoplasty patient group
and 29.3 (min. 24, max. 40.6) for the radiofrequency kyphoplasty group.
Both systems were already in use at the hospital prior to the study (starting in 2011).
In the period from April 2013 to February 2014, osteoporotic vertebral body fractures
were treated under local anesthesia on a monoplanar angiography system (Siemens Artis
zee). The interventions were performed by the same surgeon with many years of experience
in both balloon kyphoplasty and radiofrequency kyphoplasty. The angiography system
is equipped on-site with undertable radiation protection strips, overtable lead strips,
and a mobile lead glass screen. The footswitch for triggering radiation is connected
to the system via WLAN so that triggering can be performed at any distance from the
fluoroscopy field. AP and lateral projections were used. In the AP projection the
X-ray tube was tilted maximal 15° in the cranial or caudal direction. The X-ray tube
was positioned under the table for the AP projection and to the right of the patient
for the lateral projection.
Prior to every examination, TLD chips (thermoluminescence detector) were attached
at defined locations to determine the surface dose. TLD chips were attached to the
forehead between the eyes (lens dose), to the inner surface of the left and right
wrist, to the X-ray apron at the level of the costal arch, and to the left ankle.
The left ankle was facing the fluoroscopy field, i. e., the left half of the examiner's
body was the side near the tube.
The distances from the fluoroscopy field were marked on the floor for each procedure
(balloon kyphoplasty 1.20 m and radiofrequency kyphoplasty 2.40 m) to clearly define
the distances as determined by the room size.
The dose area product for the entire procedure was determined and recorded
The TLD chips were evaluated as quickly as possible at the Landesanstalt für Personendosimetrie
und Strahlenbelastung Berlin (LPS Berlin). The background radiation (measuring point)
was 0.009 +/– 0.004 mSv. The decision threshold was 0.02 mSv and the detection limit
was 0,03 mSv. The confidence level of the measurement uncertainty was +/– 95 % (k = 2).
3 work steps were defined in order to be able to compare the working times and fluoroscopy
times for each application.
Work step 1 was the planning and setting of the projections for the intervention.
The examiner stands to the left of the patient with the left body side facing the
X-ray tube. The lead glass screen can be used.
In radiofrequency kyphoplasty, work step 2 included the unipedicular vertebral body
puncture under fluoroscopy and the application of the osteotome. The examiner again
stands to the left of the patient. It is not possible to use the lead glass screen
during puncture of the vertebral body and the examiner’s hand must be in the fluoroscopy
field during fluoroscopy in order to ensure correct determination of the puncture
angle and correct positioning with respect to the vertebral arch. For balloon kyphoplasty,
this work step included bipedicular puncture of both vertebral arches, replacement
of the working cannulas, and bilateral application of the balloons under fluoroscopy.
Also in this case the examiner stands to the left of the patient table and the examiner’s
hands are partially in or very close to the fluoroscopy field.
The last and 3rd work step for both systems was cement application and final imaging on 2 planes.
In this work step the examiner was able to be 1.20 m from the fluoroscopy field for
balloon kyphoplasty and 2.40 m for radiofrequency kyphoplasty when using a CDS.
Results
On average, the patients in the balloon kyphoplasty group were 2 years older, while
the group of radiofrequency kyphoplasty patients included a higher percentage of women.
With respect to BMI, the patients in both groups were overweight on average. Both
groups included 3 patients in obesity class I. 3 patients in the balloon kyphoplasty
group and 2 patients in the radiofrequency kyphoplasty group were in obesity class
II and 1 patient in the radiofrequency kyphoplasty group was in obesity class III.
The fluoroscopy times for the individual work steps are shown in [Table 2 ].
Table 2
Average working times and fluoroscopy times for the individual work steps in balloon
and radiofrequency kyphoplasty in minutes.
planning
puncture
cement
planning
puncture
cement
time in minutes
fluoroscopy time in minutes
balloon kyphoplasty
2.4
19.3
8.9
0.75
4.3
2.1
radiofrequency kyphoplasty
2.4
7.9
8.4
0.63
1.3
0.82
There were no significant differences with respect to working time and fluoroscopy
time in work step 1. Both the working time and the fluoroscopy time were higher by
a factor of 2 to 3 in work step 2 for the patients in the balloon kyphoplasty group. Work
step 3 included a longer fluoroscopy time for the patients in the balloon kyphoplasty
group.
The average dose area product was 2352,1 µGym² (min. 820.5 µGym², max. 4844.3 µGym²)
for balloon kyphoplasty and 925.9 µGym² (min. 100.6 µGym², max. 1570.8 µGym²) for
radiofrequency kyphoplasty.
The average total fluoroscopy time for all work steps was 07:32 minutes for balloon
kyphoplasty and 02:31 minutes for radiofrequency kyphoplasty.
The average personal dose values are shown in [Table 3 ].
Table 3
Mean personal dose values in mSv for balloon kyphoplasty and radiofrequency kyphoplasty.
dose in mSv
forehead
on the X-ray apron
right wrist
left wrist
left ankle
balloon kyphoplasty
0.217
0.67
1.249
3.908
0.154
radiofrequency kyphoplasty
0.05
0.137
0.198
0.523
0.06
Discussion
Considering the BMI in both kyphoplasty groups, a higher radiation dose for the surgeon
is to be expected when performing radiofrequency kyphoplasty based on the higher BMI
values in the radiofrequency kyphoplasty group. The patient with the highest BMI of
40.6 was in the radiofrequency kyphoplasty group and also had the highest dose area
product value in this group (1570.8 µGym²) as expected. However, the highest individual
(4844.3 µGym²) and total (2352.1 µGym²) dose area product values for all work steps
were in the balloon kyphoplasty group. As the BMI values show, this was not due to
patient characteristics but rather primarily to the longer fluoroscopy times needed
for balloon kyphoplasty especially in work step 2 with the bipedicular access and
the replacement of the puncture cannula with the working cannula. The total fluoroscopy
time for all work steps was three times longer in balloon kyphoplasty and this is
reflected in the dose area product which was twice as high on average.
For the surface dose and lens dose ([Fig. 1 ], [2 ]), the greatest differences were seen with respect to the wrists and especially the
left wrist. Since the TLDs have a lower detection limit of 0.03 mSv and the dose values
for radiofrequency kyphoplasty are close to 0 mSv, the measured values were 0 for
the lens in two cases and 0 for the right wrist in one case. These values were used
in the statistical analysis even though they correspond to a systematic error.
Fig. 1 Box plot of the dose values measured on the forehead during balloon and radiofrequency
kyphoplasty.
Fig. 2 Box plot – comparison of the measured dose values for both wrists during balloon
and radiofrequency kyphoplasty systems.
The reason for the higher dose values for the left wrist is the position of the surgeon
to the left of the patient so that the left side of the surgeon's body was facing
the direct radiation field. On average, the measured surface doses for the lenses
were four times higher in balloon kyphoplasty. The values for the left wrist were
almost 8 times higher in balloon kyphoplasty. Although the effect of the greater distance
from the radiation source during cement application in radiofrequency kyphoplasty
is positive, the relevant dose difference is the result of the unipedicular access
in work step 2.
The hypothesis that a unipedicular procedure has clear dose advantages for the surgeon
compared to a bipedicular procedure was able to be confirmed in this study. This method-based
difference had not yet been proven in this manner in earlier studies. Numerous studies
have addressed dose reduction methods using various cement application techniques
or the advantage of using radiation protection equipment during puncture and cement
application in the direct radiation field [8 ]
[9 ]
[10 ]. The determination of the local dose for individuals participating in surgery has
also been the objective of studies [11 ]
[12 ]. The comparison of various kyphoplasty systems under consideration of radiation
dose for the surgeon is new and has not yet been examined in any studies. Ultimately,
reducing the surface dose by reducing the time spent in the direct radiation field
is the more effective means of radiation protection that must be further optimized
by the use of radiation protection equipment. The inverse square law can be better
applied in the case of cement application using water hydraulics in radiofrequency
kyphoplasty.
A stationary X-ray system equipped on-site with the corresponding technical radiation
protection equipment that is usually not present for procedures in the operating room
with mobile systems (C-arm) was used in this study. Therefore, additional studies
using mobile X-ray systems should be performed to obtain reliable values for the real
radiation dose for the surgeon in the operating room.
If the results from the ORAMED study are included, use of balloon kyphoplasty without
CDS and radiation protection equipment can no longer be accepted with respect to a
reduction of the surface dose particularly for the left hand and the eyes. The surface
dose values must also be measured by ring dosimeters and dosimeters on the radiation
safety goggles, particularly in light of the lowering of the annual limit for the
eye lenses from 150 mSv to 20 mSv in the new X-ray Ordinance dated 1/1/2019.
Conclusion
Use of a unipedicular kyphoplasty system must be recommended for radiation hygiene
purposes. If balloon kyphoplasty is used for medical reasons, all radiation protection
equipment (lead gloves, lead glass screen, and radiation protection goggles) are to
be used and the surface dose for both hands must be recorded and documented by a ring
dosimeter and the lens dose by a TLD on the radiation protection goggles. It is no
longer acceptable to use balloon kyphoplasty without a CDS.
