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374
The Neuroradiology Journal 21: 374-382, 2008 www. centauro. it
Radiation Dose Optimization in CT Planning
of Corrective Scoliosis Surgery.
A Phantom Study
K. ABUL-KASIM*, M. GUNNARSSON**, P. MALY*, A. OHLIN***, P. SUNDGREN****
* Department of Radiology, Section of Neuroradiology; ** Department of Radiation Physics; ***Department of Orthopedic Surgery,
University of Lund, Malmö University Hospital; Sweden
**** Department of Radiology, University of Michigan Health System; Ann Arbor USA.
Key words: scoliosis, low dose helical CT, effective dose, dose reduction system (DRS)
Introduction
Adolescent idiopathic scoliosis (AIS) most
often affects adolescent girls. The prevalence
of AIS exceeding a Cobb angle of 20 degrees is
estimated to be in the range of 0.2 % 1. These
patients are usually examined initially with
lateral and posteroanterior (PA) radiograph.
Subsequently the Cobb angle is measured on a
single PA radiograph.
The continuous development and improve-
ment of the corrective methods and implemen-
tation of new implants make it necessary to
obtain a detailed anatomical map of an often
large region of interest both before and after
corrective spinal surgery. Preoperatively the
surgeon needs a precise estimation of the de-
gree of vertebral rotation in order to plan the
correct insertion of transpedicular screws at
different levels. Furthermore he/she needs in-
formation about the width as well as length of
the pedicles, not seldom of up to 15 vertebral
levels, in order to plan the suitable diameter of
screws at various vertebral levels. As such in-
SUMMARY – The aim of the study was to explore the possibility of obtaining a helical CT scan of
a long segment of vertebral column, optimally reduce the radiation dose, compare the radiation dose
of the low dose helical CT with that of some of the CT protocols used in clinical practice and finally
assess the impact of such a dose reduction on the image quality. A chest phantom was examined
with a 16-slice CT scanner. Six scans were performed with different radiation doses. The lowest
radiation dose which had no impact on image quality with regard to the information required for
surgical planning of patients with scoliosis, was 20 times lower than that of routinely used protocol
for CT examination of the spine in children (0.38 mSv vs 7.76 mSv). Patients with scoliosis planned
for corrective spinal surgery can be examined with low dose helical CT scan. The dose reduction
systems (DRS) available in modern CT scanners contribute to dose reduction and should be used.
formation cannot be obtained from plain radio-
graph 2
; a CT examination of a large segment
of the vertebral column is required. Performing
such a CT examination of spine, according to
CT protocols available in daily clinical practice
that are aimed for morphological evaluation of
the spine and investigation of different spinal
pathology means exposing these young individ-
uals to high radiation dose.
The present availability of multislice scan-
ners and the possibility of reducing and indi-
vidually adjusting the radiation dose by us-
ing the manufacturer’s dose reduction system
(DRS) (CareDose 4D, Siemens AG, Forchheim,
Germany) have enabled us to tailor a very low
radiation dose protocol which provides 3D in-
formation of relevant segments of the thoracic
and lumbar spine. This tube current modula-
tion system includes both angular modulation
and z-axis modulation 3
with the aim to auto-
matically adapt the tube current to the patient’s
anatomic configuration and size together with
an on-line controlled tube current modulation
for each tube rotation 4. The major aim of this
K. Abul-Kasim Radiation Dose Optimization in CT Planning of Corrective Scoliosis Surgery
375
phantom study was to compare the radiation
dose of the here proposed low dose 3D helical
CT protocol with that of some of the CT proto-
cols that are routinely used in clinical practice,
before implementing this low dose CT protocol
in clinical routine.
The other aims of this phantom study were
to assess the impact of this optimal dose reduc-
tion on image quality and to find the dose level
that still allows safe and reliable assessment of
the required parameters such as measurement
of pedicular width.
Materials and Methods
The anthropomorphic adult chest phantom
(PBU-X-21; Kyoto Kagaku CO, Ltd, Kyoto, Ja-
pan) was used in this study (figure 1). It con-
tains substitute materials for human soft tis-
sues such as muscles and blood vessels. Bones
are simulated by epoxy resins and calcium
hydroxyapatite to achieve changes in contrast
in the phantom images as in an actual human
body.
The examinations were performed on a 16-
slice CT scanner (SOMATOM Sensation 16,
Siemens AG, Forchheim, Germany).
Following scout view, the phantom was ex-
amined with the following scans (table 1 shows
scan parameters of every individual scan):
Scan 1: CT spine protocol recommended by
the manufacturer for investigation of different
spinal pathology in adults 5.
Scan 2: CT spine protocol recommended by
the manufacturer for investigation of differ-
ent spinal pathology in children with fixed
tube voltage of 120 Kv and tube current-time
product depending on the body weight. In this
study the tube current-time product was 140
mAs (130 mAs recommended by manufacturer
for patients with body weight of 35-44 kg) 5.
Scan 3: “Apical Neutral Vertebra” CT proto-
col (ANV-protocol). This protocol had been used
in our institution to measure the degree of ver-
tebral rotation prior to the planned corrective
surgery and to measure the degree and derota-
tion after surgery. It consists of four sequen-
tial slices of the apical vertebra (at the scoliotic
apex), at the superior and the inferior end ver-
tebra at either end of scoliotic curvature.
Scan 4: The low dose 3D helical CT protocol
before applying the DRS.
Scan 5: The low dose 3D helical CT protocol
taking advantage the DRS (the here proposed
low dose CT protocol).
Scan 6: 3D helical CT protocol with the low-
est possible radiation dose in our CT system.
For all helical scans, i.e. except scan number
3, the scan length was 36.5 cm. The number
of vertebrae included in these scans was 15.
Reconstructed slice thickness was 3 mm with
increment of 3 mm. Scan number 2 (ANV-pro-
tocol) consisted of four sequential slices at the
middle of each of the three vertebral bodies im-
aged (only 1.2 cm of each of the three vertebral
bodies has been scanned.
The signal-to-noise ratio (SNR) expressed
as the ratio of the mean pixel value (MPV) to
the standard deviation (SD) of the pixel values,
was estimated at the same level of the verte-
bral column (L1) for every single scan, using a
one cm large region of interest (ROI).
A subjective evaluation of image quality was
performed by two readers. All scans were read
independently by two senior radiologists who
were blinded to scan parameters with the aim
of evaluating: (a) the ability of the scan to vis-
ualize the vertebral pedicles at different seg-
ments of the vertebral column and (b) the pos-
sibility of measuring the width of the pedicles.
The readers were asked to grade the degree of
evaluation reliability in every single scan as:
(A) unreliable, (B) relatively reliable or (C) reli-
able.
For quantitative evaluation of the impact of
dose reduction on image quality, 3 mm thick
reformatted images from scan 1 (the highest
radiation dose tested), from scan 5 (the here
proposed low-dose CT protocol) and from scan
6 (the lowest possible radiation dose in our CT
system) were blinded to all information related
to scan parameters and sent to the Picture Ar-
chiving and Communication System (PACS,
Agfa IMPAX). Since there was no vertebral ro-
tation in the study phantom, the quantitative
evaluation of the impact of dose reduction on
image quality was limited to the measurement
of the pedicular width. Two independent ob-
servers performed measurements of pedicular
width of 28 pedicles in every scan (a total of
84 pedicular width measurements per observer
and occasion). The same measurements were
performed by one observer on two different oc-
casions with a one week interval.
Statistical analysis was performed in SPSS
15. Twenty four paired sample T-tests were
performed to explore the inter- and intraob-
server variations between measurements done
on scans 1, 5 and 6 as well as between measure-
ments done within the same scan by two differ-
ent observers and by the same observer at two
376
Radiation Dose Optimization in CT Planning of Corrective Scoliosis Surgery K. Abul-Kasim
different occasions. The level significance was
decided to be P≤0.01. The mean value for dif-
ferences in measurements of pedicular width
was expressed as the systematic error while
the standard deviation of the aforementioned
values was expressed as the random error.
MSCT Dosimetry
The effective mAs concept was introduced
with the (SOMATOM Sensation 16, Siemens
AG, Forchheim, Germany) MSCT. The effec-
tive mAs take into account the influence of
pitch on both the image quality and the radia-
tion dose and is defined as tube current-time
product/pitch factor 4. The effective mAs value
was recorded for scan 5 i.e. scan with activated
DRS (table 1).
E = EDLP .DLP (mSv)
Where EDLP is the region-specific, DLP nor-
malized effective dose (mSv/mGy.cm). General
values of the conversion factor, EDLP, appropri-
ate to different anatomical regions of the pa-
tient (head, neck, chest, abdomen, pelvis) were
taken from European commission 2004 CT
Quality Criteria, Appendix A-MSCT Dosimetry
6. This phantom study included the thoracic
and abdominal regions and the conversion fac-
tor used was 0.018 (average of 0.019 for the
chest and 0.017 for the abdomen).
The effective doses obtained from calculation
of the data from this phantom study were com-
pared with the effective doses which were cal-
culated by using Monte Carlo simulation pro-
gram WINDOSE 3.0 (Scanditronix Wellhöfer,
GmbH; Germany).
Table 1 Scan parameters of all scans in the phantom study. The values marked in bold represent the scan parameters of the
here proposed low dose CT protocol. Effective tube current-time product shown in column 6 is expressed as IQR mAs and effec-
tive mAs, respectively, in scan 5 taking advantage of DRS. (IQR mAs is the Image Quality Reference mAs). (*) Minor modifica-
tion from the manufacturer’s protocol (16x1.5 mm recommended by Siemens). The pitch is however the same as manufacturer’s
recommendation.
Slice
collimation, mm Rotation
time, sec Pitch Tube voltage,
Kv Effective tube current-time
product, effective mAs
Scan 1 16×0.75* 0.75 0.75 120 300
Scan 2 16×0.75* 0.75 0.75 120 140
Scan 3 12×1.50* 1.00 1.00 120 060
Scan 4 16×0.75*0.75 1.50080 025
Scan 5 16×0.75*0.75 1.50080 IQR mAs 25
Effective mAs 19
Scan 6 16×0.75*0.50 1.50080 017
Results
The results of measurements of CTDIvol, DLP
and the effective doses for scans 1 to 6 are
shown in table 2 (columns 2-5). The effective
doses of all scans are also shown in figure 2.
The effective dose (table 2, column 4) of the
here proposed low-dose 3D helical scan taking
advantage of the DRS (Scan 5) was 0.38 mSv
which is 44 times lower than that of scan 1
(16.6 mSv), 20 times lower than that of scan 2
The volume CTDI (CTDIvol) which is a deriv-
ative of the computed tomography dose index
(CTDI) and the dose length product (DLP) was
recorded for every scan included in this study.
To allow comparisons with other type of radio-
logical examinations, the effective dose (E) was
determined.
The effective dose may be derived from val-
ues of DLP for an examination using appropri-
ate conversion factors and the following equa-
tion:
www. centauro. it The Neuroradiology Journal 21: 374-382, 2008
377
(7.76 mSv) and 12% lower than that of the scan
3/ANV-protocol (0.43 mSv). The latter merely
provides few sequential images at only three
vertebral levels. Applying the DRS has low-
ered the effective dose by 19% (from 0.47 mSv
in scan 4 to 0.38 mSv in scan 5).
According to the Monte Carlo calculation (ta-
ble 2, column 5) the effective dose of the here
proposed low dose CT protocol of the spine
(scan 5) was 0.34 mSv which is 55 times lower
than that delivered by scan 1 (18.6 mSv), 25
times lower than that delivered by scan 2 (8.6
mSv) and 30% lower than that of the ANV-pro-
tocol (0.49 mSv).
The calculated absorbed dose to the breasts
and the genital organs are shown in table 2, col-
umns 6 and 7, respectively. In the CT protocol
recommended by the manufacturer for inves-
tigation of spinal disease in children (scan 2),
the absorbed dose to the breasts and the geni-
tal organs was 23 times and 32 times, respec-
tively, higher than that of the here proposed
Table 2 Results of all scans in the phantom study show the CTDIvol, DLP, mean effective dose, the absorbed dose to the breast
and the genital organs as well as image quality (SNR). (*) refers to the estimated effective dose, the absorbed doses to the breast
and to the genital organs according to Monte Carlo calculations WINDOSE 3.0. The values marked in bold represent the CTDI-
vol, DLP, effective dose and the lowest absorbed dose to the breasts and the genital organs in the here proposed low dose CT
protocol.
CTDIvol,
mGy
DLP
mGy.cm
Effective
dose, mSv
Effective
dose, mSv*
Absorbed dose
to the breasts,
mGy*
Absorbed dose
to the genital
organs, mGy*
SNR=
MPV/SD
Scan 1 23.40 920 16.60 18.6 33.301.900 167/500
Scan 2 10.92 431 07.76 08.6 15.500.900 168/380
Scan 3 4.32 3×8=24 00.43 0.1+ 0.19+
0.2=0.49 01.31 0.028 166/640
Scan 4 00.65 26 00.47 00.45 00.86 0.037 176/174
Scan 5 00.51 21 00.38 00.34 00.66 0.028 175/182
Scan 6 00.44 19 00.34 00.30 00.55 0.025 160/347
0
2
4
6
8
10
12
14
16
18
Scan 1 S can 2 S can 3 Scan 4 S can 5 Scan 6
Effective dose mAS
↑ Figure 2 The effective radiation dose for all scan settings
(scans 1-6).
← Figure 1 The adult phantom used in this study was con-
structed to contain about 15 vertebral bodies, ribs, two lungs,
trachea and soft tissue in the abdomen and in the thoracic
and abdominal walls.
378
Radiation Dose Optimization in CT Planning of Corrective Scoliosis Surgery K. Abul-Kasim
low-dose CT protocol (scan 5). In the ANV-pro-
tocol (scan 3) the absorbed dose to the breasts
was twice as high as the here proposed low-
dose CT protocol (scan 5) while the absorbed
dose to the genital organs was the same in both
scans (0.028 mSv).
The readers classified all images of scans 1 to
5 including those of the here proposed low dose
CT protocol (scan 5) as reliable with respect
to identification of the pedicles, and measur-
ing their width. The overall image quality of
scan 6 was classified as unreliable in the lower
five vertebral levels and relatively reliable in
the upper ten vertebral levels. Due to this dif-
ference in overall image quality of scan 6, the
statistical test (paired sample T-test) was also
performed separately for the lower five verte-
bral levels (i.e. 10 pedicles out of 28).
The results of the SNR (MPV/SD) calcula-
tions are shown in table 2, column 8. The fact
that the SNR value of the here proposed low
dose CT protocol (scan 5) was 35 times lower
than that of scan 1 (with the highest radia-
tion dose) does not seem to affect the reliability
of the evaluation of the parameters required.
Some examples of images from different scans
of this study are shown in figure 3A-D.
The quantitative evaluation of the impact of
dose reduction on image quality in scans 1, 5
and 6 is shown in table 3, which shows only the
statistically significant results of paired sample
T-tests. Five of the 24 performed paired sam-
ple T-tests resulted in statistically significant
differences in pedicular width measurements.
Scan 6 (with lowest possible dose in our CT
system) was involved in all five paired tests,
out of which three pairs involved differences
in pedicular width measurements in the lower
five vertebral levels.
Discussion
This study has shown that it would be possi-
ble to examine a large segment of the vertebral
column (15 vertebrae) with a long helical 3D
CT scan while exposing the patient to a mark-
edly lower radiation dose than would do the CT
scan performed according to protocols used in
daily clinical practice or the previously used CT
scan with sequential images over a very limited
part of the vertebral column according to the
ANV-protocol (table 2 and figure 2). The lat-
ter CT protocol merely enabled measurement
of the degree of vertebral rotation (preopera-
tively) and degree of vertebral derotation (post-
operatively) whereas the low-dose helical CT of
a considerably larger area of vertebral column
gives, in addition, the opportunity to study its
morphology. The fact that some pedicles at the
apex of the scoliotic curvature can be merely
2-3 mm wide and may have to be subsequently
excluded from transpedicular screw insertion
makes the reliability of the measurements of
pedicular width crucial in the preoperative
planning.
Scan 6 (scan with the lowest possible dose
in our CT system) is involved in all five paired
comparisons with statistically significant dif-
ferences in pedicular width measurements.
This result is compatible with the two reader’s
subjective classification of images of scan 6 as
relatively reliable and of those in the lower
five vertebral levels as unreliable. In these five
pairs involving scan 6, besides the statistical
significance of the differences, the inter- and
intraobserver random errors in measuring the
pedicular width varied between 1.1 mm and 1.6
mm while the systematic error varied between
1.2 mm and 2.4 mm. The magnitude of the dif-
ferences exceeding 1 mm also makes the results
significant from the clinical point of view as
they have a significant influence on the choice
of appropriate screw diameter. Unlike the com-
parisons involving scan 6, none of the compari-
sons between scan 5 and scan 1 with respect to
the inter- and intraobserver random error and
the systematic error in measuring the pedicu-
lar width resulted in significant differences
and were always less than 1 mm (not shown
in table 3 because these results were statisti-
cally non significant). Taking these statistical
findings into consideration, the parameters of
the here proposed low dose helical CT protocol
(table 1) are to be considered a cut-off value to
which the radiation dose can be reduced with
no significant impact on image quality required
for planning of scoliosis surgery.
In the beginning of 1990s CT constituted
about 2-3% of all radiological examinations 7
and contributed to about 20-30% of the total
radiation load from medical use of ionizing ra-
diation 8. Later reports increased the latter fig-
ure to about 50% 6,9.
In Germany an overview of MSCT examina-
tions conducted in 2001 showed that the aver-
age effective dose to patients had changed from
7.4 mSv at single-slice to 5.5 mSv and 8.1 mSv
at dual- and quad-slice scanners, respectively 10.
The annual per capita effective dose for the UK
in 2001-2002 was estimated to be 0.38 mSv 11
and for the Dutch population in 1998 to be 0.59
www. centauro. it The Neuroradiology Journal 21: 374-382, 2008
379
mSv 12. European Commission reference dose
levels (EC RDLs) were applied to the routine
CT examinations for a random sample of ten
patients in the Euromedica medical center in
Greece 13. The mean value of the effective dose
was 10.9 mSv for the chest and 7.1 mSv for the
abdomen. Both the CTDI vol and the effec-
tive dose of the abdomen CT met the EC RDLs
criteria 13. Also the CTDI vol of the scans of the
chest met the EC RDLs dose criteria but the
effective dose exceeded the recommended dose.
That has been explained by high DLP-value
(large irradiation volume length). According
to this protocol that had the purpose of apply-
ing the EC RDLs criteria, the total effective
dose was 18 mSv for the chest- and abdominal
scans, a region that corresponds to the region
examined in this study with the low dose heli-
Figure 3 A-D Examples of axial images obtained at the same level of the spine, using different protocols. A) Scan 1 according to
the protocol for CT-spine recommended by the manufacturer for investigation of different skeletal spinal pathology in children.
B) Scan 3 according to ANV-protocol. C) Scan 5 with the low radiation dose according to the here proposed low dose helical CT
protocol. D) Scan 6 with the lowest possible radiation dose in our CT system. Undoubtedly the best image quality is that of image
A but the detail in image C allows reliable measurement of the width of the pedicles. The overall image quality in scan 6 (image
D) is considered to be unreliable especially in the lumbar region. Note that the cortical delineation of the pedicles in image D,
especially on the right side, is indistinct which make the measurements of pedicular width difficult, uncertain and unreliable.
A B
C D
380
Radiation Dose Optimization in CT Planning of Corrective Scoliosis Surgery K. Abul-Kasim
cal CT. That dose is 49 times higher than that
of the low dose helical CT protocol of this phan-
tom study.
Even the recent reports using different dose
reduction systems record significantly higher
radiation doses than that of the here proposed
low dose CT protocol. The mean effective dose
for CT-lumbar spine after optimization was re-
ported to be 6.9 mSv in one study 14. The mean
effective dose for the same region was reported
to be 6.69 mSv after angular and z-axis modu-
lation in another study 3. These radiation doses
are 18 times higher than that of the here pro-
posed low dose helical CT which provides sig-
nificantly longer scan including most of the
thoracic and lumbar spine.
Studies have been done normalizing the ef-
fective dose to phantom age and to different
body regions (head and neck, and different
trunk regions including chest, abdomen, and
pelvis). Phantoms corresponding to six age
groups have been examined with three dif-
ferent CT scanners 15. In all cases an inverse
trend was observed between normalized effec-
tive dose and phantom age. The effective dose
normalized to age for chest examinations using
Siemens DRH-scanner increased from 6 mSv in
adult phantom to only 6.3 mSv in phantom cor-
responding a 15 year old child 15. The difference
increased even more in phantoms correspond-
ing to newborn and a one-year-old child result-
ing in normalized effective doses of 7.8 and 7.1
mSv respectively. In accordance with those re-
sults, table 4 in this study shows the effective
dose to the adult phantom (according to Monte
Carlo calculation) as well as the normalized
effective dose to the phantoms corresponding
to four different age groups, namely 15 years,
ten years, five years, and one year. However,
the last three age groups are seldom the object
for corrective surgery and consequently rarely
subjected to CT examination of the spine. The
median age of patients at or just prior to sur-
gery is estimated at 14 to 15 years 16. As the ef-
fective dose to the phantom at the age group 15
years was only 1-1.1 times higher than that of
the adult phantom (0.34-0.37 mSv versus 0.34
mSv), the results of this study are quite rep-
resentative for the estimation of the radiation
dose in CT-examinations of the spine in adult
patients as well as in patients in pubertal age
who are often the object for corrective surgery
of scoliosis. In lower age groups, e.g. in phan-
toms corresponding one year old child, the ef-
fective dose can be as high as twice the adult
dose. However the increase in the effective dose
is markedly evident in examinations with origi-
nally high radiation dose such as that of scan 1
of this study. In the here proposed low-dose CT
protocol the effective dose to a phantom corre-
sponding one-year-old child has been estimated
at 0.44-0.68 mSv – a value that still has to be
considered a relatively low dose.
A current concept has recently proposed
Table 3 The results of paired sample T-test on pedicular width measurements performed on scan 1, scan 5 and scan 6 by two
observers as well as by one observer on two different occasions. Twenty four paired sample T-tests were performed. Only the
statistically significant results are shown in this table. The statistically significant level was set at P≤0.01
Differences in pedicular width measurements (mm)
Paired differences
Sig.
(2-tailed)
Mean
(systematic
error)
Std.
Deviation
(random
error)
95% Confidence
Interval of the
Difference
Lower Upper
Pair 1 Scan 6, Observer 1, occasion 1 ----
Scan 6, Observer 2 –1,8 1,2 –2,3 –1,3 <0,001
Pair 2
Lower 5 vertebral levels: Scan 6,
Observer 1, occasion 1, ---- Scan 6,
Observer 2
–2,4 1,6 –3,5 –1,3 <0,001
Pair 3 Scan 1, Observer 2 ---- Scan 6,
Observer 2 –1,2 1,1 –1,7 –0,8 <0,001
Pair 4
Lower 5 vertebral levels: Scan 1,
Observer 1, occasion 1, ---- Scan 6,
Observer 1, occasion 1
–1,7 1,6 –0,5 –2,8 <0,009
Pair 5
Lower 5 vertebral levels: Scan 1,
Observer 1, occasion 2 ---- Scan 6,
Observer 1, occasion 2
–1,6 1,1 –0,9 –2,4 <0,001
www. centauro. it The Neuroradiology Journal 21: 374-382, 2008
381
three ways to reduce the overall radiation
dose from CT 17. These include a reduction of
the number of CT studies prescribed as well as
replacing CT examinations with other modali-
ties e.g. MRI. The role of MRI in investigating
intraspinal pathologies preoperatively is well
known in clinical practice and has been exten-
sively reviewed 18-20. In accordance with our rec-
ommendation of taking advantage of the dose
reduction system available in some scanners,
the third proposed way to reduce the popula-
tion dose from CT was to take advantage of the
automatic exposure-control option. However we
believe that serious attempts to reduce the ra-
diation dose in CT examinations and efforts to
create low dose CT protocols adapted to answer
different clinical questions have to be added to
the above mentioned methods to reduce the ra-
diation dose from CT examinations.
Applying the here proposed low dose protocol
to the CT examination of scoliotic patients who
are predominantly thinner than the phantom of
this study, will likely enable further reduction
of the radiation dose when taking advantage of
the dose reduction system of the scanner.
One limitation of this study is that it is a
phantom study and the phantom used is an
adult phantom. However when normalizing
the effective dose to phantom age (table 4), no
significant increase in the effective dose could
be recorded in the here proposed low dose pro-
tocol. The second limitation was inability to
assess the degree of vertebral rotation as this
was not built into the phantom. Another limi-
tation of this study is that the impact of ar-
tifacts from metal implants on the ability to
measure the degree of vertebral derotation and
the assessment of the hardware status after
surgery could not be evaluated. To our knowl-
edge no phantoms with either vertebral torsion
or inserted screws are commercially available
to test.
Taking the above-mentioned facts in con-
sideration, the medical community has to be
concerned about the increasing total radiation
load to the population due to the increasing
availability of the CT scan and the increasing
number of its upcoming new indications and
modifications (e.g. CT angiography, high reso-
lution studies, “multiple phase examinations”,
perfusion studies, etc.). Efforts should be con-
tinued to reduce the radiation dose of every
single CT by tailoring CT examinations with
their radiation doses individually adapted to
the purpose of the investigation.
Conclusion
This phantom study has shown that it would
be possible to reduce the radiation dose in heli-
cal CT examination of the spine in patients
planned for corrective surgery of spinal de-
formities without any significant impact on im-
age quality. To test this possibility we intend
to implement the protocol into the preopera-
tive work up of this patient category instead
of the ANV-sequential slice method used previ-
ously, provided that the radiation doses can be
kept at this low level. The results of this study
emphasize the importance of tailoring differ-
ent CT protocols with different radiation doses
adapted to answer the clinical question at is-
sue. The dose reduction system of the CT scan-
ner, if available, should be used. When assess-
ing the effective dose the absorbed dose to dif-
ferent organs (e.g. genitals and breasts) should
be taken into consideration
Table 4 The effective dose (mSv) in the adult phantom and the normalized effective dose (mSv) to the phantoms of four diffe-
rent age groups using the data from the National Radiological Protection Board (NRPB) SP250. The ranges in the age groups
other than adult represent the minimum and maximum relative doses. The median age of patients at or just prior to surgery
is estimated to be 14-15 years (16). In the here proposed low dose CT-protocol (scan 5), the normalized dose in this age group is
almost the same as that of the adults (0.34-0.37 mSv, and 0.34 mSv respectively).
Adult 15 years 10 years 5 years 1 year
Scan 1 18.6 18.6-20.46 20.46-27.9 22.32-29.76 24.18-37.2
Scan 2 08.6 8.6-9.46 9.46-12.9 10.32-13.76 11.18-17.2
Scan 3 00.49 0.49-0.54 0.54-0.73 0.59-0.78 0.64-0.98
Scan 4 00.45 0.45-0.5 0.5-0.67 0.54-0.72 0.58-0.9
Scan 5 00.34 0.34-0.37 0.37-0.51 0.41-0.54 0.44-0.68
Scan 6 00.30 0.30-0.33 0.33-0.45 0.36-0.48 0.39-0.6
382
Radiation Dose Optimization in CT Planning of Corrective Scoliosis Surgery K. Abul-Kasim
Acknowledgement
The authors gratefully acknowledge Dr. Eu-
frozina Selariu, Department of Radiology,
University of Lund, Malmö University Hospi-
tal, Sweden for her contribution in parts of the
analysis. We would also like to acknowledge
Jan Åke Nilsson, Department of Orthopedic
Surgery, University of Lund, Malmö University
Hospital for his statistical advice.
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K. Abul-Kasim, MD
Department of Radiology
Section of Neuroradiology
University of Lund
Malmö University Hospital
205 02 Malmö
Sweden
Tel.: +46 40 33 87 90
Fax: +46 40 33 87 98
E-mail: Kasim.Abul-Kasim@med.lu.se
