












































International Journal of Cancer Therapy and Oncology
www.ijcto.org

Corresponding author: Aida Mhiri; Department of Nuclear Medicine, Salah Azaiez Institute, Tunis, Tunisia.
Cite this article as: Mhiri A, Slim I, Slimène M. Dosimetry estimation of SPECT/CT for iodine 123-labeled metaiodobenzylguanidine in children. Int J Cancer
Ther Oncol 2015; 3(3):323. DOI: 10.14319/ijcto. 33.3

© Mhiri et al. ISSN 2330-4049

Dosimetry estimation of SPECT/CT for iodine 123-labeled
metaiodobenzylguanidine in children

Aida Mhiri, Ihsen Slim, Mohamed Faouzi Slimène

Department of Nuclear Medicine, Salah Azaiez Institute, Tunis, Tunisia

[Presented at the 4th African Regional IRPA congress (AFRIRPA04), which was held from September 13-17, 2014 in Rabat, Morocco. This paper
was reviewed and accepted by the scientific committee of the 4th African Regional IRPA congress]

Conference Proceeding

Abstract
Purpose: To evaluate the additional radiation exposure in terms of effective dose incurred by patients in the CT (computed to-
mography) portion of 123I-MIBG (123II-metaiodobenzylguanidine) study with SPECT/CT (Single photon emission computed
tomography associated to computed tomography) in some pediatric patients of our department. Methods: Data from
123II-MIBG scans comprising 50 children were presented in this study. The contribution of total effective dose imparted by the
nuclear tracer and patient's age was calculated. Effective dose from the CT portion of the examination is also estimated. SPECT
acquisitions were performed with a dual-headed SPECT unit with an integrated 2-slice CT scanner (Symbia T E-Cam, Siemens
Medical Systems, Erlangen, Germany). The CT acquisition were performed using a tube current modulation system (Care Dose
4D). Parameters used were: tube current of 30 - 60 mAs, slice thickness of 3-5 mm, and tube voltage of 110 kV. Results: Our
results show that SPECT dosimetry depends on administered activity and patient’s age and weight. For CT scan, effective dose is
affected by tube current (mA), tube potential (kVp), rotation speed, pitch, slice thickness, patient mass, and the exact volume of
the patient that is being imaged. Conclusion: For children, 123II-MIBG study with SPECT/CT should be performed using the
lowest available voltage and current. A sensible choice of these two parameters used can significantly reduce radiation dose,
without any compromise in the quality of the diagnostic information.

Keywords: 123II-Metaiodobenzylguanidine; SPECT-CT- Pediatric; Dosimetry

Introduction
Metaiodobenzylguanidine (MIBG) is used for scintigraphic
imaging of the adrenomedullary tumors pheochromocytoma
and neuroblastoma in children. The use of I23I-l for labeling
takes advantage of the better physical properties of I23I for
imaging, allows higher activities to be administered with
favorable radiation dosimetry and greater photon flux re-
sulting in higher count, higher quality planar images and
permits the performance of the single photon computed to-
mography (SPECT).1-3 Single photon emission computed
tomography associated to X-ray computed tomography
(SPECT/CT) is a nuclear medicine tomographic imaging
technique which improves diagnostic accuracy for particular
clinical indications due to the possible attenuation and/or
scatter correction of the SPECT functional images and the
availability of helpful anatomic information.4

Also, the interpretation of scintigraphic images can be con-
founded by physiological uptake, which can be better identi-
fied with SPECT/CT. However, it results in a significant in-
crease of patient dose. In fact, according to literature data
SPECT/CT compared to SPECT alone causes more radiation
to the patient which is not sufficient to cause deterministic

effects.2, 4, 5, 6 For SPECT effective dose depends on adminis-
tered activity and patient’s age. The average radiopharma-
ceutical effective dose varies from tens to thousands of mSv
for some nuclear medicine exams.4 However, the introduc-
tion of CT in nuclear diagnostic process results in a signifi-
cant increase of the patient dose. In general, effective dose
(E) for CT examinations can be higher than most other di-
agnostic imaging modalities6. Some authors have questioned
the need to reduce doses particularly in children.7-8

Understanding radiation dosimetry and its potential for del-
eterious health effects, having knowledge of the magnitude
of the effective dose and the dose to specific organs from
SPECT and CT, and considering the role of CT in the context
of SPECT/CT will allow the reader to reduce the radiation
dose to the patient without compromising the quality of the
patient’s care.9 In this article, we will present the dosimetry
associated with pediatric SPECT/CT for iodine 123-labeled
metaiodobenzylguanidine, in terms of effective dose, in some
pediatric patients of our department. Factors affecting the
radiation dose associated with SPECT, using 123II-MIBG in
children will be described. The dosimetry associated with

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2 Mhiri et al.: SPECT-CT dosimetry for iodine 123-labeled metaiodobenzylguanidine International Journal of Cancer Therapy and Oncology
www.ijcto.org

© Mhiri et al. ISSN 2330-4049

the CT component will be also noted.

Methods and Materials
Data from 123II-MIBG scans comprising 50 children aged
between 1 and 10 years, were presented in this study. The
contribution of total effective dose imparted by the nuclear
tracer and patient's age was calculated. Effective dose from
the CT portion of the examination is also estimated.

SPECT acquisitions were performed with a dual-headed
SPECT unit with an integrated 2-slice CT scanner (Symbia T
E-Cam, Siemens Medical Systems, Erlangen, Germany). The
CT acquisition were performed using a tube current modula-
tion system (Care Dose 4D). Parameters used were: tube
current of 30 - 60 mAs, slice thickness of 3-5 mm, and tube
voltage of 110 kV.

For each child the CT was acquired immediately after
SPECT; the patient being kept in the same position to mini-
mize offsets due to movement and allow proper registration
on fused imaging. The contribution of total effective dose
imparted by the nuclear tracers for each child was calculated
by multiplying the average administered activity for all pa-
tients by the “effective dose per unit administered activity”
conversion factors listed in the International Commission on
Radiological Protection (ICRP) Publication 53 7 and 80 10-11.
The effective dose from the CT portion of the examination is
estimated from the product of the dose length product (DLP)
and a body-region-specific conversion factor, k (mSv mGy-1
cm-1), which take into account the varying biological sensi-
tivities of different organs as given in Table 1.12

DLP is a patient-specific value determined by the scan
length and the acquisition parameters; it represents the total

amount of radiation delivered in the acquisition. CT scan
was acquired immediately following completion of the
SPECT study with the child in the same position to minimize
motion errors.

Results
While for SPECT, dosimetry is dependent on administered
activity and the patient’s age and weight; for CT scan, there
are many factors which affect dosimetry. Dose estimates
(Table 2) are dependent on tube current (mA), tube potential
(kVp), rotation speed, pitch, slice thickness, patient mass,
and the exact volume of the patient that is being imaged.
According to the literature data, for children, MIBG imaging
can be performed using the lowest available voltage and
current.

Discussion
According to Gelfand 13 and Fahey 9, combined imaging re-
sults in a significant increase of the patient dose. Effective
dose is directly dependent on administered activity and the
patient’s age for SPECT; whereas as described by Mhiri 14, for
CT scan, it depends on tube current, tube potential, rotation
speed, pitch, slice thickness, patient mass, and the exact
volume of the patient that is being imaged. A sensible choice
of these parameters used, can significantly reduce radiation
dose, without any compromise in the quality of the diagnos-
tic information, according to Piwowarska 15 and Larking 5.
The dose in the patient must be as low as compatible with
the medical purpose. For Larkin 5 and Valentin 7, practice
leading to a medical exposure must be clearly justified and
protection against radiation must be optimized, particularly
for children. Also, quality control procedures have to be
defined because of the coupling between the two devices.16

TABLE 1: Factors for DPL/effective dose Conversion over various body regions and patient ages.12

Region of body Effective dose per DLP (mSv (mGy cm)-1) by age
< 1-year-old 1-year-old 5-year-old 10-year-old

Head and neck 0.013 0.0085 0.0057 0.0042
Head 0.011 0.0067 0.0040 0.0032
Neck 0.017 0.012 0.011 0.0079
Chest 0.039 0.026 0.018 0,013
Abdomen and pelvis 0.049 0.030 0.020 0.015
Trunk 0.044 0.028 0.019 0.014

TABLE 2: Effective doses (E) delivered by 123 I-MIBG SPECT-CT scintigraphy over patient ages and body regions.

SPECT portion CT portion SPECT-CT examination

Average Ac*
(MBq/kg)

Average E*
(mSv)

Average E*
(mSv)

E over regions (mSv)
Total E*
(mSv)

% increase of E* by
the

inclusion of the CTTrunk Abd

1-year-old 6 3.4 1.72 1.44 1.98 5.12 50%
5-year-old 5 4.4 1.24 1.20 1.34 5.64 28%
10-year-old 5 4.1 1.36 1.24 1.51 5.46 33%

*Ac = Activity; *E = Exposure



Volume 3 • Number 3 • 2015 International Journal of Cancer Therapy and Oncology 3
www.ijcto.org

© Mhiri et al. ISSN 2330-4049

Conclusion
Compared to planer images, 123I-MIBG study with
SPECT/CT increases significantly the number of lesions de-
tected and allows better anatomic localization of neuroblas-
toma deposits and delineation of normal bowel activity.
However, patient dose increases significantly also. Then,
reducing the patient dose should be a constant preoccupation
of prescribing physician, nuclear physician's and qualified
personnel performing the act, particularly for child. Every
effort should be made to adhere to the “As Low as Reasona-
bly Achievable (ALARA)” principle and ensure that the pa-
tient is not subjected to unnecessarily high levels of radia-
tion, still more at young age.

Conflict of interest
The authors declare that they have no conflicts of interest.
The authors alone are responsible for the content and writ-
ing of the paper.

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