METHODS
Embryo/fetal doses were estimated for 74 pregnant women underwent SPECT/CT scan from different
regions of Turkey. OLINDA/EXM package program was used for radiation dose calculation from internal
emitters, while CT dose was calculated from modified soft-tissue CT dose index.
RESULTS
The highest embryo/fetal dose was found in 99mTc- methoxy isobutyl isonitrile (MIBI) myocardial perfusion
scintigraphy (MPS) as (8.88+5.55=14.43 mGy) from both distinct modes (stress and rest imaging).
The embryo/fetal dose from MPS slightly increased to 15.63 mGy with the CT dose contribution.
Whereas, 99mTc- dimercaptosuccinic acid (DMSA) static renal scintigraphy recorded the lowest embryo/
fetal dose among the other diagnostic procedures (mean 1.06 mGy).
CONCLUSION
The embryo/fetal doses increased with simultaneous CT scans in nuclear medicine modalities. Questioning
pregnancy before scintigraphy is obligatory the first-line strategy to avoid radiation exposure risks.
Keywords: Embryo/fetal dose; fetus dose; International Commission on Radiological Protection 84; SPECT radiopharmaceuticals; <sub>99m</sub>Tc radiopharmaceuticals
In the same framework, radiation dose assessment
of embryo/fetal has increasingly gained a great
concern in nuclear medicine practices through dose
computation and risk estimation. In common practice,
different types of radioisotopes and wide range
of radioactivity are utilized for diagnostic and therapeutic
purposes that might exceed the tolerated fetus
dose. Hence, developing precise methods to precisely
benchmark radiation dose to embryo/fetus are of
great importance with respect to the radiation protection
legislations. These models should inherently take into account the transfer of radionuclides across
the placenta, distribution and retention of the radionuclides
in embryonal/fetal tissues, growth of the
embryo/fetal, and photon irradiation sources in the
placenta and maternal blood.[
In general, prenatal radiation exposure of approximately
10 mGy might enhance the risk of fetal disorders
such as prenatal death, microcephaly, reduced
intelligence quotient, organ malformation, mental
retardation, intrauterine growth retardation, and
childhood cancers. However, it was reported that radiation
dose <50 mSv (5 rem) is not associated with
fetal anomalies emergence or pregnancy loss.[
Since, many radiopharmaceutical agents are in use
for the nuclear investigations, the variation in radionuclides
biokinetics and excretion rate is impossible to
consider within the fetal dose estimation process.[
This study was dedicated to calculate fetal absorbed
dose in pregnant women subjected to SPECT scan with
99mTc-labeled radiopharmaceuticals. A further goal was
to compare the fetus dose values generated from the
mentioned procedures with the risk thresholds reported
by ICRP 84.
Between June 2015 and June 2021, embryo/fetal doses of 74 pregnant women underwent SPECT scans were calculated retrospectively. Gestational age was obtained from patients" specific ultrasound data. Accordingly, 68 (92%) women were in the first trimester of pregnancy and 6 (8%) were in the second trimester of pregnancy.
All pregnant women were asked to bring the essential documents that contain detailed information about the type of procedure. OLINDA/EXM 1.0 software was used to calculate embryo/fetal dose according to the following MIRD schema:
where D is absorbed dose in a target organ (mGy),
à is cumulated activity in a source organ (MBq • h), A0
is administered activity (MBq), 𝜏 is residence time (h),
S is dose factor provided in the program 
Individual embryonal/fetal dosimetry is not applicable,
as no pre-imaging procedures could be tried for
specific dosimetry. Attempt was made to use fetus kinetic
data generated from phantom study reported by
Russell et al.[
A set of equations was used to estimate the CT related
dose following SPECT/CT examinations. The calculated
dose values from CT were added to that obtained from
SPECT and given as a total SPECT/CT embryo/fetal
dose in the results section. FetDose V4 computer software
was used to compute the fetal absorbed dose.[
The fetal dose (Df) from CT scans was calculated
using the formula (2) as seen below:
where CTDI is CT dose index and CTDIsoft tissue
(mGy/100 mAs) is the CTDIair to the ICRU muscle
(CTDIsoft tissue=CTDIair x 1.07) used as approximations
for the dose to soft tissue within the body and NUDV
is the sum of the normalized doses for all 5 mm slabs
lying within the scan volume.[
In contrast, 99mTc-diethylene triamine pentaacetic
acid (DTPA) is rapidly distributed throughout the extracellular
fluid space following intravenous injection,
while the most of the activity accumulates in the kidneys
and excreted out through the urinary bladder. The
average dose of embryo/fetal for three pregnant women
underwent dynamic renal scintigraphy with 99mTc-DTPA
was 2.48 mGy. In another study, fetal dose values
for 99mTc-DTPA scan were calculated as 1.66 mGy for
<3 months of pregnancy.[
On the other hand, ICRP Publication 84 stated that
radiation-induced malformation has a threshold of
50-100 mGy (5-10 rad). A serious fetal damage might
occur when embriyo/fetal doses exceed 500 mGy (50
rad) taking into consideration the radiation type and
stage of pregnancy.[
Eventually, the diagnostic nuclear medicine examinations
often induce fetal dose less than the pregnancy
terminating dose threshold (100 mGy) reported
by ICRP 84. To be remembered, radiation exposure
may develop deterministic and stochastic effects on
the fetus. The deterministic effects are dose-correlated
and lead to distinct damage or mutations in the fetus
DNA genes. However, the stochastic effect has no dose
threshold ensuring possible side effects even with small
doses.[
To this end, 99mTc-labelled agents are short lived radiopharmaceuticals
and fetal dose exceeding 100 mGy
from a single procedure is impossible. Thus, teratogenic
consultation is distinctly recommended and medical
aborts decision can be made in cooperation with family,
obstetrician, and medical physicist.
Peer-review: Externally peer-reviewed.
Conflict of Interest: All authors declared no conflict of interest.
Ethics Committee Approval: The study was approved by the İstanbul University Cerrahpaşa Faculty of Medicine Ethics Committee (No: 219488, Date: 09/07/2015).
Financial Support: None declared.
Authorship contributions: Concept - N.İ.I., M.D.; Design - N.İ.I.; Supervision - N.İ.I., M.D.; Funding - M.D., N.İ.I.; Data collection and/or processing - M.D., N.İ.I.; Data analysis and/or interpretation - M.D., N.İ.I; Literature search - M.D., N.İ.I; Writing - N.İ.I.; Critical review - M.D.
