Transcript Pregnancy and Medical Radiation

Pregnancy and Medical
Imaging with or without
Contrast
Informed consent and
understanding
• The pregnant patient has a right to know the
magnitude and type of potential radiation
effects on a fetus that might result from inutero exposure.
2
Evaluation of potentially
pregnant patients
• In females of child-bearing age, an attempt
should be made to determine who is, or
could be, pregnant, prior to radiation
exposure.
3
Notices
• A missed period in a regularly menstruating
woman should be considered due to
pregnancy, until proven otherwise.
4
MRI SCANS
• MR Imaging is known to cause slight heating of the
body of the patient being scanned.
• There is at present no objective data to suggest that
MR Imaging has any other adverse effects on the
patient being scanned or on an unborn fetus.
• It is not possible to determine the true risk of MR
Imaging on an unborn fetus.
• MR Imaging should be avoided unless a delay until
after delivery would be dangerous to the fetus or
mother.
• If the only other means of diagnosis is with ionizing
radiation, MR Imaging would be the preferred
diagnostic study.
• MR Imaging can if necessary, be performed at any
stage in pregnancy.
5
•
•
•
•
Pregnant patients may undergo MRI scans at any
stage of pregnancy, if the ordering physician
determines the risk-benefit ratio for the patient
warrants that the study be performed.
The justification for the exam must be documented
in the patient’s hospital chart by the ordering
clinician for inpatients or emergency room patients
prior to the exam being performed.
For outpatients written documentation must be
faxed to the department by the ordering clinician
prior to the procedure being scheduled.
Gadolinium contrast will not be used during
pregnancy without prior approval by a radiologist
6
Fetal radiation risk
• There are radiation-related risks throughout
pregnancy that are related to the stage of
pregnancy and absorbed dose.
• Radiation risks are most significant during
organogenesis in the early fetal period,
somewhat less in the 2nd trimester, and least in
the 3rd trimester.
Most
risk
Less
Least
7
Radiation-induced malformations
• Malformations have a threshold of 10-20 rad
or higher and are typically associated with
central nervous system problems.
8
Central nervous system effects
• During 8-25 weeks post-conception the CNS is
particularly sensitive to radiation.
• Fetal doses in excess of 10 rad can result in some
reduction of IQ (intelligence quotient).
• Fetal doses in the range of 100 rad can result in
severe mental retardation and microcephaly,
particularly during 8-15 weeks and to a lesser
extent at 16-25 weeks.
• The accepted maximum cumulative fetal dose
during pregnancy is 5 rad.
9
Breast Feeding and Contrast
• An infant absorbs approximately 0.01% of the maternal intravenous
dose of iodinated contrast from breast milk, over the first 24 hours
(equivalent to less than 1% of the recommended dose for an infant
undergoing a contrasted imaging study). The ACR recommends that it
is safe to breast feed immediately after an iodinated study or she may
wait 24 hours, if she continues to be concerned about potential risk.
• An infant absorbs approximately 0.0004% of the maternal intravenous
dose of gadolinium contrast from breast milk, over the first 24 hours
(equivalent to less than 0.04% of the recommended dose for an infant
undergoing a contrasted imaging study). The ACR recommends that it
is safe to either breast feed immediately after a gadolinium contrast
study or she may wait 24 hours, if she continues to be concerned about
potential risk.
10
Use of contrast (iodinated or gadolinium)
during pregnancy is recommended only if:
1.
2.
3.
4.
The referring physician feels that the information gained
by imaging with a contrasted study cannot be obtained
by an alternative method.
The results will not affect the patient/fetus during the
pregnancy.
Waiting after the pregnancy to obtain this information is
not prudent for the patient’s/fetus’ care.
Documentation is made on the patient’s chart by the
referring physician who has approved informed consent.
–
“ACR Manual on Contrast Media (Version 5.0)”
11
Common Radiographic
Studies
12
Examination type
Estimated fetal dose
per examination (rad)*
Number of
examinations
required for a
cumulative 5-rad
dose+
Skull
0.004
1,250
Dental
0.0001
50,000
Cervical Spine
0.002
2,500
Upper or Lower Extremity
0.001
5,000
Chest (two views)
0.00007
71,429
Mammogram
0.020
250
Abdominal (multiple views)
0.245
20
Thoracic Spine
0.009
555
Lumbosacral spine
0.359
13
Intravenous pyelogram
1.398
3
Pelvis
0.040
125
Hip (single view)
0.213
23
Plain Films
13
Examination type
Estimated
Number of examinations
fetal dose
required for a cumulative
per
5-rad dose+
examination
(rad)*
CT scans 9slice thickness: 10
MM) Non-helical
Head (10 Slices)
<0.050
>100
Chest (10 slices)
<0.100
>50
Abdomen (10slices)
2.600
1
Lumbar Spine (5 slices)
3.500
1
Pelvimetry (1 slice with scout film)
0.250
20
14
Examination type
Estimated fetal
dose per
examination
(rad)*
Number of examinations
required for a cumulative
5-rad dose+
Upper GI Series
0.056
89
Barium Swallow
0.006
833
Barium Enema
3.986
1
Most studies using technetium (99mTc)
<0.500
>10
Hepatobiliary technetium HIDA scan
0.150
33
Ventilation-perfusion scan (total) 0.215
0.215
23
Perfusion portion:
Technetium
.0175
28
Ventilation portion: xenon (133 Xe)
0.040
125
Iodine ( I 131 ), at fetal thyroid tissue
590.000
Iodine (I 131) is
contraindicated during
pregnancy
Fluoroscopic studies
Nuclear medicine studies
Examination type
Estimated
fetal dose per
examination
(rad)*
Number of examinations
required for a cumulative 5-rad
dose+
0.100
N/A
Environmental sources (for
comparison)
Environmental background
radiation (cumulative dose over
nine months)
CT= computed tomographic; GI=gastrointestinal; HIDA=hepatobiliary
iminodiacetic acid; N/A= not applicable
*--Where the reference provides a range of estimated doses, the highest value of the
range listed here.
+--Authors’ calculation from data provided in reference: values rounded to lowest
whole number.
16
Chest for Pulmonary
Embolism
CT Helical
Scan
Estimated fetal dose per examination (rad)
1st Trimester
2.5 mm slice
.00033 –.00202
2nd Trimester
.00079-.00767
3rd Trimester
.000513-.001308
17
Helical CT Scans
Single Slice
(5 mm thick)
Multi-Slice
(4) Detector
(5 mm thick)
Abdomen
1.25 – 3.5 rad
1.25 – 3.5 rad
Pelvis
1.25 – 3.5 rad
1.25 – 3.5 rad
18
Nuclear medicine and
pregnant patients…
•
•
•
Most diagnostic procedures are done with shortlived radionuclides (such as technetium-99m) that
do not cause large fetal doses
Often, fetal dose can be reduced through maternal
hydration and encouraging voiding of urine
Some radionuclides do cross the placenta and can
pose fetal risks (such as iodine-131)
19
Nuclear medicine and
pregnant patient (cont’d)
•
The fetal thyroid accumulates iodine after about
10 weeks gestational age
•
High fetal thyroid doses from radioiodine can
result in permanent hypothyroidism
•
If pregnancy is discovered within 12 hours of
radio-iodine administration, prompt oral
administration of stable potassium iodine (60130 mg) to the mother can reduce fetal thyroid
dose. This may need to be repeated several times
20
Approximate whole body fetal dose (rad) from
common nuclear medicine procedures
Activity
(MBq)
Early
pregnancy
9 months
750
240
0.47
0.09
0.18
0.09
Liver colloid scan
Thyroid scan
300
400
0.06
0.44
0.11
0.37
Renal DTPA
Red blood cell
300
930
0.9
0.6
0.35
0.25
I123 thyroid uptake
30
0.06
0.03
0.004
0.015
Procedure
Tc-99m
Bone scan
Lung scan
I131 thyroid uptake
0.55
Nuclear medicine and breast feeding
•A number of radionuclides are excreted in breast milk. It is
recommended that breast feeding is suspended as follows:
– Completely after I131 therapy
– 3 weeks after I131, I125, Ga67, Na22, and Tl201
m
– 12 h after I131 hippurate and all 99 Tc compounds except
as below
– 4 h after 99mTc red cells, DTPA, and phosphonates
22
Conversions for Absorbed Dose
•
•
•
•
•
•
•
0.001 rad = 1 mrad = 0.01 mGy
0.01 rad = 10 mrad = 0.1 mGy
0.1 rad = 100 mrad = 1 mGy = 0.001 Gy
1 rad = 1000 mrad =10 mGy = 0.01 Gy
10 rad = 100 mGy = 0.1 Gy
100 rad= 1000 mGy = 1 Gy (Gray)
1000 rad = 10 Gy
23
Termination of pregnancy…
• High fetal doses (100-1000 mGy, 10-100 rad)
during late pregnancy are not likely to result in
malformations or birth defects since all the organs
have been formed
• At fetal doses in excess of 500 mGy (50 rad),
there can be significant fetal damage, the
magnitude and type of which is a function of dose
and stage of pregnancy
• At fetal doses between 100 and 500 mGy (10 and
50 rad), decisions should be based upon individual
circumstances
24
Reference List
• ICRP Publication 84, Task Group: R. Brent, F. Mettler, L.
Wagner, M. Berry, S. He, T. Kusama
• Safety of Radiographic Imaging during pregnancy. Kevin
S. Toppenberg, M.D., Ashley Hill, M.D. and David Miller
M.S. Florida Hospital Medical Center. Orlando, Florida.
• Policy for Handling Pregnant Patients. Georges Y. ElKhoury, M.D. and Mark Madsen, Ph.D., The University of
Iowa Hospitals and Clinics, Department of Radiology.
• Pulmonary Embolism in Pregnant Patients: Fetal
Radiation Dose with Helical CT, Helen T. Winer-Muram,
M.D. et al, Indiana Univ. School of Medicine, Dept. of
Radiology.
25
Web sites for additional information on
radiation sources and effects
•
European Commission (radiological protection pages):
europa.eu.int/comm/environment/radprot
•
International Atomic Energy Agency:
www.iaea.org
•
International Commission on Radiological
Protection:
www.icrp.org
•
United Nations Scientific Committee on the Effects
of Atomic Radiation:
www.unscear.org
•
World Health Organization:
www.who.int
26