DIVISION OF DIAGNOSTIC
RADIOLOGY
Georges Y. El-Khoury, M.D.
and Mark Madsen, Ph.D.
PURPOSE: To provide an
appropriate policy for handling pregnant or possibly pregnant patients
requiring diagnostic examinations that involve ionizing radiation.
BACKGROUND: Available scientific data
shows that the health risks associated with radiation to the fetus are small
for the dose levels delivered by most diagnostic procedures. Extrapolations from high dose exposures puts
the risk of radiation induced congenital defects at the level of 0.5-1%/rem(1-4). However, no
proven effects have been observed for total radiation doses to the fetus less
than 5 rem(5, 6). It is
important to keep in mind that the average background radiation in the U.S.A.
is approximately 0.3 rem/year and the maximum allowable dose to the fetus of
declared pregnant radiation workers is 0.5 rem (10 CFR 20.1208). The natural incidence of congenital defects
when the fetus has not been exposed to radiation is estimated at 5% (7).
The radiation dose to the fetus from diagnostic procedures when the fetus is not in the x-ray beam is approximately the same as the daily background radiation dose received by the average American (approximately 0.001 rem). Diagnostic studies in which the fetus is in the x-ray beam result in substantially higher doses. Examinations such as KUB, flat and upright views of the abdomen, lumbralsacral spine examination and limited intravenous urogram typically deliver less than 1 rem to the fetus (5)(See Appendix A). Examinations where the fetus can receive a radiation dose greater than 1 rem include barium enema, CT studies of the abdomen and pelvis, and diagnostic or interventional procedures involving lengthy fluoroscopy with multiple filming of the pelvis and abdomen(5) (See Appendices B & C).
The health risks associated with radiation to the fetus are cumulative. As a result, previous exposures to radiation during the pregnancy must be considered before new procedures are initiated.
Our primary goal is to protect the well being of the mother because her well being preserves the life of the fetus also. In achieving this goal, every attempt should be made at keeping the radiation dose to the fetus to a minimum.
POLICY: I. As stated in the Hospital Formulary, the Radiology Department should be notified when a patient is known or thought to be pregnant. This information should be included on the x-ray requisition (the D-2 Form) or entered electronically on the order entry screen.
II. Before every imaging or interventional procedure, the technologist should inquire from all female patients, in the child bearing age, as to whether she is, or may possibly be pregnant. If the patient is too sick to answer questions, the technologist should ask the family or treating physician. If all attempts do not result in a clear answer, if time permits a pregnancy test should be performed.
III. If a patient responds that she is or may be pregnant, the radiologist assigned or scheduled for that particular service should always be contacted.
There are four possible scenarios to be considered:
A. For examinations above the abdomen or below the hips, the patient should be assured that there is no scientific evidence that the examination will result in any detectable harm to the fetus. Shielding of the abdomen and pelvis with lead aprons should be used if feasible.
B. For examinations where the fetus is in the direct beam and the estimated dose calculated from Appendix A, B or C is less than 1 rem, the radiologist should discuss the benefits versus the risks of the procedure with the referring physician. Imaging techniques not involving ionizing radiation should be considered. If the examination is judged to be appropriate and necessary, the clinician responsible for the care of the patient will write a note in the chart stating that the imaging study is indicated for the management of the patient. The radiologist will explain the procedure to the patient with the assurance that the radiation dose will be kept as low as possible consistent with obtaining the required diagnostic information.
C. For examinations where the fetus is in the direct beam and the estimated dose calculated from Appendix A, B or C is greater than 1 rem but less than 5 rems, the radiologist and referring physician should work together to find options that will provide the needed information without the use of ionizing radiation such as ultrasound or MRI. If the radiological procedure is deemed essential, the patient should be involved in the decision to proceed with the examination. She should be informed by the radiologist of the risks and benefits of the diagnostic test or interventional procedure. The patient will be asked to sign an informed consent form (Appendix D). The clinician responsible for the care of the patient will write a note in the chart stating that the test is indicated for the management of the patient.
D. For the rare occasion where the estimated dose to the fetus exceeds 5 rems, a formal calculation of the dose will be conducted by a radiation physicist (8). The patient and/or family should be counseled about the risks to the fetus. The referring physician, the radiologist and radiation physicist should all write notes in the patient’s chart explaining the circumstances and medical justification for the examination or procedure.
The patient will be asked to sign an informed
consent form (Appendix E).
IV. Technical Principles to be Followed in every Pregnant Patient
A. Limit exposures to those that are essential for a diagnosis.
B. Use precise collimation and pelvic shielding whenever possible.
C. Limit fluoroscopy to short bursts as needed. All fluoroscopic procedures must be timed and a written record of the fluoroscopy time, kVp and mA must be kept.
D. Every effort must be made to eliminate repeat exposures resulting from technical errors. Repeat exposures should not be performed without consulting with the radiologist responsible for the patient.
E. For CT examinations of the abdomen and pelvis, the slice thickness must not go below 5 mm. The pitch should be increased as much as possible. The mAs and kVp should be reduced to the lowest level judged by the radiologist to yield a diagnostic study.
F. The average power setting for ultrasound studies in the vicinity of the fetus must be kept to a minimum consistent with achieving a diagnostic study.
G. The IRPA (International Radiation Protection Association) recommends that elective MRI examinations should be postponed until after the first trimester.
H. All contrast media should be used with caution in pregnant women.
References
1. Miller RW, Blot WJ. Small head size after in-utero exposure to atomic radiation. Lancet 1972; 2: 784-7.
2. MillerRW, Mulvihill JJ. Small head size after atomic irradiation. Teratology 1976; 14: 355-7.
3. Otake M, Schull WJ. Radiation-related brain damage and growth retardation among the prenatally exposed atomic bomb survivors. Int J Radiat Biol 1998; 74: 159-71.
4. Schull WJ, Otake M. Cognitive function and prenatal exposure to ionizing radiation. Teratology 1999; 59: 222-6.
5. Wagner L
Lester R, Saldana L. Exposure of the Pregnant Patient to
Diagnostic Radiations : A Guide to
Medical Management. 2nd ed. 1997, Madison: Medical Physics Publishing Corp. 259.
6. Otake M., Schull WJ, Lee S. Threshold for radiation-related severe mental retardation in prenatally exposed A-bomb survivors: a re-analysis. Int J Radiat Biol 1996; 70: 755-63.
7. Hall E. Radiobiology for the Radiologist. 5th ed. 2000, New York: Lippincott Williams & Wilkins Publishers;. 588.
8. Mann FA, Nathens A, Langer SG, Goldman SM, Blackmore CC. Communicating with the family: the risks of medical radiation to conceptuses in victims of major blunt-force torso trauma. J Trauma 2000; 48(2):354-7.
Estimated
fetal dose for a single radiographic view of the abdomen or pelvis with the
fetus in the field of view.
Patient Estimated Dose(rem)
Thickness(cm) AP View Lateral
View
14-15
0.1
0.07
16-19
0.15 0.10
20-23
0.21
0.15
24-26
0.31 0.2
27-30
0.43
0.3
31-34
0.56
0.4
Estimated
fetal dose for fluoroscopy of the abdomen or pelvis with the fetus in the field
of view.
0.7
rem/minute (80 kVp and 2 mA)
This
is based on measured values of 2.5 R/min at the tabletop of the fluoroscopic
unit.
Estimated
fetal dose for CT of the abdomen or pelvis with the fetus in the field
120 kVp, slice thickness greater than or equal to
5mm*
(4 detector) Single slice helical CT
Technique Dose(rem) Technique Dose(rem)
300
mAs, pitch 4.5 3.5 300 mAs, pitch 1 3.5
300
mAs, pitch 6.5 2.5 300 mAs, pitch 1.5 2.5
200
mAs, pitch 4.5 2.3 200
mAs, pitch 1 2.3
200
mAs, pitch 6.5 1.5 200
mAs, pitch 1.5 1.5
150
mAs, pitch 4.5 1.75 150 mAs, pitch 1
1.75
150
mAs, pitch 6.5 1.25 150 mAs, pitch 1.5
1.25
Below 5 mm on the multislice CT systems, the penumbra of the x-ray beam results in increased dose. The increase for 3 mm slices is 10-20%, the increase for 1 mm slices is 30-40% and the increase for 0.5 mm slices is 50-150% depending on the manufacturer.
Consent Form for Imaging of the Abdomen or Pelvis in Pregnancy where the Dose is 1-5 rem
Consent Form for Imaging of the Abdomen or Pelvis in Pregnancy where the Dose more then 5 rem