Radiation protection in pregnancy

RADIATION PROTECTION
IN PREGNANCY
Victor Ekpo
MSc Medical Physics, 2017
RADIODIAGNOSIS NUCLEAR MEDICINE RADIOTHERAPY

OUTLINE
• Introduction
• General Principles of Radiation Protection
• Occupational Exposure of Pregnant Employees
• Medical Exposure of Pregnant Patients
• Pregnancy in Radiodiagnosis (incl. 10-day rule)
• Pregnancy in Radiotherapy
• Pregnancy in Nuclear Medicine
• Foetal Dose Estimation
• Conclusion
Victor Ekpo, Radiation Protection in Pregnancy, 2017

INTRODUCTION
• Foetuses are more sensitive to radiation than adults.
• Radiation exposure thus portends some risk to the foetus, as it is a known:
• Teratogen: agent that can disturb the development of the embryo or foetus.
Teratogens can halt pregnancy or produce a congenital malfunction.
• Carcinogen: can cause cancer.
• Mutagen: can cause genetic mutation.

TYPES OF EXPOSURE
• Planned/Medical Exposures:
• Radiodiagnosis (X-ray, CT, Fluoroscopy)
• Nuclear Medicine
• Radiotherapy (esp. breast, thyroid or cervical cancers)
• Occupational exposures for pregnant employees
• Accidental exposure in pregnancy
Fig: A caution sign on the X-ray
room door for pregnant women at
Afriglobal Radiology, Lagos

GENERAL PRINCIPLES OF
RADIATION PROTECTION
• Justification
• “No practice shall be adopted unless its introduction produces a positive
net benefit.”
• Optimization
• Follows ALARA Principle: the dose to the patient should be the lowest
necessary to achieve the clinical aim.
• Limitation of Doses
• The total dose to any individual from regulated sources in planned
exposure situations (other than the medical exposure of patients) should
not exceed the appropriate limits recommended by the ICRP.

JUSTIFICATION FOR PREGNANT PATIENTS
If patient is pregnant or likely to be:
• Can examination be done without utilizing radiation?
• Can examination be deferred until after delivery?
• Does delaying exam involve greater risk to patient?
• If procedure must be undertaken, the foetal dose must be kept
minimum.

10-DAY RULE
If it is unclear whether or not patient is pregnant, the 10-day rule for women of
reproductive age should be adopted, esp for high dose procedures (e.g. fluoroscopy,
pelvic CT).
The ICRP states the 10-day Rule thus:
This 10-day rule has been amended to permit radiographic examination of female
patients of reproductive age, provided the patient is not pregnant. (Jumah, 1992).
“Whenever possible, one should confine the radiological
examination of the lower abdomen and pelvis to the 10-day interval
following the onset of menstruation”

10-DAY RULE (contd.)
• The 10-day rule is linked to the teratogenic effect of radiation.
• The responsibility for pregnancy determination lies with the
referring physician, radiographer or radiologist or technician.
• Date of last menstrual period (LMP) should be requested from
the patient, and clearly stated on a request form to aid in
determination.

PRE-CONCEPTION IRRADIATION OF GONADS
• Pre-conception irradiation of either parent’s gonads has NOT been shown to result
in increased risk in children.
• High doses to the testes or ovaries can however result in temporary or permanent
sterilisation, esp. in radiotherapy.
• General advice is thus that gonads should be shielded from external radiation. A
woman’s ova are formed early in life and radiation exposure may lead to genetic
damage expressed in future generations.
• Testicular shields may be used to reduce the gonad dose, although the benefit is
small.

FACTORS AFFECTING FOETAL RISK
• Dose: High dose procedures give higher dose to foetus, and thus
higher risk.
• Stage of Gestation: Risk is most significant during
organogenesis, less in 2nd trimester, least in 3rd trimester.
• Dose Rate: Higher dose rates give higher foetal dose.

STAGES OF GESTATION
• Pre-Implantation: Day 1 - 10
• Organogenesis: Weeks 3 – 7 *Weeks are gestation weeks (GW) or postconception (PC).
• Growth/Foetal Stage: Week 8 – birth
Less Least
Most
risk
Organogenesis 8-17 GW > 25 GW

PRE-IMPLANTATION (<10 DAYS)
• Fertilization of egg and implantation in wall of uterus occurs during this
period.
• The embryonic cells are rapidly growing and not well differentiated.
• If exposed to radiation, it is all or nothing.
• Either the embryo fails to implant and dies; or it is unaffected and survives
without any risk of malformation.

ORGANOGENESIS (WEEK 3 - 7)
• Embryonic tissues are now differentiating into major organs.
• A dose >100 mGy may lead to death of embryo or
malformations.
• Conceptus is at most risk at this stage.

FOETAL PERIOD (WEEK 8 - BIRTH)
• Characterized by rapid growth of foetus
• The Central Nervous System (CNS) is most sensitive at 8 -25 GW.*
• The CNS of a foetus at 8-25 GW may be affected unfavorably at doses ≥ 100 mGy.
• Foetus is sensitive to mental retardation.
Foetal doses > 100 mGy can result in lower IQ
Foetal doses > 1000 mGy can result in severe mental retardation,
esp. in 8 -17 weeks, but less between 16 – 25 weeks.
• So does the risk of microcephaly or small head size (SHS).

FOETAL PERIOD (contd.)
• During the 8th -17th GW, the number of neurons in developing brain
increases rapidly and neurons move into specific part of brain.
• This high rate of mitotic activity explains the high degree of
radiosensitivity in the 8th to 17th week.
• After 17th week, no further cell division occurs in the foetus’ brain.
• In utero irradiation later than 25th GW does not affect the IQ of the child.
• High foetal doses (100 – 1000 mGy) during late pregnancy (>25 GW) are
not likely to result in malformations, since all organs have been formed.

Note: No significant increase in probabilities below 100 mGy.
Source: Ebina, et al . (2012)

RADIODIAGNOSIS FOR PREGNANT PATIENTS
• It might be absolutely necessary to perform radiodiagnostic procedures on the pregnant
mother.
• The most common procedures by pregnant women are:
• X-ray pelvimetry (for detection of cephalopelvic disproportion).
• Chest Radiography (for preoperative evaluation)
• Diagnostic X-ray imaging for significant and urgent maternal or foetal medical problems
or trauma
• Radiation doses from most Radiodiagnosis present no substantial risk to foetus.
• Foetal doses of 100 mGy are NOT reached, even with 3 pelvic CT or 20 X-ray scans.

OPTIMIZATION IN RADIODIAGNOSIS
To keep the dose to foetus as low as reasonably achievable (ALARA), esp.
for cardiac catherization, it is recommended that:
• Lead barrier be wrapped around mother’s abdomen from diaphragm to
symphysis pubis.
• If possible, procedure should be performed after the period of major
organogenesis (>12 weeks). At 4th month, volume of foetus is small so that
there is great distance between foetus and chest.

APPROXIMATE FOETAL DOSES FROM PROCEDURES
METHOD PROTOCOL MEAN (mGy) MAX (mGy)
X-RAY
Skull or thoracic spine <0.01 <0.01
Chest <0.01 <0.01
Lumbar spine / Intravenous
Urogram
1.7 10
Abdomen 1.4 4.2
Pelvis 1.1 4
FLUOROSCOPY
Barium meal (UGI) 1.1 5.8
Barium enema 6.8 24
CT
Head CT <0.005 <0.005
Chest CT 0.06 1.0
Lumbar spine 2.4 8.6
Abdomen CT 8.0 49
Pelvis CT 25 80
NUCLEAR
MEDICINE
Tc – Bone 3.3 -
Tc – Brain 4.3 -
Sources: Health
Protection Agency
(2008);
J. Bushberg
(2002); S. Ebina
(2012)

TERMINATION OF PREGNANCY
• For foetal doses less than 100 mGy, there is NO MEDICAL
JUSTIFICATION for termination of pregnancy due to radiation risk.
• Even above 100 mGy, the decision to terminate should be based upon
individual circumsances – dose, stage of pregnancy, decision of parents.

MRI IN PREGNANCY
• Despite MRI being non-ionizing radiation, there is no conclusive
evidence to establish safety of MRI in pregnant women.
• The International Electrotechnical Commission (IEC 60601-2-33)
advises caution in imaging pregnant women with MRI.
• Recommendations in the UK advise not to scan in first trimester.
Ultrasound is considered safer whenever possible.
• More research is required.

OCCUPATIONAL EXPOSURE OF PREGNANT
EMPLOYEES
• 1 mSv foetal dose is the recommended set limit for whole period of the
pregnancy. This is approximately the same dose received by members of the
public.
• However, the USA set its own limits at 5 mSv foetal dose. Though, controls
must be implemented to ensure a significant fraction of the dose limit is NOT
imparted over a short period, e.g. 0.5 mSv /month max. or 1.5 mSv cumulative
for any 3 consecutive months.
• If necessary, for the duration of the pregnancy, the employee may be
redeployed to an area of lower radiation exposure.

OCCUPATIONAL EXPOSURE OF PREGNANT
EMPLOYEES
• TRICK QUESTION: True or False? Regarding dose limits, the annual dose
limit for the abdomen over the period of pregnancy for a pregnant employee working
with diagnostic X-rays is 1 mSv.
• Ans: FALSE. The occupational foetal dose limit is truly 1 mSv. Assume foetal dose is no
greater than 50% of dose on surface of abdomen of mother in diagnostic X-rays, thus the
dose limit for abdomen of worker should be 2 mSv max. (Source: S. Ilyas, 2011)
A TLD placed at the mother’s waist can estimate the abdomen surface dose, read out /
monitored every 1 -3 months.

NUCLEAR MEDICINE FOR PREGNANT PATIENTS
• Pregnancy is not an absolute contraindication.
• As a rule, a pregnant woman should not be subject to nuclear medicine
therapy with radioactive substance, unless it is life-saving.
• Some studies such as confirmation or exclusion of pulmonary embolus
require Nuclear Medicine.
(Research shows that risk of pulmonary embolus increases 7 folds immediately after
childbirth).

POTENTIAL SOURCES OF FOETAL DOSES IN NM
1. Doses to the conceptus or newborn from gamma-emitting
radionuclides in the mother's tissues.
2. Doses to the conceptus or newborn child from radionuclides
transferred to the offspring during pregnancy.
3. Doses to the newborn child from radionuclides in the mother's breast
milk.

NUCLEAR MEDICINE FOR PREGNANT PATIENTS (contd.)
• For optimization in pregnant patients, a smaller than normal activity of
radiopharm may be administered with longer imaging time.
• The urinary bladder is a major source of foetal irradiation.
• Maternal hydration and frequent urination should be encouraged.
• Pregnancy should be avoided after therapeutic treatment using radionuclides for a
period of time.
• Males treated with 131I, 32P or 89Sr should avoid fathering children for a period of 4
months after treatment. (4 months is about the average life of a sperm cell).

NUCLEAR MEDICINE FOR PREGNANT PATIENTS (contd.)
• 99mTc: Most diagnostic procedures with 99mTc do not cross the placenta. There is
minimal risk. The foetal dose is derived from radioactivity in maternal tissues (e.g.
Bladder). Tc-bone contributes 3.3 mSv foetal dose while Tc-brain contributes 4.3 mSv.
• Iodine Isotopes: Most cross the placenta and settle in a specific organ/tissue
(e.g. Thyroid), which can pose a significant risk to the foetus. Same with 32P.
• Therefore, treatment of hyperthyroidism can be delayed until after pregnancy, and
the patient in the interim can be treated with drugs.

NUCLEAR MEDICINE FOR BREASTFEEDING MOTHERS
• Many radionuclides may concentrate in breast milk.
• For some radionuclides, a total cessation of breastfeeding is required.
e.g. 131I–NaI, 125I-HSA, PSA).
• Others require a few hours of cessation – e.g. 123I-NaI (9 hr),
123I-MIBG (24 hr), 111In-WBC (48 hr), 201Tl-Chlorine (30 hr).
• For others, no action is required for others. Breastfeeding can continue.
e.g. 99mTc-DTPA, MDP.

INSTRUCTIONS FOR BREASTFEEDING MOTHERS IN NUCLEAR MEDICINE
Source: Nuclear Medicine
Resource Manual, IAEA,
2006.

DOSE COEFFICIENTS:
MEASURING FOETAL DOSE IN NUCLEAR MEDICINE
• There are ways of calculating the radiation dose to the foetus in NM, and tables of radiation
doses. These are Dose Coefficients (DC).
• ICRP 88 (2001) provides dose coefficients necessary for calculation of foetal dose.
e.g. A nuclear technologist who accidentally inhaled 1000 Bq during her
25th week of pregnancy.
Solution: Under DC, acute inhalation of elemental 131I vapour
during 25th week is listed as 3.1 x 10-8 Sv/Bq.
Thus, foetal dose = 3.1 * 10-8 * 1000 Bq = 31 μSv
If dosimeter reads 100 μSv (external dose),
Then total foetal dose = 31 + 100 = 131 μSv

NUCLEAR MEDICINE FOR PREGNANT WORKERS
• ICRP 84 suggests that a pregnant worker “can be restricted from
spending a lot of time at the radiopharmacy or working with solutions of
radioiodine”.
• Special monitoring should be provided for pregnant worker.

RADIOTHERAPY IN PREGNANCY
• Unless absolutely necessary, radiotherapy (XRT) should be avoided if
patient is pregnant.
• Termination of pregnancy, other methods of therapy (e.g. chemotherapy),
postponement of XRT are alternatives.
• Pregnant patients are rare in XRT (about 1 in 1000 patients). [AAPM].
• Approx. 4000 pregnant women per year in USA require XRT [Stovall, 1995]
• Most common indications are breast cancer, thyroid cancer and
cervical cancer.

RADIOTHERAPY IN PREGNANCY (contd.)
• Foetal dose depends on the proximity of the uterus to target volume.
• The dose results from a combination of head leakage, external scatter, and
scatter from patient’s own tissues.
• Foetal dose can be calculated from peripheral doses, as a function of field
size, beam energy, machine type, treatment volume and distance from field
edge.

RADIOTHERAPY IN PREGNANCY (contd.)
• According to the CDC, a foetal dose of 1 Gy will likely kill 50% of embryo. The dose
necessary to kill 100% of human embryos or foetuses before 18 weeks’ gestation is about 5 Gy.
• Proper shielding can reduce the dose to foetus by at least 50%.
• Treatment with XRT requires advanced consultation between the medical oncologist,
radiation oncologist, obstetrician and medical physicist.
• NCRP recommends that pregnant women should be treated with photons generated by
electrons < 10 MeV to optimize risk of neutron contamination.

XRT FOR CERVICAL CANCER IN PREGNANCY
• Most common indications for pregnant women requiring radiotherapy are:
breast cancer, thyroid cancer and cervical cancer.
• Radiotherapy for cervical cancer is pregnant patients is not practicable,
as there is no way to shield the conceptus from receiving an unacceptably high
dose.
• The conceptus will be enclosed in the primary radiation beam.
• Termination of pregnancy may be advised.

BREAST CANCER (AND THYROID CANCER) RADIOTHERAPY
• In these instance(s), the target volume is farther away from the foetal location.
• Radiotherapy can be done, but with careful planning and additional shielding.
• Fenig et al (2000) argued that for breast cancer, the dose received is unlikely to be
sufficient to cause an unacceptably high risk to the foetus; certainly not to the
extent of recommending abortion. (also Antypas et al, 1998; Greskovich and Macklis,
2000).
• The risk to foetus of radiation-induced cancer is about 15% for 1 Sv
(Mayles, et al., 2007).

CA BREAST XRT (contd.)
• The conceptus is NOT in the primary beam in breast XRT.
• The dose outside a beam is a function of:
 Distance from beam edge
 Changes with stage of pregnancy
 Field size
 As low as reasonably achievable
 Primary radiation energy
 NCRP recommends photons generated by electrons < 10 MeV to minimize risk

Fig: (a) Anterior and (b) lateral views of height of conceptus’ fundus at various times during pregnancy.

METHODS OF REDUCING FOETAL DOSE IN XRT
• 2 methods of reducing foetal dose:
A. Modifying treatment technique
B. Using lead shielding devices

A. MODIFYING TREATMENT TECHNIQUE
• Modify usual treatment technique by:
Changing field angles
Reduce field size
Choose different radiation energy
• The peripheral dose can be reduced further by treating the patient, so that the lower
collimator defines the field edge nearest the foetus.
• IMRT should be avoided because the contribution of head leakage will be
greater .
XRT IN PREGNANCY (contd.)

B. SHIELDING TECHNIQUES
• 3 major types of shielding arrangements:
Bridge over patient
Table over treatment couch
Mobile stands
XRT IN PREGNANCY (contd.)

Bridge Over Patient technique:
• Simplest shielding design
• Consists of bridge over patient’s
abdomen
• Bridge has 5-7cm of lead
(4-5HVLs of lead)
• Posterior fields are treated by
patient lying prone.
SHIELDING TECHNIQUES (contd.)
Table over Treatment Couch technique:
• A table that rests on the treatment
couch.
• Patient can remain in supine position
for ant., posterior and lateral fields.
• Weight of lead may require additional
support for treatment couch.
Mobile Shields
• Has own stand
• Advantage: Ease of
movement and positioning
• Disadv: Cost

STEPS FOR RADIOTHERAPY
FOR PREGNANT WOMEN
1. Complete normal treatment planning as though
patient is not pregnant.
2. Consider modifying treatment plan to reduce foetal
dose.
3. Estimate dose to foetus with special shielding using
out-of-beam data measured in phantom. Use 3 points
– fundus, umbilicus (midpoint), symphysis pubis.
4. Design special shielding if foetal dose exceeds
acceptable limits. Usually 4 -5 HVLs of lead are
appropriate. Fig: 3 points of dose estimation

STEPS FOR RADIOTHERAPY FOR PREGNANT WOMEN (contd.)
5. Measure dose to foetus using simulated treatment, with
shielding in place.
6. Document plan and discuss with all medical personnel.
7. Check all aspects of safety, including load/weight limits of
treatment couch.
8. Be present for initial patient setup and available for
consultation.
9. Monitor foetal dose throughout radiotherapy (possibly with a
TLD or suitable dosimeter). Monitor foetus size and location too.
10. Consider referring patient to another institution if lacking in
personnel or equipment.
Fig: Measurement of shielding
with phantom

MEASUREMENT OF FOETAL DOSE IN
RADIOTHERAPY
1. Measurements are taken at three points – fundus, midpoint and pubis.
2. TLDs are placed at the surface of the mother’s abdomen for estimation.
3. Dose can be estimated using PDD, estimated depth of conceptus from abdomen
surface, and energy of beam.
4. Before treatment, simulation is done in a phantom with and without special
shielding. The phantom should simulate full-scatter geometry.
5. The total dose outside a beam can be measured in a phantom (water, polystyrene,
or anthropomorphic) using an ionization chamber, diodes, or TLDs.

MEASUREMENT OF FOETAL DOSE IN XRT
(contd.)
No shielding required in this case for treatment of tibia (leg)

(contd.)
4.5cm lead blocks required in this case

(contd.)
7 cm lead blocks required in this case

FOETAL DOSE ESTIMATION
(RADIODIAGNOSIS AND NUCLEAR MEDICINE)
• Radiodiagnosis: TLDs or other dosimeters placed on the abdomen of the
mother will estimate the abdomen surface dose. The foetal dose is assumed to
be about 50% of that.
To minimize exposure (optimization), shielding should be used whenever
possible.
• Nuclear Medicine: Dose coefficients are used. Tables exist for this at
different radionuclides inhalation or ingestion at different gestation ages.
SUMMARY

FOETAL DOSE ESTIMATION
(IN ACCIDENTAL EXPOSURE)
• The dose to foetus is
assumed to be the effective
dose to the uterus. Which can
be calculated as a fraction 0.05
using tissue weighting factor.
• The remainder includes uterus, brain,
intestines, kidney, etc.

CONCLUSION
• For pregnant employees, 1 mSv total foetal dose throughout the pregnancy is advised.
• A pregnant woman can undergo certain radiodiagnostic, radiotherapy and nuclear medicine
procedures.
• It is necessary to ascertain if a woman is pregnant or likely to be pregnant in each case.
• Additional shielding and modification of techniques may be necessary.
• Cessation of certain activities by the mother (e.g. breastfeeding, intercourse) may be required
of the mother.
• Termination of pregnancy is not justified below 100 mSv foetal dose.

REFERENCES
A. D. Wrixon (2008). New Recommendations from the International Commission on Radiological Protection—a review. Vienna: Physics in Medicine and
Biology, Institute of Physics.
B. Jumah (1992). Radiation Exposure During Pregnancy. Africa Health. Online: www.ncbi.nlm.nih.gov/pubmed/12285082. Accessed August 10, 2017. Maryland:
PubMed.
C. Antypas, P. Sandilos, J. Kouvaris, et al. (1998) Fetal dose evaluation during breast cancer radiotherapy. Int J Radiat Oncol Biol Phys. 1998;40:995–999.
Centre for Disease Control and Prevention (2011). Prenatal Radiation Exposure: A Fact Sheet for Physicians.
D. R. Dance et al. (2014). Diagnostic Radiology Physics: A Handbook for Teachers and Students. Vienna: IAEA
H. Cember, T. E. Johnson (2009). Introduction to Health Physics. 4th ed. New York: McGraw-Hill
Health Protection Agency (2008). Guidance on the Application of Dose Coefficients for the Embryo, Fetus and Breastfed Infant in Dose Assessments for
Members of the Public.
J. F. Greskovich Jr, R. M. Macklis (2000) Radiation therapy in pregnancy: risk calculation and risk minimization. Semin Oncol 27:633, 2000.
J. T. Bushberg, et al. (2002). The Essential Physics of Medical Imaging. 2nd ed. Philadelphia: Lippincott Williams & Wilkins.
IAEA (2006). Nuclear Medicine Resources Manual. Vienna: International Atomic Energy Agency.
Medical Devices Agency (2002) Guidelines for Magnetic Resonance Diagnostic Equipment in Clinical Use. London: Medicines and Healthcare Products
Regulatory Agency.
M. Stovall (1995). AAPM Report 50. AAPM TG 36. Fetal dose from radiotherapy with photon beams: Report of AAPM Radiation Therapy Committee Task
Group No. 36
P. Mayles, A. Nahum, J. C. Rosenwald (2007). Handbook of Radiotherapy Physics: Theory and Practice. Florida: Taylor and Francis.
S. Ebina, Y. Mariya, I. Kashiwakura (2012). The Effects of Maternal Exposure to Radiation on the Fetus. Japan: Radiation Emergency Medicine Vol 1 No. 1-2 27-
32.
S. Ilyas et al. (2011). Physics MCQs for the Part 1 FRCR. Cambridge: Cambridge University Press.

THANK YOU
To contact the author, email:
ekpovictortoday@gmail.com

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