1) Radiation exposure during weeks 8-15 of pregnancy poses the highest risk of detrimental effects like mental retardation and congenital abnormalities for the unborn child. Doses higher than 1Sv can cause abnormalities or death, while much lower doses may cause mental retardation. 2) The pre-implantation and organogenesis stages (weeks 2-9) are the most radiosensitive periods, as radiation exposure can cause embryonic or fetal death. During organogenesis, abnormalities are also more likely. 3) During the fetal growth stage, risks include mental retardation, diminished IQ, and increased risk of cancer induction depending on the trimester of exposure. Threshold doses exist for deterministic effects while stochastic effects like cancer have no

1. Radiation Protection Course For Radiologists
Lecture 4 of 8
Radiation Effects on Embryonic Development
And Foetal Life
Prof Amin E AAmin
Dean of the Higher Institute of Optics Technology
&
Prof of Medical Physics
Radiation Oncology Department
Faculty of Medicine, Ain Shams University

2. Deterministic Effects On The
Unborn Children I
❖ Non-stochastic effects may occur on the unborn child if the
mother is exposed to radiation.
❖ Radiation doses higher than 1Sv delivered during the period
of 2 to 9 weeks of pregnancy may produce congenital
abnormalities and sometimes death.
❖ Much lower doses can cause mental retardation.
❖ The highest risk is between 8 and 15 weeks after conception.

3. Deterministiceffects On The
Unborn Children II
❖ Radiation exposure during that critical period causes a
downward shift in the distribution of IQ.
❖ The probability of occurrence of mental retardation is about
40% per Sv.
❖ The probability of severe mental retardation increases with
dose.
❖ The effect is presumed to be deterministic with a threshold
related to the minimum shift in the IQ that can be
recognised.

4. Classical Triad Of Effects Of
Radiation On The Embryo
• Growth retardation
• Embryonic, fetal or neonatal death
• Congenital malformation

5. Age Minimal dose (Gy) for:
(weeks) Lethality Gross malformation
0-1 No threshold at day 1? No threshold at day 1? Mental retardation
0.1 thereafter
2-5 0.25 - 0.5 0.2 No effects observed to
5-7 0.5 0.5 about 8 weeks
7-21 > 0.5 Very few observed
Weeks 8-15: no
threshold?
To term > 1.0 Very few observed Weeks 16-25: threshold
dose 0.6 - 0.7 Gy
Deterministic Effects to Fetus

6. Incidence Of Prenatal & Neonatal Death
And Abnormalities
• As post-conception time increases RS decreases
• It is not easy to establish a cause-effect relation because there are a lot of
teratogenic agents, effects are unspecific and not unique to radiation.
• There are 3 kinds of effects: lethality, congenital anomalies and large
delay effects (cancer and hereditary effects).
Time
%
Pre-implantation Organogenesis Foetus
Lethality
Congenital anomalies

7. Incidence Of Prenatal & Neonatal Death
And Abnormalities
• Lethal effects can be induced by relatively small doses (such as 0.1
Gy) before or immediately after implantation of the embryo into the
uterine wall.
• They may also be induced after higher doses during all the stages
during intra-uterine development.
Time
%
Pre-implantation Organogenesis Foetus
Lethality
0.1 Gy

8. Incidence Of Prenatal & Neonatal Death
And Abnormalities
• Mental retardation:
• ICRP establishes that mental retardation can be induced by
radiation (Intelligence Quotient score < 100).
• It occurs during the most RS period: 8-25 week of pregnancy.
• Risks of antenatal exposure related to mental retardation are:
8-15 week 15-25 week
Severe mental retardation with
a risk factor of
0.4/Sv
Severe mental retardation with
a risk factor of
0.1/Sv

9. Factors Affecting Radiation Induced
Abnormalities On The Embryo
Radiation dose
Dose-rate
Type of cell population irradiated
Stage of gestation

10. Embryonic And Fetal Risks
•0 to 9 daysPreimplantation
•10 days to 6
weeks
Organogenesis
•6 weeks to termFetal

11. Pre Implantation Stage
❖Stage
➢From time of fertilization to morula implantation in post. Uterine wall.
❖Duration
➢8 – 10 days.
❖Radiosensitivity
➢Embryonic cells have high rates of cell division and cell differentiation.
➢ It is composed of relatively few cells.
➢It has very high radiosensitivity.
➢The probability of death is very high.

12. Pre-implant Stage (Up To 10 Days)
Only lethal effect, all or none
Embryo contains only few cells which are not specialized
If too many cell are damaged-embryo is resorbed
If only few killed-remaining pluripotent cells replace the
cells loss within few cell divisions
Atomic Bomb survivors - high incidence of both - normal
birth and spontaneous abortion

13. Radiation Hazards During Pre
Implantation Stage
❖Cell Death
❖Cell injury to morula leading to preventing further division and
accordingly abortion.
❖Severe malformations leading to incomplete life, then abortion.

14. 10 Day Rule
❖ It must be emphasized that both the ICRP and NCRP
recommended application of the 10-day rule only to those
studies that do not contribute to management of current disease.
❖ It, therefore, follows that studies which do contribute to
diagnosis or treatment of current disease should be performed
in fertile women without regard to stage of the menstrual cycle.
❖ The ACR supports the American College of Obstetricians and
Gynecologists’ 1977 Guidelines for Diagnostic X-ray
Examinations of Fertile Women.

15. NCRP Report 54, Page 6
Animal experiments have shown that irradiation during the pre-
implantation period generally produces an all-or-none effect, i.e.,
either very early embryonic death (pre- or immediately post-
implantation) is caused, or there is apparent normalcy (including
growth rate, fertility, and longevity) of survivors.

16. Sensitivity Of The Early Conceptus
• Till early 1980’s, early conceptus was considered to be very
sensitive to radiation - although no one knew how sensitive?
• Realization that:
– organogenesis starts 3-5 weeks after conception
– In the period before organogenesis high radiation exposure may lead
to failure to implant. Low dose may not have any observable effect.

17. Effects Of Radiation According To
Gestational Stage
Organogenesis: 7-13 weeks
– Embryo sensitive to lethal, teratogenic and growth-retarding
effects because of the criticality of cellular activities and the
high proportion of radiosensitive cells.
–IUGR, gross congenital malformations, microcephaly and
mental retardation are the predominant effects for doses > 50
rads
–There is no report of external irradiation inducing morphologic
malformation in humans unless the individual also had growth
retardation or a CNS anomaly

18. Radiation Hazards during
Implantation & Organogenesis Stage
❖Cell Death but with lower incidence.
❖Higher incidence of malformation.
❖Higher incidence of congenital malformations especially organs
formed during this stage, mainly;
➢Brain, spinal cord, n cells and sensation organs (ear, nose and eye).
➢Skeleton especially pelvic and thoracic cage malformations.
➢Muscular system.

19. Foetal Growth Stage
❖Stage
➢From end of organogenesis to birth.
❖Duration
➢180-200 days (6 months).

20. Fetal Radiation Risk
• There are radiation-related risks throughout pregnancy which are
related to the stage of pregnancy and absorbed dose
• Radiation risks are most significant during organogenesis and in
the early fetal period somewhat less in the 2nd trimester and least
in the third trimester
Less Least
Most
risk

21. Age Threshold for lethal
effects (mGy)
Threshold for
malformations (mGy)
1 day 100 No effect
14 days 250 -
18 days 500 250
20 days >500 250
50 days >1000 500
50 days to birth >1000 >500
Effects on Embryo and Fetus
Estimated threshold doses. Data are primarily based on
animal experiments

22. Radiation Effects On The Fetus
• Radiation effects during the period of foetal growth can be
categorized into three main parts.
Foetal Growth
period
1st Part
4-5 M
2nd Part
6-7 M
3rt Part
8-9 M

23. Radiation Effects On The Fetus
• Radiation effects during the 1st part of the period of foetal
growth (4th and 5th months) are similar to the effect during the
organogenesis period.

24. Radiation Effects On The Fetus
• Radiation effects during the 2nd part the period of
foetal growth (6th and 7th months) are;
– Mental retardation
– Diminution IQ
– Microcephaly
– Abnormal behaviour
– Cancer Induction

25. Radiation Effects On The Fetus
• Radiation effects during the 3rd part the period of foetal growth
(8th and 9th months) are similar to the effect on neonatal and
infancy life (1st 6 months).

26. Radiation-Induced Malformations
• Malformations have a threshold of 100-200 mGy or higher
and are typically associated with central nervous system
problems
• Fetal doses of 100 mGy are not reached even with 3 pelvic
CT scans or 20 conventional diagnostic x-ray examinations
• These levels can be reached with fluoroscopically guided
interventional procedures of the pelvis and with radiotherapy

27. Central Nervous System Effects
• During 8-25 weeks post-conception the CNS is particularly
sensitive to radiation
• Fetal doses in excess of 100 mGy can result in some
reduction of IQ (intelligence quotient)
• Fetal doses in the range of 1000 mGy can result in severe
mental retardation particularly during 8-15 weeks and to a
lesser extent at 16-25 weeks

28. Radiation Risks –Embryo And Fetus
Threshold dose
deterministic effects
Mental retardation
Cancer and leukemia
before 10 y of age
lifetime
Hereditary effects
50-100 mSv
40% / Sv
2% / Sv
15% / Sv
1% / Sv

29. Radiation Risks Embryo and Fetus
This figure can be used in a discussion of national
policies regarding termination of pregnancy due to
medical exposure.
Dose
(mGy)
Lethal effects
malformations
Mental
retardation
Cancer &
leukemia
before 10 years
Cancer &
leukemia
whole life
1 none ->1*10-4 4*10-4 5*10-5 1.5*10-4
10 none ->1*10-3 4*10-3 5*10-4 1.5*10-3
50 none ->5*10-3 2*10-2 2.5*10-3 7.5*10-3
100 none ->1*10-2 4*10-2 5*10-3 1.5*10-2

30. Risks In A Pregnant Population Not
Exposed To Medical Radiation
– Spontaneous abortion > 15%
– incidence of genetic abnormalities 4-10%
– intrauterine growth retardation 4%
– incidence of major malformation 2-4%

31. Doses And Risks For In Utero
Radiodiagnostics
Exposure Mean fetal dose
(mGy)
Hered. Disease Fatal cancer
to age 14 y
X-ray
Abdomen
Barium enema
Barium meal
IV urography
Lumbar spine
Pelvis
Computed tomography
Abdomen
Lumbar spine
Pelvis
Nuclear medicine
Tc bone scan
Tc brain scan
2.6
16
2.8
3.2
3.2
1.7
8
2.4
2.5
3.3
4.3
6.2 10-5
3.9 10-4
6.7 10-5
7.7 10-5
7.6 10-5
4.0 10-5
1.9 10-4
1.9 10-4
6.1 10-4
7.9 10-4
1.0 10-5
7.7 10-5
4.8 10-4
8.4 10-5
9.6 10-5
9.5 10-5
5.1 10-5
2.4 10-4
7.1 10-5
7.7 10-4
1.0 10-4
1.3 10-4

32. Comment On Fetus/Embryo
• Fetus/embryo is more sensitive to ionizing radiation than the
adult human
• Increased incidence of spontaneous abortion a few days after
conception
• Increased incidence
– Mental retardation
– Microcephaly (small head size) especially 8-15 weeks after conception
– Malformations: skeletal, stunted growth, genital
• Higher risk of cancer (esp. leukemia)
– Both in childhood and later life

33. Considerations For Pregnancy
Termination
• Normal rate of preclinical loss - > 30%.
• At 0.1 Gy (10 rads), this is increased by 0.1-1%.
• Consider the lifetime risk factor for induction of childhood
tumors to be 1 in 2000 per rad. At 5 rads, maximal risk for
childhood leukemia is 1 in 400. Conversely, probability of not
having childhood cancer is > 99%.
• If the fetal absorbed dose > 50 rads in the 7-13 week window,
there is a substantial risk of IUGR and CNS damage.

34. If A Pregnant Patient Must Be X-Rayed
• Tight collimation
• High kvp
• Shielding
• Reduced number of images
• Make sure to check with your supervisor and be aware of the
site’s protocol