Chapter 37 Radiation and Pregnancy and Genetic Effects

1
Chapter 37 Radiation and Pregnancy and Genetic
Effects

• From the first medical application of x-rays,
  there has been a concern and apprehension
  regarding the effects of radiation before, during
  and after pregnancy.
• Before pregnancy- concerns about fertility
• During pregnancy- possible congenital effects
• After pregnancy genetic effects
• All have been observed in animals and humans.

2
Effects on Fertility

• The early effects of high level radiation
  exposure on fertility is known in both men and
  women.
• Doses as low as 10 rad may delay or suppress
  menstruation in women and reduce the number of
  spermatozoa.
• Doses of 200 rad can produce temporary
  infertility.
• Dose of 500 rad will produce sterility.

3
Effects on Fertility

• The short term effects are documented and known
  to be dose related.
• The effects of low-dose, long term irradiation on
  fertility is less well defined.
• Animal results are lacking. Those that exist
  demonstrate no effect in exposure of 100 rad per
  year.
• A study of 150,000 rad techs found no effect on
  fertility over a 12 year sampling period.
• Low-dose, chronic irradiation does not impair
  fertility.

4
Irradiation in Utero

• Irradiation in utero concerns two types of
  exposures.
• Those to the radiation worker
• Those to the patient
• There is substantial data about animal exposure
  to relatively high doses of radiation delivered
  during the various periods of gestation.

5
Irradiation in Utero

• The embryo is a rapidly developing cell system so
  it is very sensitive to radiation.
• With age, the radiosensitivity decreases and the
  pattern continues into adulthood.
• The effects of exposure in utero are time and
  dose related.

6
LD50/60 of mice

• After maturity, radiosensitivity increases with
  age.
• It begins to decrease with age at the end of
  child bearing age.
• The study shows mice age in weeks and human age
  in years.

7
Effects of 200 Rad Delivered at Various Times in
Utero
8
Exposure During the 1st Trimester

• All observations point to the first trimester of
  pregnancy as the most radiosensitive period.
• With in the first two weeks after fertilization
  to most pronounced effect of a high radiation
  dose is fetal death which is manifested as a
  spontaneous abortion.
• Observed in radiation therapy patients but only
  after very high exposures.
• The 1st 2 weeks of pregnancy may be of least
  concern because the response is all or nothing.

9
Exposure During the 1st Trimester

• From animal data, it would appear that this
  response is very rare. The best estimate is a 10
  rad exposure during the first two weeks would
  induce 0.1 rate of spontaneous abortion. This is
  added to the 25 to 50 normal incidence of
  spontaneous abortion.
• Fortunately there will either be a spontaneous
  abortion or the pregnancy will carry to full term
  with no effect.

10
Exposure During the 1st Trimester

• During the 2nd to 10th weeks two effects may
  occur.
• Early in this period, skeletal and organ
  abnormalities can be induced.
• As organs continue to develop, central nervous
  system abnormalities may develop.
• If the abnormalities are severe enough, the
  effect will be fetal death.
• After a dose of 200 rad, nearly 100 of the
  fetuses suffered significant abnormalities.
• In 80,it was sufficient to cause death.

11
Exposure During the 1st Trimester

• Such effects after diagnostic levels of exposure
  are essentially undetectable after radiation
  doses of less than 10 rad.
• A dose of 10 rad during organogenesis is expected
  to induce congenital abnormalities by 1 above
  natural occurrence.
• To complicate this there is a 5 incidence of
  naturally occurring congenital abnormalities in
  the unexposed population.

12
Exposure During the 1st Trimester

• In utero irradiation has been associated with
  childhood malignancy. Oxford University has
  studies every childhood malignancy in England,
  Scotland and Wales since 1946.
• They found that childhood leukemia was of
  particular importance. The relative risk was 1.5
  or an increase of 50 over the non-irradiated
  rate. The number is very small.

13
Relative risk of Childhood Leukemia after
Irradiation by Trimester

• Time of X-ray Exam
• First Trimester
• Second Trimester
• Third Trimester
• Total

• Relative risk
• 8.3
• 1.5
• 1.4
• 1.5

14
More Effects of in Utero Exposure

• Observed in Atomic Bomb survivors has been an
  increase in mental retardation. This involved
  very high exposure rates
• It is known that radiation does retard growth.
  Irradiation particularly during organogenesis has
  been associated with microcephaly (small head)
  and retardation.
• Human data from atom bomb survivors and residents
  of the Marshall Islands exposed to fall out from
  atom bomb tests demonstrated impaired growth in
  children.

15
Summary of effects after 10 Rad in Utero
Time of exposure Type of Response Natural Occurrence Radiation Response
0-2 week Spontaneous abortion 25 0.1
2-10 weeks Congenital abnormalities 5 1
2-15 weeks Mental retardation 6 0.5
0-9 months Malignant Disease 8/10,000 12/10,000
0-9 months Impaired growth and development 1 Nil
0-9 months Genetic mutation 10 Nil
16
Genetic Effects

• We have no data suggesting that radiation induced
  genetic effects in humans. There has been no
  observed radiation induced genetic effects in
  the atomic bomb survivor or Marshall Islanders.
  They are now in their third generation.
• We must therefore rely on work done on fruit
  flies and mice.

17
H.J. Muller work with Fruit Flies

• Nobel prize winning geneticist H.J. Muller
  irradiated mature fruit flies and then measured
  the frequency of lethal mutations.
• He used thousands of rad but the response was
  linear non-threshold.

18
H.J. Muller work with Fruit Flies

• It was the results of his work that in 1932 the
  National Council on Radiation Protection (NCRP)
  lowered the recommended dose limits for workers
  and acknowledged the existence of the linear
  non-threshold radiation effects.
• Since that time all radiation protection guides
  have assumed a linear non-threshold response.

19
Conclusions Regarding Radiation Genetics

• Radiation-induced mutations are usually harmful.
• Any dose of radiation, however small, to a germ
  cell results in some genetic risk.
• The frequency of radiation induced mutations is
  directly proportional to dose, so that a linear
  extrapolation of data from high exposures proves
  a valid estimate for low dose effects.

20
Conclusions Regarding Radiation Genetics

• The effect depends upon protraction and
  fractionation.
• For most of the preproductive life, the women is
  less sensitive to genetic effects of radiation
  than the man.
• Most radiation-induced effects are recessive.
  This requires the mutant gene to be present in
  both the male female to produce the trait. Such
  mutations may not be expressed for many
  generations.
• The frequency of radiation induced genetic
  mutations is extremely low. It is approximately
  10-17 mutations/rad/gene.

21
Conclusion for Diagnostic Exposures

• The incidence of radiation-induced genetic
  mutations from exposure levels in diagnostic
  radiology is zero.
• For nearly all diagnostic exposures, no action is
  required.
• Should a high exposure in excess of 10 rad, some
  protective action may be required.

22
Female Precautions

• The prefertilized egg, in its various stages
  exhibits a constant sensitivity to radiation.
• It has demonstrated the ability to repair genetic
  damage.
• If repairs occur, it is rapid and therefore a
  delay in procreation of only a few days may be
  prudent.

23
Male precautions

• In the male, it might be prudent to refrain from
  procreation for a period of 60 days to allow
  cells that were in a resistant stage of
  development at the time of exposure to mature to
  functioning spermatids

24
Summary

• The effects of low-dose, long term irradiation in
  utero can include
• Prenatal death
• Congenital abnormalities
• Malignancies
• Impairment of growth
• Mental retardation
• Genetic Effect

25
Summary

• These abnormalities are based upon exposure of
  more than 100 rad in humans and greater than 10
  rad in animal experiments.
• There is no evidence that diagnostic levels of
  radiation exposure currently experienced
  occupationally or medically are responsible for
  any such effects on fetal growth or development.

26
Chapter 38 Health Physics

• The term health physics was coined during the
  Manhattan Project as they developed the atomic
  bomb.
• A group of physicists and physicians were
  responsible for the radiation safety of personnel
  involved in the production of the atomic bombs.
• The health physicist is concerned with
• Research
• Teaching
• Operational aspects of radiation safety.

27
Health Physics

• Health physics is concerned with providing
  occupational radiation protection and minimizing
  radiation dose to the public.
• There are three cardinal principles developed for
  nuclear activities that have equally useful
  applications in diagnostic radiology.
• By observing these principles, radiation exposure
  can be minimized.

28
Cardinal Principles of Radiation Protection

1. Keep the time of exposure to radiation as short
   as possible.
2. Maintain a large distance as possible between the
   source of radiation and the exposed person.
3. Insert shielding material between the radiation
   source and the exposed person.

29
Minimize Time

• Exposure Exposure rate x exposure time
• During radiography the exposure time is reduced
  to reduce motion blur.
• During fluoroscopy exposure time is reduced to
  reduce patient and personnel exposure.
  Radiologists are trained to switch the exposure
  on and off rather than continuous on to lower
  exposure. Pulsed progressive fluoroscopy reduces
  patient exposure by a factor of 0.1 or less
• Fluoroscopy machine have a 5 minute reset timer.

30
Maximize Distance

• As the distance from the source of radiation
  increases, the radiation exposure rapidly
  decreases. inverse square law
• I1 D22
• ---- -------
• I2 D12
• The source of radiation can be a point source
  like the tube and an extended area source like
  the patient.
• If you are 5 times the source diameter from the
  sources, it can be treated as a point source.

31
Maximize Distance

• During radiography the operator should be
  completely within a shielded control booth.
• During stress radiography, the operator may need
  to manipulate the area being radiographed so they
  should be in a lead apron and lead gloves.
• They also should be as far away from the primary
  beam as possible.

32
Maximize Distance

• During normal radiography, only the patient
  should be in the room during exposures.
• During fluoroscopy, the operator and technologist
  are in the room during exposure.
• During fluoroscopy the technologist should be as
  far away from the patient as possible.

33
Maximize Distance

• The exposure rate can be computed using
  isoexposure line to determine the safest place to
  stand during an exam.

34
Maximize Shielding

• Positioning shielding between the radiation
  source and exposed persons greatly reduces the
  level of radiation exposure.
• Shielding in radiography is generally lead or
  concrete.
• The amount of shielding material needed can be
  estimated if we know the HVL Half Value Layer or
  Tenth Value Layer of the shielding material.

35
Maximize Shielding

• The HVL is the amount of material needed to
  reduce intensity by 50.
• The TVL is the amount of absorber needed to
  reduce intensity to 10 of the original value
• 1TVL 3.3 HVL

36
Approximate HVL TVL of Lead and Concrete at
Various Tube Potentials
Tube potential HVL Lead (mm) HVL Concrete (in) TVL Lead (mm) TVL Concrete (in)
60 kVp 0.11 0.25 0.34 0.87
80 kVp 0.19 0.42 0.64 1.4
100 kVp 0.24 0.60 0.80 2.0
125 kVp 0.27 0.76 0.90 2.5
37
Dose Limits

• A continuing effort of the health physicists is
  to describe and identify occupational dose
  limits.
• For years a Maximum Permissible Dose (MPD) was
  specified for radiation workers.
• The MPD was the dose of radiation that would be
  expected to produce no significant radiation
  effects.

38
Dose Limits

• At radiation levels below the MPD, no response
  should occur. Thats the problem with MPD.
• The response at or below the MPD is not zero
  because of the linear non-threshold radiation
  dose response.
• The MPD has been replaced by Dose Limits (DL).

39
Dose Limits

• The NCRP has assessed risks based upon the BEIR
  Committee and the National Safety Council.
• State and federal government agencies routinely
  adopt the recommended dose limits as law.
• They are developed for whole body and various
  organs and for various working conditions.

40
Radiation Dose Limits

• Particular care must be taken to make certain
  that no radiation worker receives a radiation
  dose in excess of the DL.
• The DL is specified for occupational exposures.
• It must not be confused with medical x-ray
  exposure as a patient they receive.
• Patient exposure is kelp as low as possible but
  there is no limit or DL for patients.

41
Radiation Dose Limits

• The DL of 50,000 mrem per week was established
  in 1902. Through the years there has been a
  downward revision to the dose limits.
• The early DL was based upon a known acute
  response level and presumed that a threshold dose
  existed.
• The NCRP limits established in 1987 is 50 mSv per
  year (5000 mrem) Cumulative 10 mSv x age
• The International Commission on Radiation
  Protection limits established in 1991 limits of
  20 mSv per year (2000 mrem)

42
Radiation Dose Limits

• Because the basis of the DL assumes a linear,
  nonthreshold response, all unnecessary radiation
  must be avoided.
• Occupational exposure is defined as dose
  equivalent in units of millisevert (millirem).
• DL are specified as Effective Dose (E)
• The effective dose concept accounts for different
  types of radiation with varying relative biologic
  effectiveness.
• Effective dose also considers the relative
  radiosensitivity of various tissue and organs.

43
Radiation Dose Limits

• The effective dose concept is very important
  consideration when protective apparel such as
  lead aprons are used.
• Wearing an apron effectively reduces the
  radiation dose to many tissue types and organs to
  nearly zero.
• Therefore the effective dose is much less than
  the dose measured at collar level with a film
  badge.

44
Effective Dose

• Effective dose (E) radiation weighting factor
  (Wr) times Tissue weighting factor (Wt) time the
  Absorbed dose.
• For medical radiation uses, the radiation weight
  factor is 1. For other type of radiation it is
  based upon the LET of the radiation.
• The tissue weighting factor ranges from 0.20 for
  gonads (most radiosensitive) to 0.01 for skin
  (less radiosensitive).

45
Dose Limits for Tissues and Organs

• The whole body DL of 50mSv/year is an effective
  dose which take into account the weighted
  average of various tissue types and organs.
• Skin Some organs have a higher DL than the whole
  body DL. The DL for skin is 500 mSv/year.
• Eyes The DL for eyes is 15mSv/year.

46
Public Exposure

• Individuals in the general population are limited
  to 5mSv/year(500 mrem/year) if the exposure is
  infrequent. If the exposure is frequent as with a
  hospital employee who may visit radiology, the
  limit is 1 mSv/year (100 mrem/year).
• The 1mSv/year DL is what physicist use to compute
  thickness of protective barriers.

47
Educational Considerations

• Student under the age of 18 may not receive more
  than 1 mSv/year during their course of
  educational activities.
• For this reason, student technologists under 18
  may be engaged in x-ray imaging but their
  exposure is limited to 1mSv/year.
• It is a general practice to not accept underage
  students for RT programs.

48
ALARA Considerations

• ALARA stands for As Low As Reasonably Achievable
  and is the corner stone of radiation safety
  policies and procedures.
• The 1991 ICRP recommendation of reducing annual
  exposures to 20mSv per year is under review by
  the NCRP.

49
DLs, X-rays and Pregnancy

• Two situations in diagnostic radiology require
  particular care and action. Both are associated
  with pregnancy. Their importance is obvious from
  both a physical and emotional stand point.
• The severity of potential response to radiation
  in utero is both time and dose related.

50
X-rays during the first two weeks of pregnancy.

• A grave misconception is that the most critical
  time for irradiation is during the first two
  weeks of pregnancy when it is unlikely that the
  mother knows that she is pregnant. If fact this
  time during pregnancy is the least hazardous.
• The most likely biologic response to irradiation
  during the first two weeks is resorption of the
  embryo and therefore no pregnancy.
• There is a concern about possibility of inducing
  congenital abnormalities during this time but it
  has not been demonstrated in animals or humans at
  any level of radiation exposure.

51
Organogenesis

• During the 2nd through 10th weeks, major organ
  development is happening.
• If the exposure is significant, congenital
  abnormalities may result.
• Early responses may be skeletal deformities.
• Later responses may be neurological deficiencies.

52
2nd and 3rd trimesters

• During the later trimesters previously mentioned
  responses are unlike to occur.
• The results from numerous investigations strongly
  suggest that if a response occurs after
  diagnostic irradiation, the principle response
  would be the appearance of malignant disease
  during childhood.
• The dose limit for any response is 25 rad (250
  mGy).

53
2nd and 3rd trimesters

• This exposure level highly unlikely but is
  possible for patient receiving multiple
  examination of the abdomen or pelvis.
• Occupationally this exposure is impossible
  because the DL is so low.

54
Dose Dependence

• Virtually no information is available at the
  human level to construct dose-response
  relationships for irradiation in utero. Most
  estimates are extrapolation of data from a rat
  and mice.
• After a radiation dose of 200 rad, it is nearly
  certain that each of the previously discussed
  responses will occur. It is very unlikely that
  such an exposure of this magnitude would happen
  during diagnostic radiology.

55
Dose Dependence

• Spontaneous abortion is unlikely at exposure
  levels less than 25 rad. The precise nature of
  the dose-response is unknown but a reason able
  estimate of risks suggest that 0.1 of all
  conceptions would be resorbed after and exposure
  of 10 rad.
• The response for lower exposures would be
  proportionally lower. The risk of spontaneous
  abortion with no radiation is 25 to 50.

56
Radiation Induced Childhood Malignancy

• The induction of childhood malignancy after
  irradiation in utero is hard to assess. Risks are
  lower than those of a spontaneous abortion and
  congenital abnormalities. A best approach is to
  use a relative risk estimate.
• 1st trimester relative risk is 5 to 10. It drops
  to about 1.4 during the 3rd trimester. The
  overall relative risk is 1.5, a 50 increase over
  the naturally occurring incidence.

57
Pregnant Radiographer

• A radiologic technologist or operator should
  immediately notify their supervisor should they
  become pregnant.
• Once the supervisor is notified, they become
  declared and the DL becomes 0.5 mSv/month (50
  mrem/mo).
• The DL for the fetus is 5 mSv (500 mrem) for the
  pregnancy.

58
Pregnant Radiographer

• In x-ray departments with fluoroscopy, everyone
  wears a personnel monitoring device at collar
  level. This records the radiation exposure
  outside the lead apron.
• For pregnant workers a second device is added and
  worn at waist level. It would be under the lead
  apron to record the fetal dose.

59
Pregnant Radiographer

• Usually the exposure under the apron would be
  less than 10 of the exposure at collar level.
• It is important to not get the two badges mixed
  up.
• Wrap around aprons are preferred during
  pregnancy. Apron should not extend below knees
  due to weight.

60
Pregnant Radiographer

• Using standard protective procedures, the
  radiographer and baby should not exceed or even
  come close to the DL.
• The radiology supervisor or director must
  incorporate three steps in the radiation
  protection plan.
• New employee training
• Periodic in service education
• Pregnancy Counseling

61
New Employee Training

• At the time of hire as part of orientation, the
  new employee should receive training in the
  protocols to follow in the even of pregnancy and
  their responsibility.
• Each employee should be provided with a copy of
  the departmental radiation protection manual.
  This might include a one page summary of dose
  limits, responses and proper radiation control
  procedures.

62
New Employee Training

• The new employee should read and sign a form
  indicating that she has been instructed in the
  area of radiation protection.
• An important point to be made is that the
  employee will voluntarily notify their supervisor
  if they become pregnant or might be pregnant.

63
In-service Training

• Most well run offices or departments will have a
  regular scheduled in-service education, usually
  on a monthly basis.
• At least twice annually, the subject should be
  radiation protection and control procedures.
• A review of personnel monitoring records is
  particularly important. Posting exposure reports
  for all to see is useful in showing that the
  occupational dose is well below the DL. Annually
  the employees should initial the report to
  document their review of their exposure.

64
Counseling During Pregnancy

• The director should counsel the employee at the
  time that they report that they are pregnant.
  This should include
• Review of their exposure history and any
  modification to their work schedule that are
  appropriate.
• Those who work heavily in fluoroscopy may exceed
  the 5 mSv exposure per year but this level of
  exposure is for the fetus. The fetal dose is
  measured with a second monitor worn at waist
  level under the apron.
• They should point out that alteration to the work
  schedule is usually not required in diagnostic
  radiology.

65
Counseling During Pregnancy

• The level of exposure of 5 mSv during gestation
  is considered as absolutely safe.
• Other radiation workers such as nuclear medicine,
  oncology technologist or sonographers have the
  same dose limits but different risks that may
  require a modification to their work habits.
  Under no circumstance should the employee be
  terminated or placed on an involuntary LOA.
• At the end, the employee is required to read and
  sign a document attesting the fact that she
  understands that the level of risks associated
  with her employment is less than that experienced
  by nearly all occupational groups.
• The recommended form is in the text.

66
The Pregnant Patient

• Safeguards against accidental irradiation early
  in pregnancy present complex administrative
  problem.
• The patient may not know that they are pregnant.
  Usually after the first two months, pregnancy is
  known.
• There are circumstances that the examination
  should not be performed.
• Strict compliance with protection procedures is
  important if the exam must be performed.

67
The Pregnant Patient

• One should never knowingly examine a pregnant
  patient with x-rays unless a documented decision
  to do so is made.
• Discuss the need for the exam with a radiologist
  before taking films.
• Should radiography be anticipated, determine the
  patients menstrual cycle and withhold the exam
  until any question about pregnancy is answered.

68
The Pregnant Patient

• Administrative approaches
• Elective booking or scheduling of x-rays around
  the menstrual cycle is the most direct approach.
  This may require office staff to be trained to
  ask about pregnancy or LMP.
• Posting of warning signs to alert the patient of
  potential hazard is the simplest.
• Patient questionnaire. The patient is required to
  determine their menstrual cycle

69
Patient Questionnaire

• This may be as simple as a question about the
  date of onset of menses and that they are not
  pregnant.
• The ten day rule can be a guide. We want to take
  the film before ovulation. The safest time should
  be between 10 and 14 days after the onset of the
  last menses or LMP.

70
Patient Questionnaire

• In many x-ray department, the patient is required
  to complete and sign a consent form before
  x-rays. The patient should be informed of the
  potential risks associated with x-ray examination
  of the abdomen or lumbar spine if they are
  pregnant.
• The patient can then make an informed consent to
  the exam.
• A sample form is in the text.

71
Accidents

• It has been estimated that fewer than 1 of all
  women referred for x-ray examinations are
  potentially pregnant.
• If the pregnant patient escapes detection and is
  irradiated there are responsibilities for the
  radiology service for the patent.
• Accident do happen.

72
Responsibilities to the patient

• Estimate the fetal dose.
• Consult a radiologist or health physicist.
• Use the type of examination, mAs, kVp and
  shielding used during the exam.
• Determine if the exposure exceed 1 rad more
  complex dosimetric evaluation should be
  conducted.
• The health physicist can make accurate fetal dose
  estimates.

73
Responsibilities to the patient

• Determine stage of gestation that the exposure
  happened.
• This can be done by the radiologist and referring
  doctor.
• Determine which alternative to recommend to the
  patient.
• Continue to term
• Terminate the pregnancy.

74
Responsibilities to the patient

• Continue to term
• Rarely would an abortion be indicated from
  diagnostic x-ray exposure. Because the natural
  incidence of congenital abnormalities is about
  5, no such event can be reasonably considered
  from diagnostic exposure.
• Damage to the fetus is unlikely below 25 rad
  fetal exposure though some suggest that lower
  exposure may cause mental developmental
  abnormalities.

75
Responsibilities to the patient

• Therapeutic Abortion
• Below 10 rad, exposure a therapeutic abortion is
  not indicated unless there are other risk factors
  involved.
• Above 25 rad, the risks of latent injury may
  justify termination of the pregnancy.
• Between 10 and 25 rad, the precise time of
  irradiation, the emotional state of the patient,
  the effect an additional child would have on the
  family and other social and economic factors must
  be carefully considered.

76
Responsibilities to the patient

• Fortunately experience with such situations has
  shown that fetal doses are consistently low. The
  fetal dose would rarely exceed 5 rad after a
  series of x-ray examinations.

77
Representative ESE and Fetal Doses from X-ray
Views with 400 Speed Receptor and High Frequency
Generators

• Examination
• C-spine AP
• Chest
• Thoracic spine AP
• Lumbopelvic AP
• Abdomen
• Wrist or Foot

• ESE (mr) Fetal dose (mrad)
• 110 0
• 10 0
• 180 1
• 250 80
• 220 70
• 5 0

78
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