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Chapter 37 Radiation and Pregnancy and Genetic Effects

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Title: 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
End of Lecture
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