radiation risks from fetal exposure

medical exposure

the radiation dose to the embryo/fetus from diagnostic procedure should present no…

risk of fetal death, growth retardation, or impairment of mental development

• diagnostic procedures (fetal dose less than 1 mGy) the risk of childhood cancer is very low

• higher doses, such as those involved in therapeutic procedures can result in significant harm

occupational exposure

a pregnant worker can continue working with radiation as long as there is…

reasonable assurance that the fetal dose can be kept below 1 mGy during the pregnancy

accidental exposure in pregnancy

• where pregnancy is discovered after exposure, the dose to the fetus should be estimated by an appropriately qualified medical physicist

• the dose estimate is used to inform a discussion between patient and clinician to agree the medical management of the fetus and provision of counselling for the patient

• in some jurisdictions, there is a requirement to notify the relevant regulatory authority of significant accidental or unintended exposures in medicine

for planned exposures of the known pregnant patient

• patient may require radiological examinations or even radiotherapy while pregnant

• the most common reason for justified lifesaving imaging is trauma

other medical issues that occur with increased prevalence during pregnancy include

• pulmonary embolism

• renal obstruction from stones

• acute neurological conditions

CT abdomen/pelvis is used for….

evaluation of acute abdominal pain e.g. suspected appendicitis, stones, ovarian torsion, bowel obstruction

cardiac imaging is used for….

assessment of valve functions, implant screening, or cardiac catheterization

recent literature shows that, in general, fetal doses from interventional procedures to treat complications in pregnancy rarely exceed…

50 mGy

occupational exposures in pregnancy

once pregnancy has been declared:

• additional controls have to be considered to protect the unborn child

• working conditions

3 options for pregnant staff

1- no change in assigned working duties

2- change to another area where levels of radiation may be lower

3- change to a job that has essentially no radiation exposure

a developing embryo is extremely sensitive to radiation. as post conception time increases…

radiosensitivity decreases

response of the embryo/fetus to radiation depends on…

the dose

dose rate

quality of radiation

stage of fetal development

embryo/fetus is particularly at risk due to:

• the rapid division of cells

• their developing organs

• their long life expectancy

there are 3 kinds of effects from antenatal exposure:

1- lethality

2- congenital anomalies

3- large delay effects (cancer and hereditary effects)

there are radiation related risks throughout pregnancy which are related to:

1- the stage of pregnancy

2- absorbed dose

radiation risks are most significant during…

organogenesis and in early fetal period (somewhat less in 2nd trimester, least in the 3rd trimester)

stages of fetal radiation risk: pre-implant stage

• up to 10 days post conception, the embryo contains only a few cells which are not specialized

• if too many cells are damaged, the embryo is resorbed (lethal effect)

• if only a few cells are killed, the remaining cells replace those lost (within few cell divisions)

• the response is considered ‘all or nothing’ i.e. lethality or survival

• atomic bomb survivors had a high incidence of both normal birth and spontaneous abortion

stages of fetal radiation risk:

organogenesis

• 2nd - 8th week post conception

• malformations occur more frequently during this period of major organogenesis

• each organ system is not at equal risk during this period

• risk is greatest at the period of peak differentiation of each system

factors influencing malformations:

• radiation quantity and quality

• dose rate

• oxygen

• cell type and its relationship to surrounding tissues

stages of fetal radiation risk:

fetal growth stage (after organogenesis until term)

• during the fetal growth stage, the incidence of radiation induced prenatal death and congenital anomalies is, for the most part, negligible

• anomalies include those affecting the CNS and the sense organs

• damage induced during this fetal growth stage, which are seen in later life and include
  - behavioural alterations
  - reduced IQ

deterministic effects: central nervous system (CNS)

effects of CNS can occur during weeks 8-25 post-conception

CNS is particularly sensitive to radiation

development of the CNS is over a relatively long period

effects can include a reduction of IQ

a threshold dose is not apparent for these effects however below 100 mGy, effects are undetectable and not of practical significance. the exitance or otherwise of a threshold is currently a matter of debate

experimental & human data is in good agreement

deterministic effects: central nervous system

fetal doses in the region of 300 mGy can result in…

severe mental retardation (SMR)

deterministic effects: central nervous system

fetal doses in the region of 1000 mGy (1 Gy)

increase the risk of SMR to 40%

are associated with a decline in IQ of about 25 points/Gy particularly during 8-15 weeks and to a lesser extent at 16-25 weeks

stochastic effects: increased risk of cancer

radiation has been shown to increase the risk of leukemia and many types of cancer in adults in children. throughout most of the pregnancy, the embryo/fetus is considered to be…

at about the same risk for carcinogenic effects as children (i.e. a few times that of the populations as a whole)

stochastic effects: increased risk of cancer

following a fetal dose of [1], the relative risk may increase by [2] over normal incidence. the normal incidence of childhood cancer [3]

1- 10 mGy

2- 40%

3- 0.2-0.3%

individual risk, however, is small with the risk of cancer at ages 0-15 being about 1 excess cancer death per 1,700 children exposed in utero to 10 mGy

stochastic effects: genetic effects

the present estimate from the ICRP is about [1] than it had been in the past. radiation doses from exposure to diagnostic exams in pregnancy present a [2] of causing radiation induced hereditary disease in the descendants of the unborn child.

1- 5 times lower

2- negligible

risks in a pregnant population NOT exposed to medical radiation

termination of pregnancy for fetal doses of 100 mGy vs for fetal doses more than 100 mGy

• less than 100 mGy: termination is not justified based on radiation risk

• more than 100 mGy: there can be fetal damage, the magnitude and type of which is a function of dose and stage of pregnancy. high fetal doses (100-1000 mGy) in late pregnancy are not likely to result in malformations or birth defects because all organs have formed

pre-conception irradiation of either parent’s gonads…

has not been shown to result in increased cancer risk or malformations in children

types of fetal doses in radiology: diagnostic procedure

• radiation dose to embryo/fetus from diagnostic procedures should present no risk of fetal death, growth retardations or impairment of mental development

• for the majority of diagnostic procedures (fetal dose < mGy) the associated risk of childhood cancer is very low

• the natural risk of childhood cancer is approximately 1 in 500

types of fetal doses in radiology: therapeutic procedures

• higher doses, such as those involved in therapeutic procedures can, however, result in significant fetal harm

typical fetal doses and risks of childhood cancer for some common diagnostic medical exams (from hpa, uk, 2009)

typical fetal doses and risks of childhood cancer for some common diagnostic medical exams (from hpa, uk, 2009)