RADIATION EXPOSURE DURING PREGNANCY

4. Terminology: Radiation Dose and Exposure Radiation : Transport of energy through space. Radiation can be either particulate or electromagenetic. Electromagnetic radiation: Radiation that consists of a combined electric and magnetic field that travels through space as pure energy. Common examples are light, radio waves, microwaves, X-rays, and gamma rays.

5. contd Particulate radiation: Radiation in the form of particles having measurable mass. The particles may be electrically charged or they may be neutral. The most commonly encountered particulate radiations are the 3 atomic particles (neutrons, protons, and electrons) that have been liberated from their usual bonds.

6. Contd Radiation dose: A way of describing the amount of energy transferred into a material that has been exposed to radiation. The unit of radiation dose in the SI system (Ile Systeme International d'Unites) is the grey (Gy). In the older centimeter-gram-second (GCS) system, it was the rad.

7. Contd Gray (Gy): 1 Gy represents the absorption of 1 joule (J) of energy by 1 kg of any material, ie, 1 Gy = 1 J/kg. Rad (obsolete): 1 rad represents the absorption of 100 ergs of energy by 1 g of material; ie, 1 rad = 100 erg/g = 0.01 Gy; 100 mrad = 1 mGy.

8. Contd Sievert (Sv): The unit of radiation dose equivalent in the SI system. Rem (obsolete): The unit of dose equivalent in the CGS system (1 rem = 0.01 Sv; 1 mSv = 100 mrem). Radiation from x-ray and CT scan is measured in rad, rem, gray & sievert (1 rad = 1rem = .01gy = 0.01 Sv)

9. Biologic effects of Radiation Radiation must produce double - strand breaks in DNA to kill a cell Radiation can also produce effects indirectly by interacting with water to generate free radicals, which can damage the cell. Ionizing radiation + H2O ? H2O+ + e- H2O ? H3O+ + OH OH ? Cell damage

10. The biologic effects When cells divide, the damage is multiplied. That is why radiation exposure is a greater risk during preg, when fetal cells are developing and multiplying. In some cases, cells can repair themselves. When they cannot, there may be a higher risk of cancer or hereditary effects.

11. Exposure during pregnancy Exposure to substantial amounts of radiation during pregnancy may cause birth defects, miscarriage, mental retardation, decrease in IQ, a higher risk of childhood cancer higher risk of cancer in adult life, hereditary effects that can be passed on to future generations.

13. Irradiated in the G2 phase, chromatid aberations may result. The frequency of chromosomal aberrations in peripheral circulating lymphocytes correlates with the dose received. Lymphocyte analysis may provide evidence of recent total body exposure.

15. Stochastic Effects Radiation -induced damage that is incompletely or incorrectly repaired ?es the probability of genetic mutation in affected cells. Somatic type effects, cancer, appearing in irradiated people years or even decades after exposure. Reproductive type effects small probability of radiation - induced heritable genetic effects in the progeny of those exposed.

16. Carcinogenic Effect of Radiation Cancer’s induction and development follow multistage process influenced by many factors inside and outside the body. Radiation Exposure ? the cancer risk Radiation Exposure mutations induced in somatic cells alter cell proliferation benign or noncancerous tumors. Additional mutations in benign tumor may caused malignant changes.  

17. Effective Dose Some tissues and organs are more sensitive to radiation than others. When the entire body is irradiated uniformly, all organs receive a dose and contribute to the total risk of a health effect, such as cancer. Effective dose is expressed in sievert (Sv) when the absorbed dose is measured in Gy, or rem or rads; 1 Sv = 100 rem.

18. Dosimetry Dosimetry is the process of determining the effective ionizing radiation received by persons exposed. Once the fetal radiation dose is estimated, the potential health effects can be assessed required today for radiation workers also that might be exposed during routine occupational activities.

19. Prenatal radiation exposure Human embryo or fetus is protected in the uterus, a radiation dose to a fetus tends to be lower than its mother for most radiation exposure events. However the human embryo and fetus are particularly sensitive.

20. Contd: Fetal sensitivity depends on radiation dose and amount of time it was exposed, Dose needs to be estimated before potential health effects can be assessed. Babies who received a small dose of radiation (equal to 500 chest x-ray or less at any time during pregnancy do not have an increase risk for birth defect. Only increase risk of cancer later in life.

21. Contd.. If a pregnant woman ingests or inhales a radioactive substance absorbed in blood (or enters bloodstream through a contaminated wound), pass through the placenta to the fetus. Even though for some substances the placenta acts as a barrier to the fetal blood, most substances that reach the mother’s blood can be detected in the fetus’ blood, with concentrations that depend on the specific substance and the stage of fetal development.

22. Contd.. Few substances (such as iodine) needed for fetal growth and development can concentrate more in the fetus than in corresponding maternal tissue. Radioactive substances that may concentrate in the maternal tissues surrounding the uterus including the mother’s urinary bladder can irradiate the fetus. For substances that can localize in specific organs / tissues in the fetus, consideration of the dose to specific fetal organs may be prudent such as iodine-131 or iodine-123 in the thyroid, iron-59 in the liver, gallium-67 in the spleen, and strontium-90 and yttrium-90 in the skeleton,

25. Contd.. Acute dose: dose delivered in a short time. Fractionated or chronic doses: doses delivered over time. Fetal dose of 1 Gy (100 rads) - kill 50% of the embryos. 5 Gy (500 rads) dose - kill 100% of embryos or fetuses before 18 wks’ gestation For adults, the LD50/60 (the dose necessary to kill 50% of the exposed population in 60 days) is about 3-5 Gy (300-500 rads) and the LD100 (the dose necessary to kill 100% of the exposed population) is around 10 Gy (1000 rads)

26. Gestational age and radiation dose are important determinants of potential noncancer health effects. Before 2 wks gest - exposure of > 0.1 gray (Gy) or 10 rads - death of the embryo Embryo is made up of only a few cells. Damage to 1cell can cause the death. If the embryo survives, radiation-induced noncancer health effects are unlikely, no matter what the radiation dose, however, will exhibit few congenital abnormalities (brith defects).

27. Radiation-induced noncancer healthdepends on dose & gest. age No Risk - < 0.05 Gy (5 rads) Small, malformations, central nervous system - 0.05–0.10 Gy Congenital effects - 0.10–0.20 Gy (10–20 rads). 16 weeks’ gestation to birth, are unlikely below about 0.50 Gy (50 rads). Impaired brain function >0.10Gy (10 rads) The normal rate of failure of a blastocyst to implant in the uterine wall is high, perhaps 30%–50%. After the embryo implants there, however, the miscarriage rate decreases to about 15% for the rest of the pregnancy.

28. Contd: at 8–15 wks’ - Radiation affect brain development. The average IQ loss is app 25–31 points / Gy (per 100 rads) above 0.1 Gy (10 rads), and the risk for severe mental retardation is app 40% per Gy. 16 - 25-wk - CNS is less sensitive. Average IQ loss is app 13–21 points / Gy (per 100 rads) above 0.7 Gy (70 rads), and the risk for severe mental retardation is app 9% / Gy (per 100 rads) above 0.7 Gy (70 rads). Beyond 26 wks - the fetus is less sensitive exposure than in any other stage of gestation.