Effects of Radiation on Life

Acute Radiation Damage

Acute radiation syndrome or damage describes health effects present within 24 hours of exposure to high amounts of ionizing radiation.

Learning Objectives

Recall the cause, symptoms of, and treatment for acute radiation poisoning

Key Takeaways

Key Points

  • Radiation sickness is caused by exposure to a large dose of ionizing radiation over a short period of time.
  • Relatively smaller doses of radiation result in gastrointestinal effects, while larger doses can result in neurological effects and rapid death.
  • Treatment of acute radiation syndrome is generally supported with blood transfusions and antibiotics.

Key Terms

  • ionizing radiation: High-energy radiation that is capable of causing ionization in substances through which it passes; also includes high-energy particles.

Acute radiation syndrome, also known as radiation poisoning, radiation sickness, or radiation toxicity, is a constellation of health effects that are present within 24 hours of exposure to high amounts of ionizing radiation, which can last for several months. The term acute refers to immediate medical problems rather than ones that develop after a prolonged period.

Radiation sickness is caused by exposure to a large dose of ionizing radiation over a short period of time, typically greater than about 0.1 Gy/h. This might be the result of a nuclear explosion, a criticality accident, a radiotherapy accident, escape of radioactive waste, human error in a nuclear reactor, etc.

image

A survivor of acute radiation syndrome: A photograph of an 11-year-old girl, who was 2 kilometers away from the Hiroshima bombing site, recovering from acute radiation syndrome.

Radiation Symptoms

The onset and type of symptoms depends on the radiation exposure. Relatively smaller doses result in gastrointestinal effects, such as nausea and vomiting, and symptoms related to falling blood counts, such as infection and bleeding. Relatively larger doses can result in neurological effects and rapid death. Treatment of acute radiation syndrome is generally supportive with blood transfusions and antibiotics.

Similar symptoms may appear months to years after exposure as chronic radiation syndrome when the dose rate is too low to cause the acute form. Radiation exposure can also increase the probability of developing some other diseases, mainly different types of cancers. These diseases are sometimes referred to as radiation sickness, but they are never included in the term acute radiation syndrome.

Classically, acute radiation syndrome is divided into three main presentations: hematopoietic (affecting the bone marrow), gastrointestinal (following radiation exposure to the stomach and intestines), and neurological/vascular (after exposure to the brain). The speed of onset of symptoms is related to radiation exposure, with greater doses resulting in a shorter delay in symptom onset.

The best prevention for radiation sickness is to minimize the exposure dose or to reduce the dose rate.

Increased Cancer Risk from Radiation

Up to 10 percent of invasive cancers are related to radiation exposure, including both ionizing radiation and non-ionizing radiation.

Learning Objectives

Recognize the relationship between radiation exposure and one’s chance of acquiring cancer

Key Takeaways

Key Points

  • Exposure to ionizing radiation is known to increase the future incidence of cancer, particularly leukemia.
  • Incorrectly repairing damage due to radiation exposure can result in morphological changes to the cell, acquisition of cellular immortality, and adaptations that favor tumor formation.
  • Decades may elapse between radiation exposure and the detection of cancer.

Key Terms

  • sievert: The amount of 1 joule of radiation energy deposited in 1 kilogram of human tissue.
  • melanoma: A dark-pigmented, usually malignant tumor arising from a melanocyte and occurring most commonly in the skin.
  • ionizing radiation: High-energy radiation that is capable of causing ionization in substances through which it passes; also includes high-energy particles.

Up to 10 percent of invasive cancers are related to radiation exposure, including both ionizing radiation and non-ionizing radiation. Additionally, the vast majority of non-invasive cancers are non-melanoma skin cancers caused by non-ionizing ultraviolet radiation.

Exposure to ionizing radiation is known to increase the future incidence of cancer, particularly leukemia. This association is based largely on studies of Japanese atomic bomb survivors. The relationship between cancer risk and radiation dose for that group was shown to be directly proportional.

image

Cancer risk by radiation dose: An increased risk of cancer has been shown to correlate with radiation dose. One example of this connection is shown here for Japanese survivors of the atomic bomb.

The mechanism by which this occurs is well understood, but quantitative models that aim to predict the level of risk remain controversial. The most widely accepted model posits that the incidence of cancer due to ionizing radiation increases linearly with effective radiation dose at a rate of 5.5 percent per sievert. If the linear model is correct, natural background radiation is the most hazardous source of radiation to the general public health, followed closely by medical imaging. Cancer is a stochastic effect of radiation, meaning that the probability of occurrence increases with effective radiation dose, but the severity of the cancer is independent of dose.

Cancer starts with a single cell whose operation is disrupted. Direct and indirect damage eventually impact chromosomes and epigenetic factors that control the gene expression. Cellular mechanisms will repair some of this damage, but some of these repairs will be incorrect, and chromosomal abnormalities will turn out to be irreversible. The development of cancer can be divided into three major stages: morphological changes to the cell, acquisition of cellular immortality, and adaptations that favor tumor formation.

Decades may elapse between radiation exposure and detection of cancer.

Genetic Defects from Radiation

Ionizing radiation from fallout can cause genetic effects, birth defects, cancer, cataracts, and other organ and tissue defects.

Learning Objectives

Recognize the name of the genetic defect that has been shown to be caused by acute radiation exposure during pregnancy

Key Takeaways

Key Points

  • By directly or indirectly ionizing, radiation can cause changes in a cell’s ability to conduct repair and reproduction.
  • Exposure to even relatively low doses of radiation has been shown to generate genetic damage in the progeny of irradiated rodents.
  • In humans, microcephaly is the only proven malformation, or congenital abnormality, found in the developing human fetuses present during the Hiroshima and Nagasaki bombings.

Key Terms

  • congenital: Present since birth.
  • ionizing radiation: High-energy radiation that is capable of causing ionization in substances through which it passes; also includes high-energy particles.
  • microcephaly: A neurological disorder which causes the affected person to have an abnormally small head due to a failure of brain growth.

The medical effects of a nuclear blast upon humans can be put into four categories:

  • Initial stage: the first 1–9 weeks; the period with the greatest number of deaths—90 percent due to thermal injury and/or blast effects and 10 percent due to super-lethal radiation exposure.
  • Intermediate stage: from 10–12 weeks; deaths in this period are from ionizing radiation in the median lethal range.
  • Late period: lasting from 13–20 weeks; this period shows some improvement in survivors’ conditions.
  • Delayed period: from 20+ weeks; characterized by a variety of complications.

Ionizing radiation from fallout can cause genetic effects, birth defects, cancer, cataracts, and other organ and tissue defects. By directly or indirectly ionizing, radiation can affect a cell’s ability to conduct repair and reproduction. Exposure to even relatively low doses of radiation has been shown to generate genetic damage in the progeny of irradiated rodents. This damage can accumulate over several generations.

In humans, microcephaly is the only proven malformation, or congenital abnormality, found in the developing human fetuses present during the Hiroshima and Nagasaki bombings. No statistically demonstrable increase in congenital malformations was found among the later-conceived children born to survivors of the nuclear weapons at Hiroshima and Nagasaki. Surviving women of Hiroshima and Nagasaki—even those exposed to substantial amounts of radiation—had children with no higher incidence of abnormalities than the Japanese average.

image

Microcephaly: MRIs of a normal individual (left) and a patient with microcephaly (right).

Measuring Radiation Exposure

Radiation dosimetry is the measurement and calculation of the absorbed dose from exposure to indirect and direct ionizing radiation.

Learning Objectives

Define the terms used to define radiation exposure, the gray (Gy) and sievert (Sv)

Key Takeaways

Key Points

  • Radiation dosimetry is the measurement and calculation of the absorbed dose in matter and tissue resulting from exposure to indirect and direct ionizing radiation.
  • Dose is reported in gray (Gy) for matter or sieverts (Sv) for biological tissue.
  • There are several ways of measuring doses from ionizing radiation, including personal dosimeters and ionization chambers.

Key Terms

  • dosimetry: The measurement of doses, especially of ionizing radiation.
  • joule: The derived SI unit of energy, work, and heat; equal to the energy of one watt of power for a duration of one second; symbol: J.
  • sievert: The derived SI unit of radiation dose that is a measure of the health effect of low levels of ionizing radiation on the human body. Symbol: Sv.
  • gray: The derived SI unit of radiation dose defined as the absorption of one joule of radiation energy by one kilogram of matter. Symbol: Gy.

Radiation dosimetry is the measurement and calculation of the absorbed dose in matter and tissue resulting from exposure to indirect and direct ionizing radiation. It is a scientific subspecialty in the fields of health physics and medical physics that is focused on the calculation of internal and external doses from ionizing radiation.

Gray vs. Sieverts

Dose is reported in gray (Gy) for matter or sieverts (Sv) for biological tissue, where 1 Gy or 1 Sv is equal to 1 joule per kilogram. Non-SI units are still prevalent as well, where dose is often reported in rads, and dose equivalent in rems.

Radiation dose refers to the amount of energy deposited in matter and/or biological effects of radiation. It should not be confused with the unit of radioactive activity, the becquerel (Bq). Exposure to a radioactive source will give a dose that is dependent on the activity, time of exposure, energy of the radiation emitted, distance from the source, and shielding. The equivalent dose is then dependent upon these weighting factors. Dose is a measure of deposited dose, and therefore can never go down.

Tools for Measuring Ionizing Radiation

The worldwide average background dose for a human being is about 3.5 mSv per year, mostly from cosmic radiation and natural isotopes in the earth. There are several ways of measuring doses from ionizing radiation, including personal dosimeters and ionization chambers. There are a number of types of wearable dosimeters: quartz fiber, film badge, thermoluminescent, and solid state. People use these dosimeters to keep track of exposure, typically if they expect to come in contact with radioactive substances as part of their jobs.

image

Dosimeter: Photo of a direct-reading dosimeter.