Lecture 16

Radiation Exposure

1. Types
2. 1. Irradiation
   2. External Contamination
   3. Internal Contamination

Sequence of Radiation Events in Indirect Action

Medical Diagnosis

1. Acute Radiation Syndrome
   1. ARS encompasses the signs and symptoms experienced by individuals exposed to acute, whole-body irradiation.  Much of the data concerning this condition was collected largely through Japanese atomic bomb survivors at Hiroshima and Nagasaki.  In addition, it has been well characterized using an animal database. 
   2. A lethal dose of radiation for humans is 8 Gy.
2. Prodromal Radiation Syndrome
   1. PRS encompasses the early symptoms that appear after radiation exposure.
   2. gastrointestinal symptoms: nausea, vomiting, diarrhea, anorexia
   3. neuromuscular symptoms: easy fatigability.
3. Hematopoietic syndrome
   1. In these cases, radiation suppresses normal bone marrow and spleen functions, causing death even for radiation amounts less than 8 Gy.
   2. Peak incidence of death occurs at about 30 days post-irradiation, though it continues for up to 60 days.
   3. Additional symptoms include: chill, fatigue, hemorrhages,  ulceration, infection and anemia. Death usually results unless patient receives a bone marrow transplant.
4. Gastrointestinal syndrome
   1. Gastrointestinal syndrome typically occurs at doses greater than 10 Gy of gamma-rays (or equivalent).
   2. Death usually occurs within 3 to 10 days.
   3. Symptoms are due largely to depopulation of the epithelial lining of the gastrointestinal tract by radiation.
   4. On record, no human has survived radiation dose >10 Gy.
   5. Clinical symptoms include: nausea, vomiting, and prolonged diarrhea, dehydration, loss of weight, complete exhaustion, and eventually death.
5. Cerebrovascular syndrome
   1. Cerebrovascular syndrome is identified at doses greater than 100 Gy of gamma-rays.
   2. Death occurs within hours from cardiovascular and neuromuscular complications.
   3. Clinical manifestations include: severe nausea, vomiting within minutes of exposure, disorientation, loss of muscular co-ordination, respiratory distress, seizures, coma and death.
6. Radiation-induced Mutagenesis
   1. Note: radiation DOES NOT produce new, unique mutations, but increases the incidence of the same mutations that occur spontaneously.
   2. Incidence of mutation is extremely dose and dose-rate dependent.  For example, a dose of 1 rem per generation increases background mutation rate by 1%.
   3. Today, children of A-bomb survivors from Hiroshima and Nagasaki do NOT show any significant genetic effects of radiation.
7. Radiation Carcinogenesis
   1. Radiation Carcinogenesis is a stochastic late effect.  There is no threshold; it produces an "all or none" effect (and because of this, severity is not dose-related).  However, the probability of carcinogenesis IS dose-dependent.
   2. Leukemia has the shortest latency period of around 5 years. Solid tumors have a latency period of around 20 to 30 years.  Total cancer risk for whole body irradiation is one death per 104 individuals exposed to 1 rem.

Purpura and Vomiting Purpura, or bleeding under the skin, is one of the symptoms of acute radiation sickness. The heavily exposed survivors experienced fever, nausea, vomiting, lack of appetite, bloody diarrhea, epilation, purpura, sores in their throat or mouth (nasopharyngeal ulcers), and decay and ulceration of the gums about the teeth (necrotic gingivitis). The time of onset of these symptoms depends on the exposure level. Long term effects - blindness Radiation can often damage epitheilial cells.  When this happens, damaged cells move to the back of the eye and cause lense opacity by blocking light.  This occurs at a 50% probability for people with a dose of about 50 rad.

Purpura spots. Image courtesy of Hektor. Some rights reserved.

10. Epilation – severe loss of hair
    1. Hair loss is a common sign of radiation exposure & sickness.
    2. Severe epilation (2/3 hair loss) occurs at doses of >200 rad.
11. Radiation impact on Bone Marrow
12. Radiation levels above 2 Gy suppress normal bone marrow functions and causes long term mutation of red or white blood cells.