The acute radiation syndromes are cause by a sudden large dose of radiation to the body and depending upon the dose level one will experience either: Cerebral Vascular (a.k.a. CNS) Syndrome, Gastrointestinal (GI) syndrome, or hematopoietic (bone marrow) syndrome. This listed order is the order of severity and of the higher dose levels lead to more severe conditions: Cerebral Vascular (certain death and occurs in 1-3 days for doses over ~100 Gy), GI (certain death occurs in ~10 days for doses of ~10-100 Gy) and bone marrow syndrome (death can occur within 30-60 days when dose is ~0.7-10 Gy, the lethal dose to half the population LD50 is ~4.5Gy). In this post we will cover the details of these acute radiation syndromes with the target reader of you the Radiologic Technologist or Radiographer.
Acute Radiation Syndromes
When the body is exposed to very large doses of radiation such as: gamma rays, neutrons, Acute Radiation Syndrome will develop and can quickly lead to death.
There are different types of Acute Radiation Syndromes which develop depending on doses of radiation, and these syndromes vary in time scale and mortality.
In this section we use the x-ray or gamma ray equivalent dose to describe the dose levels.
The lowest threshold for an Acute Radiations Syndrome to take place is a radiation dose of greater than about 0.7 Gray (Gy).
Typically, penetrating radiation such as neutrons, gamma rays, or high energy x-rays, are required to have the effects of acute radiation syndrome.
In case of acute radiation syndrome, the entire body receives high radiation dose (or at least a significant portion of the body). For example, if a hand or finger receives a very high radiation dose, it will not lead to an Acute Radiation Syndrome.
For instance, a radiation worker in a nuclear accident or a survivor after an atomic bomb explosion may develop acute radiation syndrome.
For acute radiation syndromes, the radiation doses are received in a short time (seconds to minutes).
Rad Take-home Point:
- Large radiation Dose > ~0.7 Gy
- Typically, an external radiation source of penetrating radiation such as gamma rays, or neutrons
- The entire body (or most of it receives the dose) receives the dose quickly
Bone Marrow (Hematopoietic) Syndrome
All the blood products in the body are made in the bone marrow, inside of the bones. All the blood products start out as stem cells. Those stem cells later become different types of blood products, and the blood products are constantly being remade inside the bone marrow.
In the body of a normal, healthy person about 1011 -1012 new blood cells are made every day. These new blood cells are being made to replenish the supply.
If full body irradiation takes places, the bone marrow is irradiated, and this radiation prevents blood cells from being generated effectively. The severity of the effects depends on the dose of radiation.
For doses of radiation, down to as low as 0.7 Gy, we can see effects of bone marrow syndrome.
Although symptoms can be observed for radiation doses of less than 2 Gy a dose of at least 2 Gy is needed to be lethal (i.e. LD 0=2Gy). So, you are very unlikely to die if you are exposed to radiation dose of less than 2 Gy.
The radiation dose which will kill half of the population is about 4.5-5Gy (LD 50=4.5-5Gy).
The best treatment is typically to use antibiotics to control the symptoms. In a narrow range of high exposure patients a bone marrow transplant may also be beneficial.
The LD100 for bone marrow disease is about 8Gy. All the individuals in the population will die of bone marrow syndrome if they don’t die of something else sooner.
In bone marrow (Hematopoietic) syndrome, the individuals who die will live about 30 to 60 days after the acute irradiation event.
Rad Take-home Point:
- Blood products made in bone marrow can’t be replenished in Hematopoietic syndrome
- (LD-0, 2Gy),
- (LD-50, 4.5-5Gy)
- When the syndrome is fatal it will be 30-60 days
- Doses 0.7-10 Gy
Gastrointestinal (GI) Syndrome
In case of exposure to higher radiation levels, (~10-100Gy), the patient who has been exposured to the radiation will die of Gastrointestinal Syndrome.
The patients with gastrointestinal syndromes, typically die within only 10 days from the time at which the incident occurs.
There are linings inside of the intestine and crypts (small indentations within the gut). The mucosal membrane covers the inside of the gut including all indentations.
Similar to bone marrow disease the issue here is that the mucosal membrane is replenished constantly and after this high level of irradiation the membrane cannot be replenished.
In such cases, GI syndrome leads to vomiting and diarrhea. This becomes fatal, as patients don’t have ability to keep water in the body.
If you have radiation dose above 10Gy, the GI syndrome will be fatal within 10 days. This occurs more quickly than bone marrow syndrome as the cells are replenished more quickly and the symptoms are more severe than bone marrow syndrome.
Rad Take-home Point:
- GI track lining can’t be replenished
- This leads to vomiting, and diarrhea
- This syndrome is fatal in ~10 days
- Doses 10-100 Gy
Cerebral Vascular (a.k.a. CNS) Syndrome
Cerebral Vascular Syndrome sometimes is called Central Nervous Syndrome (CNS) and this is worst and least understood case of the acute radiation syndromes.
It is more appropriately called Cerebral Vascular Syndrome because it is primarily an issue caused by the vasculature, even though it is occurring in the brain.
However, since it was originally termed Central Nervous System (CNS) Syndrome some still refer to it as such.
If only the brain stem is irradiated, such a dose won’t lead to the symptoms of Cerebral Vascular Syndrome as the vascular system has not been affected.
When the body receives these very high radiation doses breakdown of the cerebral vascular system leads to increased fluid within the brain. Since the skull is rigid this leads directly to an increase in pressure within the skull.
This pressure causes symptoms of: vomiting, diarrhea, disorientation, and disability to balance.
It is fatal within one to three days.
These symptoms have been reported down to 80Gy but, typically, they happen with radiation doses around 100Gy and higher.
Rad Take-home Point:
- Breakdown of the vasculature leads to increased fluid in the brain, and increased pressure on the brain
- This leads to vomiting, diarrhea, and disorientation
- This syndrome is fatal in 1-3 days
- Doses greater than 100Gy
Summary Table (Acute Radiation Syndrome)
Here is a quick table with the essential facts about Acute Radiation Syndrome to summarize the information given in the individual sections above.
|Approx. Radiation Dose Levels||Outcome||Timeline|
|Hematopoietic (Bone Marrow)||0.7-10 Gy||Potentially Fatal (LD50=4.5Gy)||30-60 days|
|GI (Gastrointestinal)||10-100 Gy||Fatal||~10 days|
|CNS (Cerebral Vascular)||Greater 100 Gy||Fatal||1-2 days|