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| Fig. 1: Classical Andrews lymphocyte depletion curves and accompanying clinical severity ranges. [4] (Image Source: A. Klingberg) |
Acute radiation syndrome (ARS) is defined as the collection of symptoms that occur after a portion or the entirety of the body is exposed to a high-dose of radiation. [1] Nuclear radiation causes harm through cellular death (apoptosis) or by inhibiting cellular division (blocking mitosis). [2] The radiation that causes ARS is large enough in dosage such that it is able to penetrate the body and affect internal organs. [3] Cellular damage takes place on the order of microseconds after initial exposure to the radiation dose. [3] The amount of radiation a person is exposed to is measured in Grays (Gy), which is a unit of absorbed dose. [4] One Gray is defined as being equal to 1 joule of ionizing radiation energy deposited per kilogram of tissue. [4] For ARS to occur, a total dose of around 0.7 Gy or more must be delivered to the body. [3]
ARS is defined in four clinical stages, as shown in Table 1.
The first stage is the Prodromal Phase. It is characterized by nausea and vomiting. Other symptoms such as a fever, headache, and abdominal cramping may also occur. [4] This phase typically lasts for less than 48 hours.
The next stage of ARS is the Latent Phase. Outwardly the patient will appear to be improving in health. Unfortunately, the body's supply of pluripotent stem cells, which replenish lost cells, has been severely reduced. [4] Depending on the radiation dose, this phase can last from anywhere between a few days to a few weeks.
The third stage of ARS is the Manifest Illness Phase. The severity of health effects experienced during this phase are dependent on various factors such as the level of radiation exposure, overall volume of the body irradiated, underlying health effects, and age. [4] The illness is divided into three major syndromes: hemopoietic, gastrointestinal, and nervous system syndromes. [5] These syndromes focus on damage to the bone marrow, small intestine, and the brain and neurovascular system.
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| Table 1: Description of phases of ARS. [1] |
The final stage is either recovery or death. The recovery process from radiation exposure may take anywhere from several weeks to several years. [4] If the dose of radiation absorbed by the body is too severe for recovery, death may occur in a few days to a few months. [4] Hemopoietic and gastrointestinal damage are the main cause of death for radiation doses less than 15-20 Gy. [5] Death from direct exposure to radiation of the brain occurs at doses greater than 100 Gy, and combined neurovascular damage is the main cause of death for doses in between. [5]
The quickest way to get an estimate of the level of radiation exposure a patient has received is to measure absolute lymphocyte count. [4] By measuring the lymphocyte count over time and comparing it against a classical Andrews lymphocyte depletion curve (Fig. 1), the severity of ARS can be estimated. [4] Patients suffering from ARS generally fall into three categories: those who recover with minimal care, those who require intensive care (including procedures such as bone marrow transplantation), and individuals who will succumb to the illness (thus requiring palliative care). [4] For most individuals, the care they receive during the prodromal phase will be similar. In the prodromal phase, after all external radiation contamination has been removed from the patient, a focus is placed on symptomatic treatment and the replacement of fluids and electrolytes. [4] If surgery is necessary, it should be conducted within the first 36 hours and not after 48 hours. [6] Additional surgical procedures should be performed no earlier than 6 weeks after the initial radiation exposure to ensure there are no surgical complications due to cytopenia and immunosuppression. [6]
Although rare, ARS is a serious illness that requires immediate care and careful management. As the severity and onset of ARS is very much dependent on the dose of radiation received, it is important for health care providers to properly assess and monitor a patient to ensure they have the highest possibility of recovery. [4] Even in cases of low to moderate radiation exposure, ARS can take a significant time to recover from and may require lifelong medical follow up. [4]
© Andrew Klingberg. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] M. M. I. Garau, A, L. Calduch, and E. C. López, "Radiobiology of the Acute Radiation Syndrome," Rep. Pract. Oncol. Radiother. 16, 123 (2011).
[2] A. Hobson, "The Biology of Radiation Sickness," Physics 241, Stanford University, Winter 2018.
[3] M. Bae, "Acute Radiation Syndrome," Physics 241, Stanford University, Winter 2017.
[4] E. H. Donnelly et al., "Acute Radiation Syndrome: Assessment and Management," South. Med. J. 103, 541 (2010).
[5] J. J. Conklin and R. I. Walker, Military Radiobiology (Academic Press, 19897).
[6] M. López and M. Martín, Medical Management of the Acute Radiation Syndrome," Rep. Pract. Oncol. Radiother. 16, 138 (2011).