Radiation and Potassium Iodide Quiz

Approximately 2/3 of the BNTVA died from neoplasms between the ages of 50 and 65. All the other answers are incorrect. This data suggest that historical exposure to repeated military nuclear device testing is associated with the eventual development of fatal neoplasm.

The correct answer is “gamma rays”. Gamma rays are high energy photons that include X-Rays. These photons are able to easily pass through human tissue, hence their utility in plain film and CT radiography. Infrared photons (heat) are low energy and don’t easily pass through human tissue. Alpha particles consist of helium nuclei and are unable to pass through clothing, skin, or paper. However, the are a significant radioactive exposure concern in the setting of nuclear fallout and internalization of radioisotopes. Beta particles are either free electrons or positrons and are able to penetrate human tissue by 1 or 2 centimeters. Similarly, most health problems occur when beta emitting radioisotopes are internalized into the patient.

Of all the answer choices above, only Sieverts (Sv) accounts for radiation exposure AND type of radiation exposed to. All of the other units are direct measurements of energy that do not take into consideration the type of radioactive source. This is important because different radiologic sources have differing biologic effects, and these also depend on the exposure. For example, the mSv exposure from a CT scan will be remarkable different than the mSv exposure from a radioactive iodine load.

The thicker the shield is, the less radiation gets through. The denser the shield is, the less radiation gets through. Therefore, the correct answer that amount of radiation that gets through the shield is inversely logarithmically related to the density and length of the shield. The formula is as follows:

The formula does not likely need to be memorized for the purposes of the medical toxicologist; however, the fundamental concept is important.

Due to the spherical nature of radiation when there is a single point of exposure, the intensity of radiation follows the inverse square rule. The inverse square rule means that the intensity of radiation is equal to the inverse square of the delta between the two positions. So, in this question, the delta is 6 meters. Therefore, the inverse square is 1/36. All or the other answers are incorrect.

Radioactive isotopes of radon gas are by the far the most important exposure to United States citizens. The distribution is geographic in nature, with the midwest being predominantly affected. It seeps through cracks in the foundation and collects in basements. When coupled with cigarette smoking, the risk of lung cancer is especially increased. This is because when Radon decomposed into daughter compounds via alpha decay, these decay products become solid and deposit on the bronchial and alveolar epithelium. CT scanning is a less significant exposure to radiation, and the clinical significance of CT scans and future cancer is controversial. Nuclear reactors are relatively safe, unless there is a failure of the containment vessel.

Although fluoroscopy accounts for only 10% of radiologic examinations, it is the most significant source of occupational exposure to radiation. The reason for this is that there are higher intensities of X-rays, there is the possibility of direct operator, and increased scatter from the devices. Plain film x-rays and CT have very limited scatter and low levels of exposure to personnel, especially due to appropriate shielding. Nuclear medicine is not the most common occupational exposure, but patients treated with radioactive iodine, for example, have triggered radiation detectors.

Direct effects of ionizing radiation damage cellular DNA. Induction of free radicals is an indirect effect of ionizing radiation. Chromosomal damage to neighboring cells is termed the “by-stander effect”. Genomic instability of progeny cells is likely due to direct effect of ionizing radiation that was not immediately observable as a result of initial survivability in the setting of significant DNA damage.

The deterministic effect of radiation exposure refers to the probability of death due to an acute exposure, such as seen in nuclear disasters. The stochastic effect of radiation exposure refers to long term sequelae of radiation exposure, such as the development of cancer.

In this formula, 2 points are award to emesis, which can occur due to psychological stress. There can be a delay in hematologic abnormalities and lymphocytes begin to decease before neutrophils, but this is not a major limitation to this method for dose estimation.

The patient in this question is currently in the latent phase of radiation exposure, which occurs immediately after the prodromal phase. The prodromal phase is characterized by GI upset, such as nausea and vomiting. During the latent phase the patient will likely have no symptoms. The shorter the latent phase is, or in other words, the faster the patient develops symptoms, the larger the dose of radiation likely was. The 3rd stage occurs after the latent phase and involves bone marrow suppression, alopecia, and GI upset. This phase usually occurs around 3-5 weeks. If the patient Recovery occurs when the patient symptoms and hematologic abnormalities begin to improve.

The patient likely had a large exposure, and the prognosis is grim. The patient likely a cerebral edema, which is thought to be attributable to break down of the cerebral vasculature, which can occur around 15-20 Gy. Hypotension is also likely due damage to the body vasculature. Exposure to 6 Gy is the usual threshold limit for development of GI symptoms, which are caused by sloughing off of the GI mucosa. Exposure to 6 to 10 Gy can also cause a delayed pneumonitis. Exposure to 1 Gy can cause hematologic abnormalities. Exposure to 0.1 Gy would be less likely to cause symptoms.

The correct order of events for first responders is to dawn universal PPE, travel to a safe distance, decontaminate victims, and then transport the victims to a higher level of care. Ideally victims should be evacuated/transported to areas upwind of the site of disaster. Patients should be decontaminated prior to transport to avoid also transporting potentially dangerous radionuclides, which could lead to spread of contamination.

In this case, the patient’s lymphocyte count is less than 1000/microliter so he should be treated with prophylactic antibiotics and antifungals to prevent opportunistic infections. Keep in mind, that with significant radiation exposure, there is dermal and GI tract breakdown due to apoptosis and necrosis that predispose patients to opportunistic infections, especially in the setting of impending bone marrow failure. Because of suspected bone marrow failure, which is usually seen in patients exposed to more than 3 Gray (Gy) of radiation, the patient should be given cytokine therapy to promote hematopoesis and leukopoesis. Additionally, the patient will likely be immunocomprised so staff should practice reverse isolation, as in neutropenic fever.  Finally this patient should be given anti-herpetic agents due to his history of “cold sores”.

After a nuclear disaster, Uranium degrades rapidly to radioactive Iodine, which has a comparatively longer half life of ~8 days. Administration of KI causes a direct competition of non-radioactive iodide with radioactive iodide, which effectively blocks its transport into the thyroid and incorporation into thyroid hormone. Iodine transported to the cytosol of follicular cells, not medullary cells.

In this case, a pregnant patient who was downwind of a nuclear reactor with a likely significant exposure should be treated with KI to prevent thyroid uptake in both the mother and fetus. KI is pregnancy category D, due to to possible adverse effects on the fetus resulting from modulation of both maternal and fetal thyroid hormone synthesis. KI administration is associated with both hypothyroidism and hyperthyroidism; however, no definite causality has been established. Inhibition of maternal thyroid hormone synthesis is associated with poorer neurologic outcomes of live born infants. Nonetheless, in the setting of a significant exposure, these risks must be weighed against the benefits.