Answer to Question #11637 Submitted to "Ask the Experts"
Category: Radiation Basics
The following question was answered by an expert in the appropriate field:
Does the radioactivity of particular organs or tissues in the body change with particular diseases?
The answer to this question depends on whether you are referring to natural radioactivity that affects us all or whether you are referring to man-made radioactivity introduced into the body with a specific purpose in mind. Let's look at both interpretations.
Referring to naturally occurring radionuclides, we all accumulate rather small amounts of various radionuclides as a consequence of living on the earth and eating food, drinking water, and breathing air that contain these radionuclides. Among the more common radionuclides that accumulate to varying small degrees in the human body are hydrogen-3 (tritium or 3H), carbon-14 (14C), potassium-40 (40K), thorium-232 (232Th), uranium-235 (235U), uranium-238 (238U), radioactive progeny of radon-222 (222Rn) and radon-220 (220Rn), radium-226 (226Ra), and other even less significant radionuclides. There can be quite large variations among the extents of any or all of these radionuclides in people, depending on where they live and what they eat and drink.
Having said that, we can begin to address your question by saying that yes, it is possible that the specific health of an individual could affect the degree to which he or she might take up or eliminate certain radionuclides. For example, among the radionuclides listed, 40K is probably the most ubiquitous in terms of uptake by the world population. Stable potassium appears as an electrolyte in the body and is an absolute requirement for proper nerve and muscle function. The radioactive potassium isotope 40K is present to a very small extent in all potassium on the earth, in food that we eat, and in some water. If an individual suffers from potassium deficiency as a consequence of restricted diet or some disease, then the quantity of both stable potassium and radioactive 40K in his or her body will be less than what one would expect if that individual were healthy. For individuals with a noticeable body burden of 226Ra (individuals with diets rich in Brazil nuts might fall into this group), almost all of this radionuclide would reside in the bone because radium behaves biochemically like calcium. If such an individual changed his or her diet to restrict the radium intake, the bone concentration would slowly fall; a similar result might occur if the individual suffered from noticeable bone loss as a result of a bone disease.
It is possible also that some individuals might be exposed to man-made radionuclides and accumulate them in some tissues of the body. For example, individuals exposed to radioactive iodine typically concentrate the iodine in the thyroid gland. An individual who suffered from marked hypothyroidism might concentrate less of the iodine than a person with a normal or hyperactive thyroid gland. Individuals who had thyroid problems, hyperthyroidism, hypothyroidism, or possibly surgical removal of the thyroid would likely exhibit different characteristics from normal with respect to uptake and excretion of radioactive iodine.
In fact, the field of diagnostic nuclear medicine uses a radioactive iodine uptake test to determine the nature of thyroid functional problems of patients. There are a large number of diagnostic tests that use various radioactive administrations to confirm or negate certain health problems by looking at the extent of uptake and/or the distribution of the radioactive species among particular tissues.
In any case, it is important to note that there is a significant amount of individual variability in terms of the degree to which people take up, concentrate in various tissues and organs, and excrete radionuclides. Additionally, for a given individual, the amount of a naturally occurring radionuclide that is in the body or excreted from the body over a given time is affected by his or her particular exposure to that radionuclide, the diet being the most likely influencing factor under routine conditions.
Given these considerations, if one were to try to establish a correlation between the amount of a natural radionuclide in or excreted from the body and the presence of disease, one would have to first establish reliable baseline levels for the individual and ensure that during the study the exposure conditions (e.g., dietary intake) remained constant. This especially applies to naturally occurring radionuclides that are incidentally taken into the body through natural processes, are typically present in relatively small quantities in the body, and are subject to considerable normal variability, as opposed to man-made radionuclides administered for diagnostic purposes.
In the case of radioactive administrations in nuclear medicine, the radionuclides used are most often not found naturally in the body and are administered in amounts that are relatively large (compared to activities of natural radionuclides in the body). Based upon prior knowledge (such information having been obtained from independent research) of the extent of uptake by various tissues and organs, the distribution of the radionuclides among the various tissues, and the clearance time from the tissues in a normal individual (there is often a range of expected results that would be considered normal), a physician can make sound judgments as to the likelihood of specific health disorders from the results obtained.
In summary, the amount and concentration of some radionuclides present in various tissues and organs of the body or introduced into the body may change as a consequence of specific diseases or physical disorders that may alter the uptake, excretion, and distribution of the radionuclides. For some situations such changes are used to our benefit in diagnosing ailments through controlled nuclear medicine administrations.
George Chabot, PhD