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Answer to Question #1527 Submitted to "Ask the Experts"Category: Nuclear Medicine Patient Issues — Therapeutic Nuclear Medicine The following question was answered by an expert in the appropriate field: Q
What is the tolerance dose to normal liver from 131I-labelled agents used for radionuclide therapy, in particular 131I lipiodol? How does it compare to the values used by radiation oncologists for fractionated external beam therapy?
A
That's an interesting question, but we don't have an answer to it
because (1) the absorbed dose is probably nonuniform, with certain
cells being "overkilled" by the beta radiation, and others not killed
at all, (2) we are, to my knowledge, lacking a data base of patients
whose livers have been destroyed by radionuclide therapy, and (3) the
answer will vary depending upon whether the liver is normal, aged,
diseased, or injured by prior chemicals, including drugs. I would
expect that physicians would administer such a radiopharmaceutical,
watch liver enzymes, and then stop when tolerance appeared to be
reached. I would assume that patients getting such treatment already
have a potentially fatal disease. One needs to treat to a tolerance
dose because undertreatment will be useless. It would depend upon the
case, but I expect there would be at least some monitoring of liver
function to try to avoid fatal toxicity, but it is necessary to realize
that toxicity is often reversible, and in the pediatric population is
amazingly reversible, so that even the occurrence of toxicity is not
necessarily a reason to stop a therapy that has some chance of success.
From a practical point of view, I would expect that the radiation
exposure range at which one can reach tolerance will be greater than
that for external beam radiation of 1,500-2,000 rad for a single
treatment dose and a total of 3,500-4,000 rad for fractionated doses.
It would therefore be reasonable clinically to do liver function tests
beginning about at the external beam tolerance dose, or perhaps lower
if the liver is aged, diseased, or previously exposed to toxic
chemicals or radiation. I hope this helps.
Carol S. Marcus, PhD, MD, ABNM Professor of Radiological Sciences and of Radiation Oncology, UCLA
Answer posted on 11 January 2002. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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