Answer to Question #12494 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Therapy - Radiation Oncology

The following question was answered by an expert in the appropriate field:


My mother was born in the United Kingdom in the early 1950s with a large protruding birthmark on her side. The birthmark was removed, and at some point during the process she was treated with thorium dioxide. Her mother informed her of this later in her life. Mum is now 67 and she has been diagnosed with cancer of the bile duct, probably as a result of her exposure to thorium. Fortunately, her prognosis is good and we are hoping she'll make a full recovery. My question is actually relating to my own risks (if any). My mother was 36 when I was born. Am I at risk of thorium-related cancers/conditions? If I have been exposed in utero, how would I go about finding out? Thank you!


The short answer is that you are not likely at risk of cancer. Now for some background and explanation.

Thorium, like uranium, is a naturally occurring element in the earth's crust that is radioactive and was created in the formation of the earth eons ago. It was used commercially in the manufacture of the "Coleman lantern" gas mantles to enhanced light output from the camping lanterns. The oxide form of the element is not considered to be very soluble.

A surface application of thorium dioxide might have been applied to you mom's skin to use the low levels of radiation from the decay of the thorium to "softly irradiate" the skin involved and destroy the cells at the surface of the skin. Given the time between the application of the thorium and your birth, assuming about 30 years, if there were any secondary effects from radiation damage, those would be expected to be reflected in the skin in the area about the initial application. The insolubility of the compound would make it unlikely to migrate to her bile duct. I believe her bile duct disease is truly a new disease site from a totally new source.

However, if she was given an ingestible compound such as Thorotrast (a suspension of thorium dioxide particles that was used as a contrast agent during x-ray imaging in the 1930s and 1940s and to a lesser extent in the 1950s), then the compound remains in the body and can result in liver cancer and other forms of cancer, according to the National Cancer Institute. Given its long half-life it is possible that her cancer could result from the therapy she received.

As for your health I do not think you are at risk at all from the thorium treatment your mother had as a child. You did not mention ever seeing the birthmark on her so clearly there was no lasting visual damage from any surface treatment. If she ingested it, it had localized in the body and diminished over the years due to normal bodily functions. The placenta also does a great job protecting the fetus from impurities in the blood. To my knowledge there is no reported evidence that children of thorium dioxide recipients have an enhanced risk of cancer from the mother's treatment. In your specific case the 30 or so years between application and your birth gave her body plenty of time to eliminate the impurity from her body.

I hope this helps you put everything in perspective and wish your mother well.

James B. Smathers, PhD, CHP, DABR, DABMP, FAAPM

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 17 October 2018. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, 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. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.