Thallium Stress Test and Cancer

[Hello_80]

Hello Everyone:

I am new here; But was wondering if thallium stress test causes cancer (blood cancer) later in life? I saw a canadian study online (http://www.cmaj.ca/content/early/2011/02/07/cmaj.100463.abstract) I hear the radiation from a single thallium stress test is equivalent to 1200 chest xrays. Don't you think that is very dangerous for our blood cells? Anybody with adverse effects? As you all know it takes five years for solid cancers to develop and at least two years for blood disorders after radiation exposure.

[CCFHeartMD10]

Many medical tests, such as x-rays, CT scans, and Thallium scans, use ionizing radiation, while others, such as MRI and ultrasound, do not. Ionizing radiation is associated with a very slightly increased risk of various types of cancer. Therefore every effort is made to reduce the dose to as low as possible, and to shield patients and staff from ionizing radiation. The amount of risk is extremely difficult to measure, as the effects of Ionizing radiation do not become apparent for a long time afterwards. You quote a figure of 5 years for a solid tumour, which is probably shorter than most estimates. This illustrates the difficulty involved. However the increase in risk from a single Thallium test is minimal. When patients undergo multiple scans, the risk can add up. So a sensible approach is to limit Ionizing radiation as much as possible, and to use tests that don't use ionizing radiation if possible. However, the risk of the test must always be balanced against the benefits of the information gained. Sometimes tests using Ionizing radiation are neccessary as the alternatives won't give the same information.
It is important to note that this issue has generated a lot of debate in the medical community. The study you quote had a number of important limitations, which are discussed in the letters to the editor. The main limitation is that the patients they studied seemed to have a higher risk of cancer at baseline than the general population, thus the results may over-estimate the risk of these scans.

[Hello_80]

Hello:

In my opinion I don't think it is appropriate to evaluate or base risk of these radionuclide based on data extrapolated from external sources of radiation. And l really don't think the risk from a single Thallium scan to be minimal; instead it is very significant. The risk from this radionuclide comes in two forms: one the radiation they emit and second by the process they decay (i.e. Auger decay is highly mutagenic). This is specially true in the case of Thallium 201. Believe it or not there aren't enough studies out there to evaluate their intracellular activities. As a matter of fact current dosimetry underestimates the micro dosimetry  by about  15 folds. From what little information is out there,  it points to their genotoxicity and cytotoxicity. In short there are no long term studies done to evaluate their mutagenicity. The few studies done so far point that they are capable of inducing significant chromosomal aberrations - a risk for cancer.  In addition the current estimate of risk for cancer from a single thallium scan is 1:500 to 1:1000 (i.e. This estimate doesn’t account for many of the rare cancer sites that collectively account for  30 or more percent of the cancers in the US).  If these have been included the risk would be higher by several folds. Also this estimate is for an elderly person with a shorter life expectancy. For a younger person it is several folds higher (i.e. due to longer life expectancy and as their cells are expected to divide more in the future and are expected to live through the latency period (i.e. 10 to 40 years)).  

[Hello_80]

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[curmudgen]

I can't be as bad as you claim, however start with this web page

http://www.texasheart.org/HIC/HeartDoctor/answer_189.cfm

also search ' radiation thallium stress test' and look at the medical web sites.