http://www.cmaj.ca/cgi/reprint/181/3-4/E50.pdf

Thanks to the suggestion about rewriting it for Blackberry.

I think you would do well if you wrote the program for blackberries as well (if you haven’t since the postings above). We’re given blackberries for work, not iphones (unfortunately…)

“For example, just how much does one’s chance of getting cancer go up by getting a CAT scan? Is this app going to deter patients from getting imaging tests for fear of getting cancer?”

Brenner and Hall’s Nov/2007 NEJM paper suggested that up to 1/3 of CT’s may not be medically indicated in the US, including up to 1 million pediatric CT’s (again, in the US alone).

Some patients already ‘decline’ a e.g. CT in some cases due to radiation risk. I would bet that this is going to be a more frequent occurrence, as more become aware that there are likely, in fact, some risks associated with imaging exams and procedures.

I’m sure some people would rather that this sort of radiation risk information not be spread among the public – but I think most would hopefully agree that if there are risks or thought to be risks associated with a medical exam/procedure, it’s our duty to give full disclosure and tell patients about the risks.

The program is only available for the iPhone and iPod Touch as of now – we’re looking into how difficult it would be to create it for the Blackberry.

The program itself is intended for both patients and physicians. Patients may enter their radiological exams, including the date at which they had them, and be presented with an estimate of the associated cancer risk both for that individual exam, as well as their sum total.

Physicians may use it to look up the estimated cancer risk associated with an individual exam – we have a paper under review that shows there is a lack of knowledge regarding radiation risk (part of the motivation for this program).

In terms of the model used to estimate risk, we grappled with which model to use early on. There are many potential methods by which to estimate associated risk, each of course with its own disadvantages.

The model we chose to use in the end was that used by the BEIR committee – i.e. the LNT (linear non-threshold) model. If the dose response is not is fact linear at low doses (e.g. x-ray), then the risk estimates of course could be much different. However, I think the BEIR VII is arguably the most thorough investigation and review of the available evidence.

We also assumed that the risks are cumulative/additive – BEIR also assumes this risk (though granted, there have been papers both in support and in contradiction to this assumption).

The risk estimates per effective dose are provided within the BEIR VII report (which I think is available online through ?Googlebooks maybe).

The estimates also reflect the age at which a patient has received their exam – a 40-year-old man who had received a CT when they were 20 years old has a different associated risk than a 40-year-old man who had the same CT when they were 25.

In terms of the doses assigned to each type of exam – there is clearly a range depending on the machine used, the settings, the patient size, etc. There are several ‘catalogs’ published in the literature (Mettler’s catalog of radiation doses is probably the best; however, there are a few others). For the exams left, I did OVID Medline searches for each individual exam.

We also left an option for patients/physicians/others to simply ‘write in’ a custom value, if they knew it. In the future, I wouldn’t be surprised if radiation doses are given out to patients following their exam (particularly for CT and nuc’s). (I also wouldn’t be surprised if a formal consent will eventually be required).

There are some effects, for example, hormesis, that are not included in the risk estimates. This is still controversial – and as the BEIR VII chose not to include it following their review of the relevant literature, we did the same.

Finally, an estimate is only as good as the model used – and nearly any model, by definition of being a model, has flaws. The primary purpose of this program is to help increase medical radiation risk awareness.

If anyone tries it, and has any comments/suggestions/etc, please let us know. I included my email above, but it’s:

mark@tidalpool.ca

We hope to update the program with requested changes, additional exams (e.g. low-dose CT screening), etc.

Mark