How does your doctor know how much radiation to use in your CT scan? For that matter, how does your doctor know how well any medicine or procedure works? The answer is someone has worked it out in a clinical trial.
When I went for my most recent CT scan, the doctor asked if I would participate in a study to see if there is a better way to determine how much radiation and contrast solution each patient receives. Here is what I learned.
The radiologist who performs your CT scan uses a computer to set the amount of radiation and the volume of contrast solution you will receive. This is called an imaging protocol. The computer takes some variables into account, but in general, a 6’6”, 300 pound man and a 4’11”, 98 pound woman receive the same amounts according to the doctor who explained the study to me. Until recently, there hasn’t been an easy to way to take multiple factors into account to individualize the radiation dosage.
Now an Italian company called Bracco Imaging has developed a computer program that can tailor the radiation dose, contrast volume, and other factors for each patient. However, doctors don't want to use this new procedure unless they know that it will result in images that are just as good as the ones from the old method. If the smaller person needs two CT’s to get good pictures because a lower rate of radiation yielded a blurry picture, then the new technology doesn’t do much good.
So selected hospitals in the United States and Europe will be participating in a trial to find out how well the new system works. With rising concerns about the long-term dangers of radiation exposure from multiple CT scans, this new system could take some of the worry from cancer patients or others with chronic conditions that require frequent scans.
I had been selected randomly to participate in the trial. If I was interested, the doctor would go into more detail. If not, no problem, my CT would be done the usual way. I wanted to know more before I signed the consent forms, and the doctor answered all my questions in terms I could understand. The study might benefit me personally if the patient-adapted protocol called for a different setting than I would usually receive, but there was no way to know until I consented and the computer calculated my protocol. The downside was that it would take longer for my CT because I would need to answer some questions and fill out some forms. A possible drawback was that the picture might be blurry and need to be repeated. If that happened, there would be no additional cost to me.
Even though I was in a hurry to be somewhere else that day, I decided to participate. After filling out the forms, I couldn’t tell any difference in my CT. When I was done, the doctor told me that based on my weight and height, there wasn’t much difference in how my CT was done from the usual. He said the only thing the computer said to do differently was to push the contrast solution more slowly. He said slower administration of the solution was a good thing for people like me with tiny veins. The picture was perfectly clear, so my main hesitation about participating in the trial--fear of a repeat CT--turned out not to be a problem.
The results are not in yet from this study. Films for almost 2,000 patients will be compared before radiologists know whether this system will result in clear images as well as more appropriate levels of radiation and contrast solution. Whatever they find, my CT results will be one point of data used to determine the effectiveness of patient-adapted protocols.
Cancer patients often seek out clinical trials to get the newest medicines or other cutting edge treatments. However, many clinical trials are ones you may come upon by chance. Your doctor or hospital has been asked to try out something new. If the opportunity comes along, don’t consent automatically. Ask questions. Make sure you understand all the risks and benefits. The doctor should give you a clearly stated list of these along with information about who is conducting the trial and why.
Once you understand exactly what you are being asked to do, I hope you will seriously consider saying yes to a trial. The information your doctor learns may help you as well as all the patients who come after you.
Brody, J. Medical Radiation Soars, With Risks Often Overlooked. New York Times. 20 Aug. 2012.
Goldman, L. Principles of CT: Radiation Dose and Image Quality. Journal of Nuclear Medicine Technology. 15 Nov. 2007.