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Radiation-induced Cancer Risk: Timing Is Important

Radiation-induced Cancer Risk: Timing Is Important

Are medical imaging tests as dangerous — or perhaps more so — than the disease they’re used to detect? It’s a question often asked by patients, referring physicians, and the news media. As radiologists have acknowledged the risk associated with CT scans, the industry has taken steps to keep doses as low as possible without compromising the quality of the study.

However, when making decisions about the use of certain imaging, the timing of radiation-induced cancer risks is also important to consider, according to Harvard assistant professor of radiology Pari Pandharipande, MD, MPH. In the January 2013 issue of Radiology, Pandharipande, also an abdominal radiologist at Massachusetts General Hospital, and her colleagues explored the importance of considering the relative timing of when a patient experiences a disease and when they incur radiation-induced cancer risks from an imaging study.

Diagnostic Imaging spoke with Pandharipande about this research.

Why did you decide to look at the risk associated with disease versus the risk of radiation-induced cancer from CT?

I’m a genitourinary and gastrointestinal radiologist by training, and I read a lot of scans for patients who are being followed with CT after treatment for testicular cancer. As part of my clinical practice, I know they receive a lot of scans at a young age. In collaboration with one of the oncologists here at Massachusetts General Hospital, I became interested in looking at what the radiation-induced cancer risks of those scans were over a lifetime relative to the risks of the disease itself.

When we conducted this analysis, we found that while the lifetime mortality risks from surveillance CT scans are slightly less than from testicular cancer, the loss of life expectancy attributable to the CT scans is much less. This is because of the delayed timing of deaths from radiation-induced cancers relative to deaths from testicular cancer itself.

That’s how this project came about: We want to do the best by these patients, and in that process, we have to try and understand how the risks from CT might affect them. Our goal is to reduce CT-related cancer risks for this patient group, but as a first step, we need to understand how these risks manifest over the lives of these patients.

Why is it important that people are aware of the timing of cancer risks from CT?

The concepts that we present regarding the importance of the timing of radiation-induced cancer risks can be applied to any disease process in which there’s an immediate risk that a physician is trying to avoid through imaging — one that would occur sooner in life than the risk of radiation-induced cancer from imaging. The difference in timing must be considered when you make an imaging decision because timing changes the relevance.

Risks incurred later in life are not the same as those faced in the present. That is the take-home message.

When you boil down this comparison, what is it that policymakers and referring physicians need to realize?

An important element to recognize is that while the metric of “life expectancy loss” does capture the timing of different risks over a population’s lifetime, reported life expectancy loss, in modeling studies, is averaged over a population and isn’t experienced by an individual patient. Most people understand risk as a certain chance of experiencing a particular event in their lives. It’s a challenge to figure out how to explain the importance of timing to a person — to explain what it means and deconstruct it in a way that’s understandable.

I hope this paper highlights that risks from radiation-induced cancers are conceptually difficult and that more research and effort should be placed on risk communication and physician and patient decision-making. Simply pointing out a risk to someone, be it a physician or a patient, is not enough guidance. We have to include the idea of timing, as well.

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