Follow-up scans after treatment for testicular cancer don't appear to put men at higher risk of new tumors, researchers have found.
Men usually get regular computerized tomography (CT) scans to check if their testicular cancer has returned following treatment, but some worry that the associated radiation could be dangerous.
But that did not seem to be the case in the new study, published in the Journal of Clinical Oncology.
Overall, 14 percent of some 2,500 men who received multiple follow-up scans developed new tumors in the scanned area over the decade following their diagnosis. And those who received the most radiation were at no higher risk.
"Even with those incredibly high doses of diagnostic radiation, we did not identify any association between this exposure and an increased risk of cancers," study author Dr. Carl van Walraven at the Ottawa Health Research Institute told Reuters Health.
"To us, it's reassuring," he added, given the fact that more and more people get CT scans, which may increase cancer risks slightly although they are designed to look for disease.
Research has also found that people who get radiation treatment for other cancers are at increased risk for second tumors. For instance, men who receive such therapy for prostate cancer more often develop bladder and rectal cancers.
However, in radiation therapy the dose is typically higher than what people receive during diagnostic scans, explained van Walraven. And previous studies that have looked at the relationship between radiation from diagnostic scans and risk of second cancers have used different methods, making overall conclusions difficult, he added.
"The literature is very unclear whether there is an association between diagnostic radiation exposure and cancer."
Still, half of the men included in van Walraven's study received more radiation than many Japanese atomic bomb survivors, who were at increased cancer risk.
The difference, he suggested, may be how the radiation is delivered. Atomic bomb survivors received a massive dose at one time, while men who get several diagnostic scans stretch out their exposure over several years, which could be less dangerous.
It's possible that these smaller doses, stretched over time, "are small enough that the body can take care of them," said van Walraven. But more research is needed. "We don't know whether or not that's true. But we thought that may be one way to explain our data."
During the study, half of the men received at least 10 CT scans of their abdomen and pelvis within five years of their diagnosis. But only 14 developed tumors in that region during the study period.
One concern with the findings, however, is that the researchers didn't follow the men very long, said Dr. David Brenner, a radiation expert at Columbia University Medical Center in New York, who was not involved in the new work.
On average, the men were only 35 when diagnosed with testicular cancer, and half were tracked for 11 years or less. Yet most radiation-induced cancers in young men "will actually appear 10 to 40 years post-radiation," said Brenner.
So with such a short follow-up, the study will only capture a small fraction of the total cancers that the radiation will induce, he said.
These results "don't really tell us anything about the lifetime cancer risks associated with CT scans," said Brenner.
"I would hope the authors will be continue to study this population over a further 10 to 20 years," he added. "The results should be very informative."
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