Lifetime risk estimates may distort risk of radiation-induced cancer

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 - radiation dose, CT

Lifetime radiation risk estimates are flawed when used for clinical decision making and fail to capture the delayed timing of radiation-induced cancers, according to a study published Dec. 18 in Radiology. The researchers termed this phenomena the timing paradox.

“Lifetime attributable risk estimates fail to capture the delayed timing of radiation-induced cancer risks and therefore can distort interpretation of cancer risks from CT,” wrote Pari V. Pandharipande, MD, MPH, abdominal and genitourinary imaging specialist at Massachusetts General Hospital and Harvard Medical School in Boston, and colleagues.

Pandharipande and colleagues developed a Markov model to project outcomes in men with testicular cancer undergoing CT surveillance and compare life expectancy losses and lifetime mortality risks due to radiation-induced cancers.

Young men with testicular cancer who undergo CT surveillance after orchiectomy face a low risk of dying from testicular cancer. As this risk diminishes, a low risk of radiation-induced cancer appears and remains for the patient’s lifetime.

The researchers used 33-year-old men with seminoma as the base case and also derived estimates for 23-year-old and 43-year-old men and patients with two subtypes of testicular cancer. They modeled both standard imaging schedules and one in which CT images were performed at alternate visits. Finally, they modeled standard dose (8.3 mSv +/- 2.7) and low-dose (1 mSv) exams.

Based on the results of their analysis, the researchers projected that 33-year-old men with early-stage cancer who undergo CT surveillance incur a 598 per 100,000 projected lifetime mortality risk from testicular cancer, which is slightly higher than the 505 per 100,000 projected lifetime mortality risk from potential radiation-induced cancers.

However, because the testicular cancer risk was more immediate, life expectancy loss attributable to testicular cancer was more than three times greater than life expectancy loss attributable to radiation-induced cancers at 83 days and 24 days, respectively.

These trends were consistent across all the scenarios studied, and the timing paradox was more pronounced in younger men than in older men.

The timing paradox, wrote Pandharipande et al, “renders providers susceptible to distorted perceptions of radiation-induced cancer risks in essentially all imaging scenarios.”

The researchers noted the timing paradox applies to other clinical scenarios, such as diagnosis of appendicitis and surveillance of young patients with Hodgkin lymphoma. In most scenarios, the risks of life-threatening disease are immediate and exceed the risk of radiation-induced cancer, which is a delayed risk.

Pandharipande and colleagues concluded by emphasizing the need for additional studies focused on the relationship between patient and provider risk perception to understand its effect in clinical decision making.