Added CT Risk for Limited-stage Hodgkin's Lymphoma is Minimal
Does the value of surveillance CT scans in cancer patients outweigh the risk of additional cancers caused by the CT's radiation?
By Elizabeth Gardner
A study using mathematical modeling, presented Tuesday during a session on practice guidelines and outcomes research, suggests that the additional risk posed by CT imaging for limited-stage Hodgkin's lymphoma is extremely low.
"There is growing concern about the use of CT for surveillance in young patients with a favorable prognosis, such as those with Hodgkin's lymphoma, due to the risk of radiation-induced cancers," said presenter Kathryn Lowry, M.D., of the Institute for Technology Assessment at Massachusetts General Hospital. "We wanted to estimate the magnitude of the risk of radiation-induced malignancies, to quantify what the magnitude of the benefit of CT needs to be to offset this risk."
Dr. Lowry's research was awarded an RSNA Trainee Research Prize, Resident.
The team's modeling found that the risk of death from a radiation-induced cancer in 35-year-old patients undergoing regular CT surveillance for Hodgkin's lymphoma was no more than 0.3 percent, which translates to an average life expectancy loss of 12 days. The risk of death from recurrent lymphoma was more than 10 times higher. "This result suggests that even a very small mortality benefit of CT surveillance would justify its use," Dr. Lowry said.
The research team used several formulas together to model hypothetical Hodgkin's lymphoma patients who were 35 years old, in remission after chemotherapy, and undergoing seven surveillance CT scans of the chest, abdomen and pelvis over five years. They modeled radiation-induced cancer risks and mortality for 17 different organ systems, to account for specific organs that were exposed during the scans. For comparison, they also modeled cohorts of patients at ages 20, 50 and 65. They based their analyses on published studies, and on data from publicly available sources, including the U.S. life-expectancy tables available from the Centers for Disease Control and Prevention, the BEIR-VII study (Biological Effects of Ionizing Radiation) from the National Academies, and the National Cancer Institute's SEER (Surveillance, Epidemiology and End Results Program) database, which includes cancer registry data from nine states that represent about a quarter of the U.S. population. The CT protocols modeled are those currently in use at Massachusetts General Hospital.
Projected life expectancy losses from lymphoma were 428 days in men and 482 days in women, whereas life expectancy losses from radiation-induced cancers were less than 12 days in men and less than 16 days in women.
The next step is to quantify the benefit of the imaging studies, though Dr. Lowry said the benefit would not have to be large to justify doing the studies–at least from the standpoint of mortality risk. She cautioned that since the research is based on hypothetical patients, it should not be applied to any individual case.