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Many Kids With Cancer Face Radiation Worries

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More than 40 percent of pediatric oncology patients included in a new Canadian study exceeded the cumulative radiation dose threshold for risk of significant harm.

That startling statistic comes from a five-year retrospective study, published in the October issue of Pediatrics, of 150 children who were diagnosed with new malignancies in 2001. The sample consisted of five 30-patient subgroups, classified by type of cancer: leukemia, lymphomas, brain tumors, neuroblastomas, and assorted solid tumors. The researchers were from the medical imaging department at the University of Toronto and the Hospital for Sick Children in Toronto.

During the five-year time period, the patients underwent a total of 4,338 imaging procedures that involved radiation, with a median of 19.5 procedures per patient. The individual cumulative effective dose (CED) ranged from 0.0015 millisieverts to 642 mSv, with a median of 61 mSv and a mean of 113 mSv. The study notes that the Biological Effects of Ionizing Radiation VII report says there is good evidence for risk of significant harm starting at 100 mSv.

As you might imagine, CEDs varied considerably among the patients: 1.3 percent received CEDs of more than 500 mSv, with 22 percent at more than 200 mSv and 41 percent at more than 100. The median CED was highest among the neuroblastoma subgroup (213 mSv), followed by the lymphoma group (191). Lowest was the leukemia group at 5 mSv.

“CT constituted 30 percent of the procedures but 52 percent of the cohort CED, whereas nuclear medicine constituted 20 percent of procedures and 46 percent of CED,” says the Pediatrics article. Together, CT and nuclear medicine accounted for more than 95 percent of the patients’ total CED.

Continuing improvement in survival rates of childhood cancers makes tracking pediatric radiation doses increasingly important. On the other hand, without the procedures that created the radiation exposure, the patients might not have survived to experience potential radiation-caused harm later in life.

The researchers estimate that exposure to the median CED of 61 mSv at age 10 might create an additional lifetime cancer risk of 1.2 percent. They estimated that a CED of more than 100 mSv would mean an additional cancer risk of 2 percent and a CED of more than 200 mSv would yield an additional 4 percent risk.

The researchers suggest:

  • A risk/benefit assessment for each patient
  • Consideration of such nonionizing imaging techniques as MR and ultrasound
  • Use of age-related dose-reduction protocols
  • Development of ultralow-dose protocols
  • Appropriate follow-up intervals for high-dose procedures

Related seminar: Pediatric Radiology—Clinical and Radiology Perspectives

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