Radiation dose estimate accuracy improved with SSDE metric

Radiation dose estimates are more accurate when using the size-specific dose estimate (SSDE) metric instead of the volume CT dose index (CTDIvol) metric for reporting and comparing patient dose indices, according to a study published in the March issue of the Journal of the American College of Radiology.

While CTDIvol is helpful in measuring scanner output, it should not be used to indicate patient dose because it doesn’t take into account patient size and therefore doesn’t reflect the patient’s absorbed dose, according to lead author J. Anthony Seibert, PhD, of the UC Davis Medical Center in Sacramento, Calif., and colleagues. As dose awareness increases, many patients are requesting dose information that is then misunderstood. Seibert and colleagues calculated the SSDE and CTDIvol from the CT scans of a pediatric patient to examine the differences in dose accuracy.

The clinical example utilized by the authors described a 14-year-old patient with a four-fold difference in CTDIvol between a presurgical CT exam and a postsurgical CT exam, though the absorbed dose was about the same.

Results revealed a CTDIvol ration of 3.7 between the two scans, which indicated a significantly higher dose was emitted during the post-surgery procedure to the lung area. However, when the SSDE methods were applied, the ratio was reduced to 1.8. Likewise, a CTDIvol ratio for the abdomen area was calculated to be 2.3, while the ratio was reduced to 1.1 using the SSDE methods.

“There are many opportunities for improvement of patient care, and as this example demonstrates, a policy for releasing CT dose information to interested parties should be instituted,” wrote Seibert et al. “Many nuances and details in the reporting of radiation dose can lead to significant overestimates or underestimates, and corresponding misinterpretation can be potentially detrimental to the patient, patient's parents, and even to the institution. At the minimum, a size-specific conversion using SSDE methods should be applied to the CTDIvol reported values before release, if at all possible.”