The use of PET imaging increased rapidly from 2004 through 2008 among Medicare beneficiaries diagnosed with cancer, according to a study published in the January issue of Journal of the American College of Radiology. The researchers surmised that PET primarily serves as an additional, rather than replacement, imaging exam.

In 2001, the Centers for Medicare & Medicaid Services (CMS) began reimbursing for PET exams in the diagnosis, staging and restaging of non-small cell-lung, esophageal, colorectal and head and neck cancers as well as lymphoma and melanoma. However, the impact of this coverage decision on PET volume and other imaging exam volumes remained uncertain.

Bruce E. Hillner, MD, of the department of internal medicine and Virginia Commonwealth University's Massey Cancer Center in Richmond, Va., and colleagues designed an analysis to determine whether physicians use PET as replacement for or in addition to CT, MRI or bone scintigraphy.

The researchers analyzed Medicare claims for beneficiaries diagnosed with a PET-covered cancer from 2004 to 2008. The study population comprised approximately 125,000 beneficiaries. To be included in the study, a beneficiary was required to have a hospital admission for an ICD-9 classification of one of the six covered cancers or two nonhospital claims occurring seven or more days apart within a year for one of the cancer diagnoses.

Among the entire study population, use of CT remained consistent from year to year within cancer types, but differed among various types. CT days per person-year for beneficiaries diagnosed with esophageal and lung cancer tripled those of melanoma patients.

“The use of PET for all cancer types approximately doubled, from 0.38 to 0.70 imaging days per cancer person-year, an annualized increase of 18 percent per year,” wrote Hillner and colleagues. During the five-year study period, use of scintigraphy dropped 38 percent.

The primary finding of a sustained growth in PET imaging for all cancer types was not matched with a decline in body CT imaging, except for a slight decline among patients with lymphoma. CT imaging increased by 3 to 4 percent per year from 2004 to 2007, and declined 6 percent in 2008.

“Our analysis of individual-level clustering and sequencing suggests that about half of PET/CT is as an additional test to CT, and about half is temporally unrelated to CT,” wrote Hillner et al. The researchers attributed the additive use of PET to several factors: the desire to resolve inconclusive CT findings prior to initiation or change of treatment and interest in addressing clinical questions not answered by the preceding CT.

According to the researchers, estimating the use of PET as a replacement for CT was more complicated because CT volume did not change significantly during the study period.

Hillner and colleagues observed that there was a failure to switch from body CT to PET/CT, but could not determine if the failure was related to quality of care or financial incentives because of oncologist-owned CT systems. “Current guidelines, the rarity of randomized trials and a general lack of rigor in assessing imaging technology are part of the problem,” they wrote.

The researchers’ future plans include a study to identify any links between PET and the prevalence of active treatment in the last few months of life. “Whether PET is associated with superior patient outcomes and affects overall costs will require either studies that measure changes in major decision points along a cancer's natural history or studies that directly measure outcomes,” Hillner and colleagues wrote.