The incidence of clinically important PET-negative CT-positive findings in a large clinical PET/CT practice

Objectives The objective of this study is to determine the incidence of clinically important incidental PET-negative CT-positive findings in a large clinical PET/CT population.

Methods Retrospective study of patients who have had PET/CT scans performed at University of Alberta Hospital since January, 2007. All physicians who have reviewed these studies are active specialists in both nuclear medicine and diagnostic radiology, as defined by the Royal College of Physicians and Surgeons of Canada. Numerous clinical parameters were entered into a clinical database, including the presence of incidental PET negative CT positive findings felt to be clinically significant by the reviewing physician. Data was retrospectively reviewed to determine the incidence of PET negative CT positive findings felt to be clinically significant by the initial interpreting physician. Clinically important findings were categorized into very urgent management (within 2 weeks), moderately urgent management (2-6 weeks), non-urgent management (> 6 weeks).

Results This ongoing study has evaluated 501 patients and 47% of cases contained a PET negative CT positive finding. Eight percent of the PET negative CT positive findings were considered very urgent. The percentage of PET negative CT positive findings demonstrated a clear upward trend from patients in the third to eighth decade. The age categories under the third decade may be statistically affected by low scan numbers. The percent of studies with PET negative CT positive findings were about 50% for all the indications except for melanoma. This may relate to a lower average patient age for melanoma cases. The distribution of PET negative CT positive findings according to urgency was similar between interpreting physicians.

Conclusions Clinically significant PET-negative CT-positive findings were found in 47% of cases and in 8% of cases these were felt to be urgent.

Research Support This study was funded by the Vessie Heckbert Memorial Summer Research Award from the University of Alberta