Clinical Impact of Radiologist Interpretation of CT in PET-CT Imaging

Abstract

We assessed whether radiologists’ reading of the CT portion of the PET-CT identifies significant additional lesions and whether these findings result in major clinical management changes.

716 consecutive patients (pts) aged 13–87 underwent FDG PET-CT scans for known or suspected cancer between 07/05–03/06. Only those pts without a diagnostic CT within 1 month prior to the PET-CT were included. The CT portion of the PET-CT was read by a nuclear medicine or radiology resident or fellow with 1 of 3 designated radiologists and dictated separately from the PET report, which was read with 1 of 5 nuclear medicine faculty physicians. Typically the PET portion was read on the day of scan and CT portion next morning. The radiologists were aware of the PET results and had access to fused PET-CT images. The PET-CT system used was a 2-slice Siemens Biograph. Particular attention was paid to 5 major findings, which are not FDG avid: small pulmonary nodules, lymph nodes, pneumothorax, aortic aneurysm, and renal cell carcinoma. Other CT findings were listed as minor.

The major findings identified by radiologists, but not mentioned by nuclear medicine faculty, were FDG-negative lung nodules (typically sub-cm) in 91 pts (12.8%), 43 FDG-negative lymph node/soft tissue masses (6.0%), 1 pneumothorax, 1 pneumoperitoneum, 15 aortic aneurysms (1.9%) and no renal cell carcinoma. This resulted in 21% of all patients having findings. However, major clinical management changes as a result of these findings only occurred in 3 pts: one with a 7-cm AAA who underwent endograft repair and another patient with enlarged right iliac lymph nodes that were subsequently excised. The pt with pneumothorax did not require chest drain. The pt with pneumoperitoneum underwent laparotomy for perforation of duodenal ulcer. The remaining 7 aneurysms are being followed, as are the cases of small pulmonary nodules. Among the minor radiology findings were: calcified granulomas 122 (17%), atherosclerotic calcifications 77 (10.8%), kidney/liver cysts 35 (4.9%), emphysema 39 (5.4%), gallstones 21 (2.9%), and pericardial effusion 19 (2.7%). None of these led to major clinical management changes.

The reading of the CT portion of a PET-CT study often identifies FDG-negative lesions; however, it infrequently leads to major clinical management changes in oncology patients. Nevertheless, given the severity of some of these findings, it seems warranted that that the CT portion of the examination be carefully examined by a physician with appropriate CT experience.