VIENNA - Cancer patients undergoing full CT staging may not always need a bone scintigraphy exam, thanks to the diagnostic accuracy of multidetector-row CT scanners. A study presented today at the tumor imaging sessions of the 2005 European Congress of Radiology found 16-slice CT to be statistically equivalent to scintigraphy for detecting skeletal metastases -- though scintigraphy seems to have found one additional lesion.
"Can 16-slice MDCT rule out skeletal metastases while staging the soft tissues?" Dr. Ashley Groves asked his audience. Groves is from Addenbrookes Hospital and the University of Cambridge in Cambridge, U.K. "Many patients require both CT and bone scintigraphy as part of the staging process. So if we could show that we could get away with only CT, then we could shorten the diagnostic pathway for the patient."
Over a six-month period, the study examined 43 cancer patients presenting to the nuclear medicine department, who were recruited for an additional 16-slice CT scan acquired from the vertex to the knees. MDCT images were acquired using 1.5-mm collimation and 2-mm reconstructions in all planes, viewed interactively in cine mode on the monitor.
Bone scintigraphy studies were reviewed fours hours after injection of 500 MBq of 99mTc-MDP and acquisition of whole-body planar images on a dual-head gamma camera. Two radiologists reported the images in consensus while blinded to the nuclear medicine findings, Groves said.
"Because of the lack of a histological gold standard, discordant results were second-blind-reviewed, and then reviewed again, this time with all the imaging findings as well as clinical information, and a follow-up of at least 12 months," Groves said.
The radiologists documented any soft-tissue abnormalities in their CT reports, and the patients were asked which exam they preferred. A statistical test of equivalence found that the bone scan detected metastases in 14/43 patients. In all there were 36 concordant cases and seven discordant cases, including three cases positive on scintigraphy but negative on CT, and four cases positive on CT but negative on scintigraphy. Three of the seven discordant cases were resolved on further review, and another three of the discordant cases favored the CT diagnosis.
"In this patient, who had breast cancer, the bone scintigram showed increased uptake in the right hip and also in a thoracic vertebral body," Groves said in reference to a slide. "The CT was initially called normal. There was indeed a second sclerotic lesion in the right hip, and also a lytic lesion seen in the thoracic vertebra."
CT's average exam time of 11.5 minutes compared very favorably with the three to four hours required for a scintigram. However, the average CT exam reporting time of 12.5 minutes for 1,700 axial images seemed more complex. "One would think that a single planar nuclear medicine image is a lot easier going to report," Groves said.
Most patients preferred CT over bone scintigraphy, and the Newcombe-Wilson confidence interval method for measuring equivalence of proportions showed that CT was statistically equivalent to skeletal scintigraphy for the detection of bone metastases (CI 95%, -14% to +18%).
To reach such a conclusion, one can look to the world of pharmacology, Groves said, where the U.S. Food and Drug Administration uses the same Newcombe-Wilson to test the equivalence of two drugs. "If the drugs are within equivalence limits of -20% to +20%, the drugs are said to be (equivalent)," he said.
"We've shown, statistically at least, that CT is as good at detecting bone metastases as bone scanning, and this equivalence is even more likely given the three reporting errors, as well as the follow-up data." Groves said. "Patients undergoing full CT staging may not need necessarily to have an additional bone scan. This should avoid duplication of investigation, save hospital resources, and improve cancer patient management by shortening the diagnostic pathway."
The findings have not altered patient management at his institution, Groves noted, and vertex-to-knee CT imaging has yet to be implemented for routine care. But the findings have "certainly made all the radiologists study the bones a lot more conscientiously than they might have previously done," he said.
Patients with bone pain but a negative CT exam would still be referred for bone scintigraphy, he said in response to a question from the audience.
By Eric Barnes
AuntMinnie.com staff writer
March 6, 2005
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