PET teams with CT for lung cancer screening

September 5, 2003

The selective use of PET imaging with low-dose spiral CT in high-risk patients effectively detects early-stage lung cancer, according to Italian researchers. Investigators cautioned against using their findings to create a new screening protocol.

The selective use of PET imaging with low-dose spiral CT in high-risk patients effectively detects early-stage lung cancer, according to Italian researchers.

Investigators cautioned against using their findings to create a new screening protocol. Rather, they described their study as a demonstration project aimed to assess several key features relevant to the establishment of randomized screening trials.

"Although prospective randomized trials are the proper instrument with which to measure the ultimate outcome of any screening policy, pilot studies addressing specific technical issues and methods are of fundamental importance in a phase of accelerated development of imaging and molecular technology," said Dr. Ugo Pastorino and colleagues at the Istituto Nazionale Tumori and the University of Milan.

A major concern of CT lung cancer screening is the high frequency of false-positive findings. In this study, 29% of participants showed noncalcified lesions, most of them small enough to warrant observation. Only 9% of patients underwent further investigation of suspicious lesions with high-resolution CT, with or without PET, and in 23% of them, the lesion was malignant.

"We have shown that low-dose spiral CT combined with selective use of PET can effectively detect early lung cancer," the authors said. "A more conservative approach to very small CT-detected nodules is justified. Lesions up to 5 mm can be followed up at 12 months without major risks of progression."

The authors suggest that PET can replace fine-needle aspiration biopsy for differential diagnosis of lesions smaller than 6 mm. Combined with a simplified algorithm for CT assessment, PET enabled researchers to complete the diagnostic workup within an average time of 3.8 months at baseline and 2.1 months at year two, thereby reducing the anxiety related to the diagnostic phase.

Participants underwent yearly low-dose single-slice CT (140 kVp, 40 mAs, pitch 2, 10-mm collimation). Lesions larger than 5 mm were further investigated with high-resolution CT (140 kVp, 220 mAs, pitch 1, 1-mm collimation). Noncalcified lesions larger than 7 mm underwent PET imaging, after high-resolution CT.

Researchers reported results at year two in the August 23 issue of The Lancet.

Of the 1035 high-risk patients enrolled, 298 (29%) had 440 noncalcified lesions. Of these, 95 were recalled for high-resolution CT. Ultimately, 22 cases of lung cancer were diagnosed (11 at baseline, 11 at year two).

PET scans were positive in 18 of 20 cancer cases. Six patients underwent surgical biopsy for benign disease because of false-positive results (6% of recalls, 22% of invasive procedures).

Pastorino and colleagues chose 30 HU as the threshold for a positive contrast-enhanced CT diagnosis. For PET, nodules with standardized uptake values greater than 2.0 were considered malignant. Nodular lesions showing positive enhancement on contrast-enhanced CT or a positive PET scan were candidates for biopsy, whether the two modalities were in agreement or not.

At baseline, 29 individuals (48% of recalled) received a PET scan. It was positive in 11, including in eight of nine participants diagnosed with lung cancer. PET clarified six of 14 cases that were indeterminate at high-resolution CT. On the other hand, PET was the main reason for biopsy in three of five benign baseline lesions.

At year two, 13 participants (38% of recalled) received a PET scan, and 11 were positive. Despite the smaller size of lesions, all but one case of lung cancer was PET positive.

The authors note that CT screening for lung cancer may not reach a sufficient cost-benefit balance to win against competing medical priorities. But they also say that current cost-benefit estimates may be too pessimistic. They suggest that their protocol may fit somewhere in the middle of the debate.

For more information from the Diagnostic Imaging archives:

CT screening for smokers and ex-smokers shows little benefit
http://www.dimag.com/db_area/onlinenews/2003/2003012701.shtml

Amid slings and arrows, ELCAP forges ahead
http://www.dimag.com/db_area/onlinenews/2003/2003031201.shtml

CT screening fireworks fizzle into didactic exploration
http://www.dimag.com/cgi-bin/webcast02/display_news.cgi?49

NCI screening trial begins amidst controversy
http://www.dimag.com/db_area/onlinenews/2002/2002102301.shtml