High-tech scans could save lives by detecting lung cancer in its earliest stages, researchers suggest.
Smokers were scanned in the study
Scientists combined computed tomography (CT) and positron emission tomography (PET) scanning to pick up tumours.
In Europe, only 10% of lung cancer patients are alive five years after diagnosis.
But experts say more research is needed before screening programmes using the expensive scanning technology are introduced.
Lung cancer kills around 1.3 million people worldwide each year, more than any other cancer.
Research published in the Lancet looked at the benefits of combining the two forms of high-tech scanning.
In spiral computed tomography (CT), images are taken as the scanner revolves around the body.
Its advantage over conventional CT scanning - where images are taken at different angles - is that can take continuous scans faster and at a higher quality.
Positron emission tomography (PET) involves giving a patient a small amount of a radioactive drug which can then help the scanner detect the tumour.
Both techniques are very expensive, and are not widely used in the UK.
It was already known that low-dose spiral CT chest scans could effectively detect early-stage lung cancer in people at high-risk, such as heavy smokers.
But it also detected a high number of false-positive results because it also highlights benign lesions in the lung.
Researchers from National Institute of Cancer and the European Institute of Oncology in Milan, Italy looked at whether using PET scanning increased the accuracy of spiral CTs.
Over 1,000 heavy smokers aged 50 or over, who had smoked at least 26 cigarettes a day for 37 years were given yearly CT scans with or without PET, for 5 years.
If lesions measuring up to 5 mm were detected, they were deemed to be non-suspicious, and the patients scanned again after 12 months.
After a year, 11 cases of lung cancer were detected, with 11 more detected a year later when patients with lesions measuring less than 5mm at the first check-up had been scanned again.
Twenty-one our of the 22 tumours were removed successfully.
There was one death from lung cancer.
Dr Ugo Pastorino of the National Cancer Institute, who led the study, said : "We have shown that low-dose spiral CT combined with selective use of PET can effectively detect early lung cancer.
"A more conservative approach to very small CT-detected nodules is justified, and lesions up to 5 mm can be followed up at 12 months without major risks of progression."
He said more research was needed to inform decisions about widespread screening of high-risk patients.
But Cancer Research UK's Dr Siow Ming Lee, a consultant medical oncologist at Middlesex and UCL Hospitals said: "The issues surrounding the systemic use of PET to detect early-stage lung cancer are highly-charged, complex and controversial.
"No properly conducted randomised trials exist showing that PET screening improves mortality in early lung cancer and there are enormous implications in terms of costs and man-power if screening is to be introduced.
"The new study using spiral CT followed by PET in an attempt to improve sensitivity of detection for early lung cancer is a step in the right direction, but the approach needs to be tested in a properly designed randomised trial.
"The true significance of detecting these small tumours in screened patients is also unclear, and again, we'll need rigorous trials to provide the answer."