Lung Cancer Is Better Identified with Ultra-Low-Dose CT Than by Current X-Ray Technology

To better determine which imaging modality works best for the diagnosis of lung cancer, Norwegian researchers have undertaken a pilot study in which they evaluated both X-ray images and ultra-low-dose computed tomography (CT) images of a small sample of patients for whom the researchers knew the correct diagnosis beforehand.

The radiologists who examined the images did not know what was wrong with the patients, but they were aware of being part of a research project, and they were told to search for all possible diseases of the chest region. The findings of the study were remarkable. By studying the X-ray images, the radiologists found the correct answer in only 18% of the cases. In other words, they missed 82% of the diagnoses.

With ultra-low-dose CT, the radiologists made a correct diagnosis in 89% of the instances. “X-rays are taken out of old habit, but with X-ray the cancer is detected too late. It’s therefore smart to use ultra-low-dose CT to be able to detect the disease in time,” stated Dr. Trond Mogens Aalokken, from the department of radiology and nuclear medicine, Oslo University Hospital (Norway).

Each year, nearly 3,000 Norwegians develop lung cancer. Current X-ray examinations capture only 20% of tumors. With advanced ultra-low-dose CT technology, the radiologists detected the condition correctly 90% of the time. In Norway, no other forms of cancer take as many lives as lung cancer. Their prognosis is discouraging: six out of seven die within five years. What is especially unfortunate about lung cancer is that the tumor has plenty of space to grow. It can therefore grow for a long time before being detected.

Most patients have their first diagnosis made by X-ray imaging. Each year, Oslo University Hospital takes 30,000 chest X-ray exams. In Norway, this number exceeds one million. Up to now, there has been no study that has ever examined how well X-ray images function with a view to detecting lung cancer and other diseases of the chest region.

“X-ray technology has remained nearly unaltered for 100 years,” noted Dr. Trond Mogens Aalokken from the department of radiology and nuclear medicine, Oslo University Hospital. In cooperation with a group of physicists at the Intervention Center he has made a comparison of the proportion of patients who obtain a correct diagnosis with X-ray images and how many patients might have obtained a correct diagnosis with CT, which is a much more advanced imaging technology.

Whereas X-ray images are two-dimensional, CT images are three-dimensional. CT images can thus reveal the precise location of the tumor. Up to now, the radiation dose from examinations of lungs with CT has been 100 higher than from regular X-ray examinations. A CT scan is equivalent to five years of natural background radiation. Radiologists have therefore been reluctant to use CT for an initial diagnosis of lung cancer.

If the X-ray exam is negative, some months may pass before the patient is referred for a CT scan. Then, it may already be too late. Recently, CT scanners have become far more effective. The mathematical technique for reconstructing the images has changed completely. This means that the images now contain more data, while the radiation dose has decreased. Researchers from the Intervention Center have now succeeded in generating CT images with the same low radiation dose as a standard X-ray image.

“We still cannot achieve the same high-quality images by replacing standard full-dose CT with ultra-low-dose CT, but we have wondered whether the old low-quality X-ray examinations can be replaced by ultra-low-dose CT. Although the CT dose is nearly as low as for a chest X-ray, we can obtain far more information from the images,” stated Associate Professor Anne Catrine Trægde Martinsen, who works at the Intervention Center and the department of physics, University of Oslo.

Moreover, the radiologists detected 15 times as many false-positives in the X-ray exams. “False positives are a burden on the patient. They also entail unnecessary check-ups, which incur a high cost on society. With an X-ray examination, there is a high likelihood that you will not have any answer as to whether you are ill, and an answer that says that you are ill even though you are healthy. Many are diagnosed too late. This is a dramatic consequence of the fact that the health services give priority to X-ray images above CT images,” Dr. Aalokken stated.

Their research drew attention at the world’s largest medical conference for radiology, the Radiological Society of North America (RSNA), in 2012, held in Chicago (IL, USA). Their academic article was nominated as one of the 10 best from the conference. “Even though our results are extremely convincing, we need to undertake a full-scale test to be absolutely certain,” noted Dr. Aalokken.

Before the diagnostic procedure can be changed, the researchers must calculate the cost to society. “A CT machine costs 10 times more than an X-ray machine, but it is also costly to treat patients with advanced lung cancer. Most people believe that X-ray is a quicker procedure than CT, which is not true. “An X-ray check takes five minutes. A low-dose CT check goes almost as quickly; it takes seven minutes. On the other hand, the radiologists need two to three times longer to interpret a CT image,” Drs. Aalokken and Martinsen emphasized.

Odd Terje Brustugun, associate professor at the department of oncology at Oslo University Hospital and assistant professor at the Institute of Clinical Medicine (UiO), substantiated that Drs. Aalokken and Martinsen’s research is valid. “As far as I have understood, the method can be used on existing, modern CT machines. Before it can replace ordinary chest X-ray some work needs to be done in terms of the resource situation and training of radiographers and radiologists. The method should be tested on a greater number of patients and compared to other techniques on a larger scale before we can conclude how well it works,” Dr. Brustugun stressed.

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