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Solitary pulmonary nodules (SPN) remain a common and difficult diagnostic problem. These usually appear as a small, roughly circular object in the lungs (sometimes literally referred to as a spot on the lungs). However, solitary nodules are not always cancerous and have many different causes including primary lung cancers, metastases from cancers at other primary sites and benign (non-cancerous) lesions that include benign tumors, infections, scarring, etc. In addition, cancerous and non-cancerous nodules are almost equally likely. In one large study, 44% of all SPNs observed on CT were benign. Unfortunately, there are few agreed upon image findings to distinguish benign from malignant nodules; the only nodules that are called benign with any degree of confidence are those with certain specific patterns of calcifications.
In the United States, lung cancer screening programs have recently commenced at many institutions primarily due to the research published in the United States, Japan and Germany. These programs all use CT imaging to detect lung nodules at an early enough stage so that treatment options can be effective. These screening programs are actively discovering solitary nodules in their population, and a significant number (up to 90% in one study) will turn out to be benign.
When a patient has an SPN detected, some follow-up tests will be performed to determine whether that nodule is cancerous or not. Typically, a computed tomography (CT, sometimes known as CAT) scan is used as a follow-up procedure to look for calcifications or other findings that may indicate whether the SPN is cancerous or not. If the results of that scan are not clear, then other options may include (in order of increasing invasiveness):
• Follow-up using a chest X-ray, another CT scan or, in some institutions, a positron emission tomography (PET) scan (if the nodule is > 1.5 cm in diameter). The PET scans are used to determine if the SPN has a high rate of metabolic activity that is associated with cancers. Two years of follow-up using chest x-ray or CT scans with no increase in the size is a common indicator of a benign nodule.
• Biopsy – an invasive procedure in which a small needle is inserted through the chest wall, into the nodule to obtain a tissue sample which is then analyzed to determine whether its cells are cancerous or not. This procedure has an accuracy rate that ranges from 60-95%, but has some risk of complication because the lungs are penetrated.
• Surgery – an invasive procedure in which the surgery is performed to penetrate the lungs and remove the suspect nodule.
While biopsy and surgery may ultimately determine the nodule’s diagnosis, recent studies have shown that up to 52% of SPNs that underwent biopsy were benign, and therefore, possibly could have been avoided.
The aim of this research is to perform a retrospective data collection of CT images already acquired for patients who have been evaluated for solitary pulmonary nodules. We will then apply computer analysis techniques (developed under other funded research projects) to this image data to see if certain characteristics of the nodule (its size, shape, density, internal texture, etc.) can be used to help determine whether the nodule is cancerous or not. We are investigating this approach to create an accurate and noninvasive test so that we can reduce the need for additional, more invasive tests. |
