The American Cancer Society (ACS) estimates that more than 130,000 new cases colorectal cancer will be diagnosed in the United States, making it the third most common cancer diagnosed in both men and women. It’s also the second leading cause of cancer-related deaths in the US, with nearly 50,000 deaths from the disease expected in 2015.
At the same time, the death rate from colorectal cancer has been dropping in both men and women in the past 20 years, due in large part to improved screening for the disease. The ACS recommends screening beginning at age 50 for men and women with no known risk factors, such as family history or inflammatory bowel disease. Usually screening means a standard colonoscopy once every 10 years, in which doctors use a scope to detect and remove polyps that might develop into cancer.
But standard colonoscopies are rather invasive, to say the least—it uses a colonoscope that gets advanced through the entire colon. The procedure also requires patients to ingest a laxative solution to clean out their systems before the procedure, undergo sedation and refrain from driving for the day. Apprehension about traditional colonoscopies may cut into screening rates.
The University of Chicago Medicine is a leader in an alternative “virtual colonoscopy” that uses a special CT scan to create 3D images of the colon that doctors can use to screen for polyps. The ACS endorses virtual colonoscopies for screening every 5 years. The procedure is far less invasive, often uses a milder preparation solution, and doesn’t require sedation. Physicians or trained technologists insert a small, soft tube into the rectum and inflate the colon with a small amount of carbon dioxide gas. Technologists then use a fast CT scanner to capture images, and that’s it. The entire procedure is over in about 20 minutes.
“It’s a very safe test. It’s less invasive, doesn’t require sedation, and you can go back to work the same day,” said Abraham Dachman, MD, professor of radiology and a national leader in using advanced imaging for screening procedures.
Dachman said colon cancer is one of the best types of cancer for advanced screening. Polyps can take up to 10 years to become malignant, so with regular screening, physicians have a chance to detect trouble spots early.
Once the CT scan is complete, the images are run through sophisticated software that creates a 3D version of the patient’s colon. Using a workstation, Dachman can use the software to “fly through the colon,” as he puts it, navigating through it like a video game to look for any abnormalities.
As he navigates the 3D model, Dachman can zoom in on a particular detail and color-code features such muscle, fat, liquid and soft tissue density (a potential polyp) to help with the screening. The 3D images are linked to the 2D CT images of the same area, which Dachman jump over to for “problem solving” any suspicious areas.
He’s looking for polyps larger than 5mm in diameter, which have the potential to become cancerous. If he finds one or two larger than this but less than a centimeter, he recommends a follow up scan. Any polyps larger than a centimeter, or 3 or more in the 6-9mm range leads to a standard colonoscopy to remove them.
Dachman has been doing research on using the virtual colonoscopy at UChicago since 1996. While it’s becoming more widely accepted, it’s still primarily available at large academic medical centers. Dachman said he hopes that as patients learn about this faster, more comfortable option to standard colonoscopies, it will increase screening rates.
The National Colorectal Cancer Roundtable (founded by the American Cancer Society and Centers for Disease Control and Prevention) has a goal of screening 80 percent of the eligible population by 2018, and I think virtual colonoscopy can help reach that goal,” he said.