A study published online November 15, 2011, in The Lancet Oncology has found that patients were much more likely to participate in colon cancer screening programs that utilized CT rather than undergo screening with colonoscopy. Even though screening with colonoscopy is more accurate, it is an invasive procedure. Colonoscopy is an internal examination during which a flexible fiber-optic tube attached to an external camera is inserted into the anus, then advanced up through the colon to allow visualization of the inside of the bowels. When utilized for screening purposes, colonoscopy aims to identify precancerous or early cancerous lesions, which can then be immediately biopsied and in many cases entirely removed. Virtual CT colonography, on the other hand, is a less invasive procedure that utilizes X-rays and contrast to create a three-dimensional image of the colon. Patients with any abnormal lesions identified on virtual CT colonography usually then will need to undergo colonoscopy in order to obtain a diagnostic biopsy of the suspicious lesion.
In this most recent study, individuals in the Netherlands aged 50 to 75 years were invited for colon cancer screening. About 6,000 people were offered screening with colonoscopy, and about 3,000 other people were offered virtual CT screening. About 2 out of 10 people offered colonoscopy accepted, compared to about 3 out of 10 people offered virtual CT.
The diagnostic yield for advanced neoplasia cancer was slightly better for colonoscopy versus virtual CT (8.7 percent compared to 6.1 percent). However, since more people accepted virtual CT screening (3 out of 10) than colonoscopy (2 out of 10), the net effectiveness of each technique was similar. The authors concluded that since the net yield was similar for both techniques, that either strategy could be used for population-based screening for colon cancer. Both procedures have side-effects, but this study found little difference in the rate of serious adverse events.
Dr. Perry Pickhardt, a radiologist at the University of Wisconsin, wrote in an accompanying editorial that the study spoke in favor of using virtual CT to screen for colon cancer. Radiologists are the type of physicians that interpret virtual CT scans.
The take-home message from this study is that first of all, screening for colon cancer can detect precancerous lesions and early cancers. The result is that screening will frequently prevent cancer or result in a complete cure. Secondly, if a person is willing to undergo colonoscopy, this study found it to be a better test for screening purposes. If a person is unwilling to undergo colonoscopy, but still wants to be screened for colon cancer, they should be informed that virtual CT screening is good, but not quite as accurate as colonoscopy. Virtual CT exposes patients to ionizing radiation, whereas colonoscopy does not.
Stoop, EM et al. Participation and yield of colonoscopy versus non-cathartic CT colonography in population-based screening for colorectal cancer: a randomised controlled trial. Published online Nov 15, 2011 by The Lancet Oncology.
Health Physics Society. Radiation exposure from medical exams and procedures.