A comprehensive program to reduce CT dose while maintaining diagnostic image quality has paid off for Imaging Healthcare Specialists, according to an analysis in the November issue of the Journal of the American College of Radiology. The practice has assessed its program through the American College of Radiology Dose Index Registry and found some of its protocols expose patients to half the dose of similar sites.
Imaging Healthcare Specialists, a 10-center outpatient imaging network in San Diego County, Calif., signed the Image Gently pledge in 2010 and focused on smart CT protocols customized for each patient and diagnosis, according to John O. Johnson, MD, and Jon M. Robins, MD, both of Imaging Healthcare Specialists. The practice formed a multidisciplinary team comprised of a lead radiologist, lead technologist and CT applications specialist to evaluate CT protocols.
One of the first targets was peak kilovoltage (kVp). Rather than default to 120 kVp for adult CT exams, the practice reviewed the literature and piloted reduced kVp from 120 to 100 in nonobese patients during CT angiography. When subjective feedback rated image quality as excellent, the team expanded the protocol to all patients undergoing diagnostic chest CT and CT angiography with a body mass index less than 30 kg/m 2. The shift yielded dose reductions in the 30 to 40 percent range, and the protocol was introduced in abdominal and pelvic studies.
The practice rarely uses the 140kVp-setting for obese patients because the improved image quality does not offset the increased dose, according to Johnson and Robins. However, the practice uses 120 kVp for some exams not well-served by low-dose imaging, such as dedicated liver, renal and pancreatic studies.
The second avenue for dose reduction was tube current (mA), which is automatically adjusted based on a patient’s weight and size. Imaging Healthcare Specialists experimented with increased noise for auto mA, which decreases dose, until it reached a point at which image quality eroded. The method produced a new low-dose auto mA default.
Length of coverage provided the next opportunity for dose reduction. The practice reviewed each CT protocol to limit the length of coverage (z axis) and number of phases to include only the clinical region of interest.
Other steps in the process included adjusting the pitch to provide the lowest dose possible while maintaining diagnostic quality, limiting double scans and multiphase exams. Although physicians commonly order CT scans with and without contrast, the without contrast phase offers little diagnostic information, according to Johnson and Robins. These exams are discouraged.
Imaging Healthcare Specialists identified several exams that can be performed at a low fixed mA (50-75 mAs) and 100 kVp for all patients. These include CT colonography, CT abdominal and pelvic stone protocols and abdominal or pelvic CT for abscesses after percutaneous drainage. The shift can reduce dose up to 90 percent in some patients.
A final tool in the arsenal is iterative reconstruction software. “Although expensive, it is a highly effective method of reducing image noise and can reduce patient dose by 40 to 50 percent,” wrote Johnson and Robins. The practice uses a third-party tool to achieve dose reduction via iterative reconstruction.
Finally, Imaging Healthcare Specialists emphasized the management aspect of dose reduction. Central to this is a continuous feedback loop, as well as systems to educate staff members and audit compliance. Elements include a “Tech Notes” field in the PACS, where radiologists can provide feedback to techs. The lead technologist monitors the notes to inform further education. In addition, all CT protocols, policies and procedures are available on the intranet; and random audits are used to prevent protocol drift.
“It is possible to perform high-quality CT at a fraction of the radiation dose previously thought possible,” concluded Johnson and Robins.