Low-dose protocols for CT-guided biopsies
Low-dose protocols for computer tomography (CT)-guided biopsies are effective and feasible, according to a study in September’s Academic Radiology. Radiologists who implemented these protocols at Northwestern University in Chicago report impressive size-specific dose estimate reductions (SSDEs) for lung and extrapulmonary biopsies. They recommend widespread adoption by interventional and body radiologists to improve patient safety by reducing radiation exposure when these procedures are performed.
A team of radiologists specializing in body imaging, cardiovascular imaging, and interventional radiology have replaced standard lung and extrapulmonary CT protocols with low-dose exams at the hospital. Standard protocols that had been used in Northwestern’s radiology department involved a helical acquisition and sequential guiding acquisitions with identical imaging protocol. The low dose protocol implemented with the same CT scanner involved a helical acquisition with larger coverage to localize lesions followed by lower-dose sequential scan for percutaneous needle access guidance and to verify sampling.
Lead author Eric J. Keller and colleagues identified 50 consecutive lung and 50 extrapulmonary CT-guided biopsies before and after implementation of the low dose protocol. They measured anteroposterior (AP) thickening and lateral width of each of the 200 patients measured at the level of the target lesion. They calculated size-specific dose estimates from this data for planning and guiding acquisitions. For lung biopsies, they measured lesion density, density standard deviation, and the attenuation of the adjacent parenchyma to calculate signal-to-noise (SNR) values and contrast-to-noise (CNR) values. Biopsied lung lesion size was measured and lesion conspicuity for planning and guidance acquisition was rated on a four-point scale (from inability to visualize lesion to conspicuity adequate for biopsy).
The authors reported that SSDE was reduced 21% for lung biopsies and 36% for extrapulmonary biopsies. Estimated SSDEs were controlled for patient age, gender, physician, total dose length product (DLP), total acquisitions, lesion size, SNR, CNR and conspicuity rating.
All of the standard- and low-dose lung biopsies adhered to the protocol. Protocol adherence for extrapulmonary biopsies was 89% for the low-dose protocol and 84% for the standard-dose protocol. The low-dose protocol was the only variable consistently associated with lower SSDEs for guidance acquisitions. It was also independently associated with lower SSDEs for extrapulmonary planning acquisitions.
The authors encourage radiologists to “implement and combine readily available techniques to reduce dramatically the amounts of radiation exposure for purely diagnostic procedures. They do caution that “radiologists may have to navigate challenges to implementation, such as requirements for newer scanner hardware and software, which are often installed and implemented primarily for diagnostic imaging studies while older scanners are used for CT-guided procedures.”
REFERENCE
- Keller EJ, Lewandowski RJ, Goodwin L, et al. Reinforcing the importance and feasibility of implementing a low-dose protocol for CT-guided biopsies. Acad Radiol. 2018;25(9):1146-1151.