Lung cancer is a leading cause of mortality and CT screening of high-risk patients will likely become routine. Low-dose CT biopsy techniques are necessary to minimise risk to screening cohort.
“The published early results of a trial using computed tomography to detect lung nodules demonstrated that screening with low-dose CT reduced mortality from lung cancer by 20% compared to screening with chest X-rays alone,” said Jeremy Collins, assistant professor of Radiology at Northwestern University in Chicago. “Statistically, many people who undergo screening will have nodules detected with CT and a biopsy may be recommended. We want to minimise the side-effects of the biopsy procedure,” he added.
Collins noted that professional groups and society at large were concerned with the growing population dose associated with CT examinations. The aim of this study was to evaluate the impact of a low-dose CT guidance protocol on dose metrics for lung biopsy procedures.
“All image studies using X-ray technology are going to be associated with a small amount of finite radiation exposure,” said Collins. “Although the jury is still out to some degree, there is general consensus in the community that the radiation dose risk is both linear and additive. Any place where we can reduce the incremental dose for each imaging study is very important because the overall exposure over time can be substantial,” he noted.
The investigators implemented a low-dose CT guidance protocol in August 2010, involving a 120 kVp spiral acquisition with a pitch of 0.8 and 80 mAs for planning, followed by sequential 100 kVp and 80 mAs acquisitions for guidance. Operators determined the imaging volume to be scanned and could modify the CT guidance protocol. All procedures were performed on a single 16-slice CT scanner.
They obtained IRB approval and consecutive CT-guided lung biopsy procedures were identified through case log review of 50 patients before and 50 patients after the protocol change.
Dosimetry data was obtained through PACS, including the number and type of acquisitions, the associated kVp and mAs, as well as the total mAs and dose length product (DLP). Image quality was assessed by a single investigator.
Differences in means of continuous variables were assessed with a two-tailed Student’s t-test.
Results
The study population consisted of 50 lung biopsy procedures in 50 patients before and 50 patients after the protocol change. The low-dose protocol significantly reduced the average DLP for lung biopsy procedures from 747.9 mGy-cm (range, 121– 5,559) to 251.8 mGy-cm (range, 73–715; p<0.0001). There was no significant difference in the number of CT acquisitions for needle guidance between groups (16.3 vs. 14.5; p=0.21). Sequential scanning for needle guidance was utilised in 0 percent (0 of 50) and 100 percent (50 of 50) of procedures before and after implementation. Image quality was adequate for guidance in all procedures.
The researchers concluded that the low dose protocol for CT-guided lung biopsy procedures achieved a dose reduction of 66%, with 100% voluntary adherence to use of sequential scanning for needle guidance. “Interventional radiologists are experts in image-guided procedures and well-positioned to champion low-dose CT-guided techniques for lung nodule biopsy. They should review CT guidance protocols aiming to reduce patent dose and improve patient safety,” they recommended.
“We found that simple modifications to the CT technique used for guidance to perform lung biopsies resulted in a significant dose reduction to individuals treated,” noted Collins. “This was possible while maintaining appropriate image quality for interventional radiologists performing biopsy, and fortunately the modification to the scanner technique is simple and can be applied to any existing CT scanner system,” he added.
