according to a study published in JAMA Internal Medicine.
Various institutional characteristics, such as allowing any radiologist to establish CT scan protocols, are associated with a greater likelihood of using higher radiation doses. “Dose optimization practices may benefit from being tailored to specific practice types, as well as different organizational structures, to have a higher likelihood of meeting dose guidelines,” wrote Joshua Demb, PhD, MPH, a cancer epidemiologist at the University of California, San Diego, and colleagues.
Lung cancer screening benefits patients when low-dose CT is used, but not when high-dose CT is used, because radiation from higher doses may cause as many cancers as are detected by screening. The Centers for Medicare & Medicaid Services require institutions to use low-dose techniques and participate in a dose registry to be reimbursed for lung cancer screening. The American College of Radiology recommends that lung cancer screening scans have a volume CT dose index (CTDIvol) of 3 mGy or lower and an effective dose (ED) of 1 millisieverts (mSv) or lower.
A prospective study of registry data
Dr. Demb and colleagues conducted a study to describe CT radiation doses for lung cancer screening in current practice and to identify the factors that explain variation in doses between institutions. They prospectively collected lung cancer screening examination dose metrics from 2016 to 2017 at U.S. institutions participating in the University of California, San Francisco, International Dose Registry. Eligible institutions performed a minimum of 24 lung cancer screening scans during the study period. At baseline, the investigators surveyed institutions about their characteristics (for example, how they perform and oversee CT). Dr. Demb and colleagues estimated mixed-effects linear and logistic regression models using forward variable selection. They conducted their analysis between 2018 and 2019.
The researchers chose four outcome measures. The first was mean CTDIvol, reflecting the average radiation dose per slice. The second was mean ED, reflecting the total dose received and estimated future cancer risk. The third was the proportion of CT scans using radiation doses above ACR benchmarks. The fourth was the proportion of CT scans using radiation doses above the 75th percentile of registry doses (CTDIvol greater than 2.7 mGy and ED greater than 1.4 mSv).
Institutional characteristics associated with radiation dose
Dr. Demb and colleagues collected data from 72 institutions about 12,529 patients undergoing CT scans for lung cancer screening. Approximately 58% of patients were men, and the patients’ median age was 65 years. The mean CTDIvol, adjusted for patient size, was 2.4 mGy. The mean ED for lung cancer screening, adjusted for chest diameter, was 1.2 mSv.
A total of 15 institutions (21%) had a median adjusted CTDIvol value higher than the ACR guideline, and 47 (65%) had a median adjusted ED higher than the ACR guideline. Approximately 18% of CT scans had a CTDIvol higher than guidelines, and 50% had an ED higher than ACR guidelines.
Institutions that permitted any radiologist to establish CT protocols had 44% higher mean CTDIvol and 27% higher mean ED, compared with institutions that restricted who could establish protocols. Institutions that permitted any radiologist to establish protocols also had higher odds of conducting examinations that exceeded ACR CTDIvol guidelines (odds ratio, 12.0) and of being in the 75th percentile of the registry CTDIvol (OR, 19.0) or ED (OR, 8.5) values.
In contrast, having lead radiologists establish CT protocols resulted in lower odds of using doses that exceeded ACR ED guidelines (OR, 0.01). Employing external, rather than internal, medical physicists was associated with increased odds of exceeding ACR CTDIvol guidelines (OR, 6.1). Having medical physicists establish protocols was associated with decreased odds of exceeding the 75th percentile of the registry CTDIvol (OR, 0.09) values. Institutions that updated protocols as needed, rather than annually, had 27% higher mean CTDIvol.
“Although we cannot establish causality in this observational study, our results suggest that considering these factors (for example, allowing only lead radiologists to establish protocols) could have a meaningful impact on dose, and could be important areas to develop interventions to optimize doses of CT protocols” the investigators wrote.
The Patient Centered Outcomes Research Institute and the National Institutes of Health supported this research. The authors reported no conflicts of interest.
SOURCE: Demb J et al. JAMA Intern Med. 2019 Sep 23. doi: 10.1001/jamainternmed.2019.3893.