According to a new study based on the International Early Lung Cancer Action Program (I-ELCAP), lung cancers identified in low-dose CT screening programs are similar to those identified by non- screening means. The research results, which were released on March 27 in Radiology, further alleviate concerns that cancers detected through low- dose CT screening are less aggressive than those found through other means, and therefore demand less attention and resources. In fact, the frequency of small-cell carcinoma and adenocarcinoma were similar for cancers detected through screening programs and outside the screening setting.
This study is another brick in the wall of evidence building for the value of low radiation dose CT lung cancer screening in high risk asymptomatic smokers. Regardless of whether nodules are solid or “ground glass” (non-solid), growth occurs that is similar in the screened populations and in those detected of having lung cancer due to symptoms.
While it is true we do not yet have a data-based analysis of costs versus quality life years saved, the evidence that screening is worthwhile continues to become stronger. “The CT scanners we have now are really phenomenal,” with resolution that continues to improve as the radiation dose falls, “so that the amount of information you can get out of them for emphysema, for coronary artery risks, and so on, continues to increase,” says Dr. Claudia Henschke, lead author of this study.
She goes on to point out that cancers detected via low dose CT screening “are real cancers that would kill you if they weren’t discovered early, so it kind of underscores again the data that we had shown in ELCAP and that NLST (National Lung Screening Trial) has shown — that screening for lung cancer saves lives.” And that is the key takeaway.
CT radiation dose has recently been in the limelight, not only in the news media but also for patients undergoing CT exams. Estimating CT dose is complex and further challenged by the different types of CT scanners available in the market today. In a recent study, investigators collected CT radiation dosemeasurement data from all the multi-detector CT (MDCT) scanners used in the National Lung Screening Trial. Radiation dose in CT is defined as CT Dose Index (CTDI). CTDI represents the average absorbed dose, along the length of the patient’s body from a series of contiguous scans. Normalized CTDI can be used to determine the efficiency of the CT scanner, and finally the dose imparted to patients. Normalized CTDI represents the dose per mAs (tube current x rotation time) where the mAs determines the number of x-ray photons utilized per rotation of the CT scanner.
The results of this study imply that one needs to be aware of the differences in normalized CTDI – not only between manufacturers, but also between models of CT scanners from the same manufacturer (Table 4 of this study).
This study showed that the average normalized CTDI varied greatly (by a factor of 2) across all scanners from different manufacturers. The dose efficiency of the CT scanners improves as the scanners get more complex, with the number of detectors along the length of the patient increasing from four or eight to sixteen and beyond (e.g.: 4- 8- or 16- slice CT scanner). This has an impact on image quality and patient dose because the more efficient the CT scanner, the less the dose to the patient to acquire the desired image quality.
The dose data in this study was collected for 96 MDCT scanners across 33 participating institutions. While the study did not focus on image quality and patient dose, it did examine scanner-specific radiation dose data across all institutions.