Lung Cancer Screening: Common Ground and Differences
LDCT refers to using 10–30% of the total radiation dose used in a standard non contrast CT scan. NLST used multi-detector CT scanners with an average estimated effective dose of 1.5 mSv average as compared to 5–7 mSv for standard CT. There has been a significant debate over adoption of LDCT as a screening tool. One of the major concerns is the risk of radiation induced cancer arising from LDCT itself and from subsequent imaging to work up the positive results. Regarding this issue, there was an important study that suggested that the risk of medical radiation exposure is considerably lower than the benefit of screening. Using the BEIR VII risk estimates, in an hypothetical screening scenario for an individual undergoing annual LDCT examination from age 55 to 74, the lifetime attributable risk (LAR) of lung cancer mortality resulting from radiation exposure is estimated to be 0.07% for males and 0.14% for females. To put this information in context, radiation exposure from natural and manmade sources can reach as high as 6.2 mSv per year and airline crew members are exposed to radiation levels as high as 2–6 mSv per year.
Since NLST, there have been continued improvements in LDCT technology and virtually all CT scanners in the United States can obtain LDCT scans at the doses used in the NLST or even lower. Ultra low dose CT scanners (ULDCT) techniques have been developed which deliver excellent images with less than 1 mSv exposure, which is comparable to radiation exposure by CXR. The efficacy of ULDCT was assessed in a study of 52 patients against traditional LDCT. ULDCT was found to have a true positive factor of 0.944 for nodules >4 mm in size, which is the current cut-off for reporting a positive result in screening cohort. Hence, with the continued technological advancements we can hope to achieve the same diagnostic accuracy with the least possible radiation exposure. These studies have been conducted in a population with normal BMI and the data needs to be extrapolated and validated in patients with higher BMIs as they comprise approximately more than one-third of current population of the USA.
Stepping Stones to Adoption of LDCT as a Screening Tool
LDCT refers to using 10–30% of the total radiation dose used in a standard non contrast CT scan. NLST used multi-detector CT scanners with an average estimated effective dose of 1.5 mSv average as compared to 5–7 mSv for standard CT. There has been a significant debate over adoption of LDCT as a screening tool. One of the major concerns is the risk of radiation induced cancer arising from LDCT itself and from subsequent imaging to work up the positive results. Regarding this issue, there was an important study that suggested that the risk of medical radiation exposure is considerably lower than the benefit of screening. Using the BEIR VII risk estimates, in an hypothetical screening scenario for an individual undergoing annual LDCT examination from age 55 to 74, the lifetime attributable risk (LAR) of lung cancer mortality resulting from radiation exposure is estimated to be 0.07% for males and 0.14% for females. To put this information in context, radiation exposure from natural and manmade sources can reach as high as 6.2 mSv per year and airline crew members are exposed to radiation levels as high as 2–6 mSv per year.
Since NLST, there have been continued improvements in LDCT technology and virtually all CT scanners in the United States can obtain LDCT scans at the doses used in the NLST or even lower. Ultra low dose CT scanners (ULDCT) techniques have been developed which deliver excellent images with less than 1 mSv exposure, which is comparable to radiation exposure by CXR. The efficacy of ULDCT was assessed in a study of 52 patients against traditional LDCT. ULDCT was found to have a true positive factor of 0.944 for nodules >4 mm in size, which is the current cut-off for reporting a positive result in screening cohort. Hence, with the continued technological advancements we can hope to achieve the same diagnostic accuracy with the least possible radiation exposure. These studies have been conducted in a population with normal BMI and the data needs to be extrapolated and validated in patients with higher BMIs as they comprise approximately more than one-third of current population of the USA.
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