Fifty-seventh annual meeting of the American association of physicists in medicine
TH-EF-BRA-01: Patient-Size Specific Analysis of CT Doses From Lung Cancer Screening
The US Centers for Medicare & Medicaid Services (CMS) recently issued its final decision to approve the use of low dose CT for lung cancer screening and described some dose index requirements. The aim of this study is to evaluate CT dose indices from lung cancer screening taking into account patient size.
CT dose index data (CTDIvol, DLP) and patient size (height and weight) to calculate body mass index (BMI) were collected for lung cancer screening exams from Jan 1st to Dec 31th, 2014. All exams used Tube Current Modulation with identical Image Quality Reference parameter (Quality Reference mAs). X-ray dose management software was used to mine the data. CTDIvol and DLP values were analyzed based on patient's BMI classification. For a subset of patients, the average water equivalent diameter was estimated as well as Size Specific Dose Estimate (SSDE). All results were compared to the Medicare requirements (CTDIvol ≤ 3.0 mGy for a standard sized patient; appropriate reductions for smaller patients and increases for larger patients).
The dose indices over 351 patients were (mean ± SD): CTDIvol of 2.1 ± 0.7 mGy (min-max: 1.2 – 6.0 mGy); DLP of 75 ± 24 mGy*cm (min-max: 38 – 202 mGy*cm). The CTDIvol values by patient size (BMI) were 1.4 ± 0.2 mGy for underweight (BMI<18.5), 1.7 ± 0.3 mGy for normal weight (BMI of 18.5–24.9), 2.2 ± 0.4 mGy for overweight (BMI of 25.0– 29.9), and 2.9 ± 0.8 mGy for obese (BMI≥30.0). Approximately 9% of total patients had CTDIvol > 3.0 mGy; for each of these cases, the BMI was at least 27.0.
The scan protocol used resulted in CTDIvol values well within the Medicare requirements. Patients with larger BMI receive higher CTDIvol, but values > 3.0 mGy only occurred for overweight and obese patients.