Muscle mass was measured by the analysis of electronically stored computed tomography (CT) images obtained at diagnosis of NSCLC and 30 days before the start of afatinib. The CT image parameters included contrast enhanced or unenhanced, 5 mm slice thickness and 120 kVp. The third lumbar vertebra (L3), with both transverse processes visible, was chosen as the standard landmark because this correlates best with whole‐body muscle mass. 10 Total cross‐sectional skeletal muscle area in the L3 region was computed using OsiriX software (Lite version 12.0.1; Pixmeo). 11 The L3 region contains the psoas, paraspinal and abdominal wall muscles.

The structures of those specific muscles were quantified on the basis of pre‐established Hounsfield Unit (HU) range of −29 to 150 HU. 12 If other structures apart from those skeletal muscles were automatically marked, they were eliminated by manual corrections. Muscle area was normalized for height in meters squared (m2) and reported as the skeletal muscle index (SMI; cm2/m2). Sarcopenia was defined as an SMI of ≤38.5 cm2/m2 for women and ≤52.4 cm2/m2 for men based on previous study. 13 Patients were dichotomized into the sarcopenia and nonsarcopenia groups. All muscle measurements were performed by the same radiologist.

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