Osirix version 3

Scans were coded in order to blind the researcher from outcome. Images were imported to Osirix® Version 3.3 (32-bit Pixmeo, Sarl, Switzerland). We selected a single image on the level of L3, with both transverse processes and delineated abdominal muscles by use of a semi-automated selection of region of interest. Psoas, quadratus lumborum, paraspinal, transverse abdominal, external oblique, internal oblique, and rectus abdominis muscles were included. The Hounsfield unit threshold range for skeletal muscle was − 29 to + 150. The images were manually corrected, if needed, by the propulsion and brush tools in Osirix©. The cross-sectional total muscle area at the level of L3 (cm2) was divided by the square of height (m2), which produced the skeletal muscle index (SMI). This method is suggested as the preferred method of measuring the muscle mass of cancer patients [25 (link)]. SMI limit for sarcopenia was < 52.4 cm2/m2 for men and < 38.5 cm2/m2 for women, based on a previous study by Prado et al. [26 (link)] For the survival and complication analyses, the preoperative SMI values were used, unless stated otherwise.
The process of delineating the abdominal muscle mass is shown in Fig. 1.Fig. 1

An example of SMI delineating. a Shows a male patient without sarcopenia (SMI = 57.6 cm2/m2), whereas b shows the same patient with sarcopenia (SMI = 47.9 cm2/m2) at follow-up