Advantage window v4

The muscle mass was determined using segmentation of CT scan on dedicated post-treatment station (Advantage Window v4.7; GE Healthcare). A pre-established attenuation threshold of −29 to +150 Hounsfield units was selected and MCSA—defined as the total lumbar MCSA (including the external and internal obliques, paraspinal, rectus abdominis, transversus abdominis and psoas muscles) measured on an axial section passing through the middle of L3—was segmented [16 (link)]. Figure 1 illustrates this muscle segmentation in two patients: one with high muscle mass and one with small muscle mass. The interobserver agreement of this measure, assessed in 30 subjects from the development population, was almost perfect: Lin's concordance correlation coefficient = 0.999 (0.998 to 1.0) (Supplementary data, Fig. S1).

All CT examinations were performed on one of the three Multi‐Detector CT machines in our radiology department: Lightspeed VCT®, Discovery CT®, and Revolution CT® (GE Healthcare, Milwaukee, WI, USA), according to a standardized protocol. CT imaging parameters were as follows: unenhanced acquisition, 120 kV voltage, filtered back projection (FBP) image reconstruction without iterative reconstruction, 1.25 mm contiguous reconstructed slice thickness, and soft filter kernel. Segmentations were performed with a dedicated post‐treatment station (Advantage Window v4.7; GE Healthcare, Buc, France). A pre‐established attenuation threshold (−29 to +150) HU was selected,¹⁷ and the CSMA—defined as the total muscle area (including the external and internal obliques, paraspinal, rectus abdominis, transversus abdominis, and psoas muscles) measured on an axial section through the middle of L3—was segmented semi‐automatically, as previously reported.²¹ CSMA was normalized for height² and reported as the SMI in cm²/m².¹⁷ MD was defined on the basis of the attenuation of CSMA at L3 and is expressed in Hounsfield units (HU) (Figure1).²²