Imaging analysis

High‐dose CT or low‐dose CT of PET/CT images were analysed by two researchers for the measurements of adipose and muscular tissues using Slice‐O‐Matic software V4.2 (Montreal, Quebec, Canada Tomovision), which enables specific tissue demarcation using the previously reported HU thresholds.

Skeletal muscle area was assessed from a single axial slice at the third lumbar (L3) level considering psoas, paraspinal, abdominal transverse rectum, internal, and external obliques muscles, because the skeletal muscle in this region has been shown to represent to the whole‐body tissue quantities. 27 To measure the SMA (cm²), CT HU thresholds ranged from −29 to 150 were considered. Subsequently, SMA was normalized for stature, as has been reported elsewhere 20 and was referred to as the L3 skeletal muscle index (L3 SMI, in cm²/m²).

For those cases for whom digital records of high‐dose CT were unavailable, low‐dose CT of PET/CT scans were used as reference to perform these measurements. This choice was taken due to the optimal reproducibility and agreement between low‐dose and high‐dose CT in adipose and muscular measurements in our experience (data not published).

As previously studied in DLBCL population, 27 , 28 to identify sarcopenia, we considered gender‐specific cut‐offs of SMI of 39 and 34.4 cm²/m² for female and 55 cm²/m² and 47.1 cm²/m² for male patients. Moreover, we calculated a specific threshold of SMI for our population applying receiver operator curve (ROC) analysis and we used it also for out analyses.