The correlation of muscle quantity and quality between all vertebra levels and level L3, measured with CT: an exploratory study

Introduction: In patients with cancer, low muscle mass has been associated
with a higher risk of fatigue, poorer treatment outcomes, and mortality. To
determine body composition with computed tomography (CT), measuring the
muscle quantity at the level of lumbar 3 (L3) is suggested. However, in patients
with cancer, CT imaging of the L3 level is not always available. Thus far, little
is known about the extent to which other vertebra levels could be useful for
measuring muscle status. In this study, we aimed to assess the correlation of the
muscle quantity and quality between any vertebra level and L3 level in patients
with various tumor localizations.
Methods: Two hundred-twenty Positron Emission Tomography (PET)-CT images
of patients with four different tumor localizations were included: 1. head and
neck (n = 34), 2. esophagus (n = 45), 3. lung (n = 54), and 4. melanoma
(n = 87). From the whole body scan, 24 slices were used, i.e., one for each
vertebra level. Two examiners contoured the muscles independently. After
contouring, muscle quantity was estimated by calculating skeletal muscle area
(SMA) and skeletal muscle index (SMI). Muscle quality was assessed by calculating
muscle radiation attenuation (MRA). Pearson correlation coefficient was used to
determine whether the other vertebra levels correlate with L3 level.
Results: For SMA, strong correlations were found between C1–C3 and L3, and
C7–L5 and L3 (r = 0.72–0.95). For SMI, strong correlations were found between
the levels C1–C2, C7–T5, T7–L5, and L3 (r = 0.70–0.93), respectively. For MRA,
strong correlations were found between T1–L5 and L3 (r = 0.71–0.95).
Discussion: For muscle quantity, the correlations between the cervical, thoracic,
and lumbar levels are good, except for the cervical levels in patients with
esophageal cancer. For muscle quality, the correlations between the other levels
and L3 are good, except for the cervical levels in patients with melanoma. If
visualization of L3 on the CT scan is absent, the other thoracic and lumbar vertebra levels could serve as a proxy to measure muscle quantity and quality in
patients with head and neck, esophageal, lung cancer, and melanoma, whereas
the cervical levels may be less reliable as a proxy in some patient groups.