计算机断层扫描（CT）定义的骨骼肌肉低量（SM）是头颈部肿瘤（HNC）患者中的糟糕预后指标，与体重或营养状况无关。我们使用第二胸椎（T2）处的骨骼肌肉（SM）测量值来确定糖尿病-骨骼肌肉指数（SMI）的阈值，研究低T2-SMI对总生存期（OS）和放疗期间体重减轻的影响。包括新诊断的HNC患者，并进行了诊断性正电子发射断层扫描（PET-CT）或放疗计划CT扫描。在T2处分析骨骼肌肉（SM），并应用模型预测L3处的骨骼肌肉（SM）。通过预测测量值，按BMI和性别分层确定糖尿病-骨骼肌肉指数（SMI）的阈值。研究糖尿病和低T2-SMI对OS和放疗期间体重减轻的影响。共分析了361个扫描（84％男性，54％咽口部肿瘤）。发现糖尿病患者占49％，显示出较差的OS（p = 0.037）。T2-SMI截断值为：女性-74 cm2/m2 [曲线下面积（AUC）：0.89（95％CI 0.80-0.98）]，男性（BMI < 25）-63 cm2/m2 [AUC 0.93（95％CI 0.89-0.96）]，男性（BMI ≥ 25）-88 cm2/m2 [AUC 0.86（95％CI 0.78-0.93）]。T2-SMI类别的OS没有差异。T2-SMI最低四分位数< 63 cm2/m2的患者显示出较差的OS（p = 0.017）。放射治疗期间体重减轻较高的患者有：非糖尿病患者（6.2％vs 4.9％，p = 0.023）；较高T2-SMI（6.3％vs 4.9％，p = 0.014）和最高四分位数（3.6％vs 5.7％vs 7.2％，p < 0.001）。这些T2-SMI阈值有效评估HNC中的CT定义的糖尿病。有必要进一步评估其临床应用。© 2023年。作者。

Computed tomography (CT)-defined sarcopenia, as a measurement of low skeletal muscle (SM), is a poor prognostic indicator in patients with head and neck cancer (HNC), independent of weight or nutritional status. We used SM measures at the second thoracic vertebra (T2) to determine T2-SM index (SMI) thresholds for sarcopenia, and investigate the impact of low T2-SMI on overall survival (OS), and weight loss during radiotherapy (RT).Adult patients with newly diagnosed HNC with a diagnostic PET-CT or RT planning CT scan were included. SM was analysed at T2 and a model applied to predict SM at L3. T2-SMI thresholds for sarcopenia were established with predicted measures, stratified by BMI and sex. Impact of sarcopenia and low T2-SMI on OS and weight loss during RT was investigated.A total of 361 scans were analysed (84% males, 54% oropharynx tumours). Sarcopenia was found in 49%, demonstrating worse OS (p = 0.037). T2-SMI cutoff values were: females-74 cm2/m2 [area under the curve (AUC): 0.89 (95%CI 0.80-0.98)], males (BMI < 25)-63 cm2/m2 [AUC 0.93 (95%CI 0.89-0.96)], males (BMI ≥ 25)-88cm2/m2 [AUC 0.86 (95%CI 0.78-0.93)]. No difference in OS with T2-SMI categories. Lowest T2-SMI quartile of < 63 cm2/m2 demonstrated worse OS (p = 0.017). Weight loss during RT was higher in patients; who were not sarcopenic (6.2% vs 4.9%, p = 0.023); with higher T2-SMI (6.3% vs 4.9%, p = 0.014) and; in the highest quartiles (3.6% vs 5.7% vs 7.2%, p < 0.001).These T2-SMI thresholds are effective in assessing CT-defined sarcopenia in HNC. Further assessment of clinical application is warranted.© 2023. The Author(s).