Objective: The study aimed to investigate the relationship between the ratio of lymph node attenuation to primary lesion attenuation on contrast-enhanced CT and the PET/CT standard uptake value (SUVmax) in head and neck squamous cell cancer (HNSCC).
Methods: Volunteers with advanced-stage, histopathologically proven HNSCC, indicated to have radiotherapy/chemoradiotherapy, were evaluated for CT and PET/CT for radiotherapy planning. The attenuation and SUVmax of the primary lesion and the largest, possibly metastatic lymph node, and the round index and volume of the lymph node were calculated. The relationship between lymph node/primary lesion attenuation and SUVmax ratios was investigated. The differences in CT findings between the SUVmax < and ≥3 groups were examined.
Results: Thirty-two cases with adequate diagnostic quality were studied. There was a very strong positive correlation between the primary lesion and lymph node attenuation (r=0.817, p<0.001), a strong correlation between the lymph node volume and SUVmax (r=0.681, p<0.001), and a moderate negative correlation between lymph node/primary lesion SUVmax and attenuation (r=-0.503, p=0.004). In patients with ≥3 SUVmax, lymph node volume and lymph node/primary lesion SUVmax were significantly higher, and the attenuation ratio was close to 1 (PPV 94.1, 86.3%, respectively).
Conclusion: In HNSCC, the lymph node/primary lesion attenuation ratio can be used instead of SUVmax if supported by other conventional CT findings. Metastasis should be considered if lymph node attenuation is similar to primary mass attenuation and excluded if higher. CT attenuation rate can be used as a supportive finding if PET/CT cannot be performed or lymph node SUVmax is close to the acceptable cut-off for metastasis.