Assessment of Lean Body Mass Using Whole-Body Low- Dose CT From Pet/CT to Identify Cancer Cachexia

Introduction: Cancer cachexia is a multifactorial syndrome characterised by involuntary weight loss and muscle wasting, commonly seen in patients with advanced malignancies. Lean body mass assessment is crucial for the early indentification and monitoring of cancer cachexia. Dual-energy X-ray absorptiometry (DEXA) is widely accepted as the gold standard for evaluating body composition. This study aims to develop a method for estimating lean body mass using whole-body low-dose CT acquired during PET/CT imaging. Methods A cohort of patients enrolled in a prospective pilot study on cancer cachexia were included in the analysis. All patients underwent both DEXA and [ ¹⁸ F]FDG PET/CT imaging. Lean body mass was assessed by calculating the Total Body Lean Mass ratio (TBLMr) from DEXA (TBLMr _DEXA ) and also whole-body low-dose CT (TBLMr _CT ). Results A total of 33 (13-cachectic, 19-non-cachectic) patients with advanced malignancies were included in the analysis. The TBLMr _CT and TBLMr _DEXA were highly correlated (R ²  = 0.92). Bland-Altman plots indicated a scaling bias with increasing TBLMr _DEXA values, with the non-cachectic group exhibiting a tighter distribution (0.06 ± 0.05) compared to the cachectic group (0.03 ± 0.11). TBLMr values were significantly different between cachectic and non-cachectic groups for both the DEXA-derived (p < 0.004) and low-dose CT-derived (p < 0.010) measurements. Conclusion Whole-body low-dose CT obtained from routine [ ¹⁸ F]FDG PET/CT imaging can provide an accurate estimate of lean body mass, showing high concordance with DEXA-derived measurements and clinical diagnosis of cachexia. This method offers a practical method for monitoring cancer cachexia in patients undergoing routine [ ¹⁸ F]FDG PET/CT scans.