# CT body composition and sarcopenia measurement

Source: https://onco.cc/technologies/ct-body-composition-sarcopenia/  
OnCo record `ct-body-composition-sarcopenia` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The staging CT scan every cancer patient already has can be measured for muscle and fat at the level of the third lumbar vertebra; low muscle predicts chemotherapy toxicity and shorter survival across cancers, and software now does the measuring automatically.

## Summary

What it measures. On a single axial CT slice at the third lumbar vertebra, muscle and fat are separated by their density in Hounsfield units. Skeletal muscle area divided by height squared gives the skeletal muscle index; mean muscle density gives myosteatosis (fat within muscle); and visceral and subcutaneous fat areas come from the same slice. Low muscle by sex-specific thresholds is called sarcopenia even when the patient is not thin, and obese patients with low muscle (sarcopenic obesity) have the worst outcomes.

Evidence. Prado and colleagues showed in 2008 (Lancet Oncology) that sarcopenic obesity in patients with lung and gastrointestinal cancers independently predicted survival and that muscle mass, not body surface area, tracked chemotherapy toxicity. Since then hundreds of studies have linked low muscle and low muscle density to complications after surgery, dose-limiting toxicity from chemotherapy and targeted drugs, and shorter survival in most solid tumours. Deep-learning tools now segment the slice in seconds, so the measurement can be produced for every staging scan without extra imaging or radiation.

Who should have it and what changes. It is not yet a guideline-mandated test, but the cachexia and nutrition guidelines already treat body composition as a core assessment, and it is the objective counterpart to nutrition screening questionnaires and hand-grip strength. A finding of sarcopenia should trigger dietitian referral, resistance exercise and, in frail older patients, a full geriatric assessment; some centres use it in surgical risk discussions and in choosing between regimens. Dosing chemotherapy by lean mass rather than body surface area is being tested, not yet standard. The cost is software and reporting time; the scan is free because it has already been done.

## Fields

- Kind: Technology
- Status: emerging
- Last checked: 2026-09-17
- Also known as: skeletal muscle index; L3 muscle area; CT sarcopenia; opportunistic body composition; myosteatosis
- Principle: Threshold-based or deep-learning segmentation of skeletal muscle, visceral and subcutaneous fat on an axial CT slice at L3, normalised to height and compared with sex-specific cut-offs to classify sarcopenia and myosteatosis.
- Since: 2008
- Strengths: No new scan, radiation or cost beyond software; Objective and prognostic across many cancers; Automated segmentation makes it scalable
- Limitations: Cut-offs vary between populations and studies; Prognostic, with little trial evidence yet that acting on it changes outcomes; Needs a CT that includes L3, so not available from chest-only scans

## Sources

- Lancet Oncology 2008: Prevalence and clinical implications of sarcopenic obesity in patients with solid tumours of the respiratory and gastrointestinal tracts: https://doi.org/10.1016/S1470-2045(08)70153-0

## Connected records

- technologies: [AI in radiology](https://onco.cc/technologies/radiology-ai-screening/), [Cachexia pharmacotherapy: GDF-15 blockade, anamorelin, olanzapine](https://onco.cc/technologies/cachexia-appetite-pharmacotherapy/), [CT (computed tomography)](https://onco.cc/technologies/ct/), [Enhanced recovery (ERAS) and perioperative nutrition](https://onco.cc/technologies/eras-perioperative-nutrition/), [Exercise & lifestyle oncology](https://onco.cc/technologies/exercise-oncology/), [G8 geriatric screening tool](https://onco.cc/technologies/g8-geriatric-screening/), [Geriatric assessment](https://onco.cc/technologies/geriatric-assessment/), [Nutrition support and cachexia management](https://onco.cc/technologies/oncology-nutrition/), [Oncology nutrition assessment and medical nutrition therapy](https://onco.cc/technologies/nutrition-screening-mnt/), [Quantitative imaging biomarkers (RECIST, PERCIST, SUV, ADC)](https://onco.cc/technologies/quantitative-imaging-biomarkers/), [Radiomics](https://onco.cc/technologies/radiomics/)
- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Gastric & gastro-oesophageal junction cancer](https://onco.cc/cancers/gastric/), [Head and neck squamous cell carcinoma](https://onco.cc/cancers/head-and-neck/), [Hepatocellular carcinoma](https://onco.cc/cancers/hcc/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Oesophageal and junctional adenocarcinoma](https://onco.cc/cancers/oesophageal-adenocarcinoma/), [Pancreatic ductal adenocarcinoma](https://onco.cc/cancers/pancreatic/)
- fronts: [Diet, Exercise & Lifestyle](https://onco.cc/fronts/nutrition-lifestyle/), [Imaging](https://onco.cc/fronts/imaging/), [Supportive Care & Survivorship](https://onco.cc/fronts/supportive-care/)
- terms: [Body composition (lean mass, fat mass, visceral fat)](https://onco.cc/terms/body-composition/), [Cancer cachexia](https://onco.cc/terms/cachexia/), [Dose reduction, interruption and discontinuation](https://onco.cc/terms/dose-modification/), [Malnutrition screening tools (MUST, NRS-2002, MST, PG-SGA)](https://onco.cc/terms/malnutrition-screening/), [Sarcopenia](https://onco.cc/terms/sarcopenia/)

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