ONCOLOGY
The seca mBCA is the first and only device validated against the existing gold standards to ensure highly accurate assessment.
l Skinfold thickness measurement: This is the oldest of the listed methods. It is quick and inexpensive as it requires only a thickness caliper. The downside includes the intra-examiner and inter-examiner reliability and the assumption that the measured skinfold is representative of total body composition.
l Dual-energy X-ray absorptiometry (DXA): Developed to measure bone mineral density non-invasively, this method has become the gold standard for this body compartment and the diagnosis of osteopenia and osteoporosis. DXA is also used in the assessment of FM and FFM based on assumptions about body density. Those assumptions can be affected by several conditions which impair the measurement. Radiation exposure is low but nevertheless present in modern devices. DXA devices are expensive and require a specialised radiology technician.
l Magnetic resonance imaging (MRI) and magnetic resonance spectrography (MRS): A whole body MRI scan is the most accurate and therefore the gold standard method for SMM. The limitations are availability, the length of the procedure and the cost. As an alternative, specialists have used only a single MRI slide (level of the L4-L5 vertebrae), but the degree of accuracy suffers in comparison.
l Computed tomography (CT): The need to conduct several CT scans during diagnosis and treatment of cancer patients has raised the possibility of displaying and calculating body composition (SMM, FFM, FM). A single CT slice (level of the L3 vertebra) is analysed by a radiologist and special software. The limitations are the availability of the slice – especially in neck/head and breast cancers, the L3 region is not always included – and recent doubts about the accuracy of the prediction equations which calculate body composition of the entire body from a single slice. Like DXA, a CT scan exposes the patient to radiation.
l Ultrasonography of muscles (US): Efforts are being made to establish this method in intensive care to detect muscle wasting. It has not yet been used on cancer patients. Although the availability of this non-invasive test is exciting, the protocol to standardise each
measurement is quite long and complex. Furthermore, the examination should be performed by the same physician to lower the significant inter-examiner error. The list shows clearly the lack of an accurate, low-cost, easy-to-use bedside all-rounder. The BIA can address that lack.
l Bioelectrical impedance analysis (BIA): A mild current is passed through body tissue from the wrists to ankles to measure resistance and reactance. From this raw data, various formulas are used to calculate total body water (TBW), extra cellular water (ECW), FFM, FM and SMM. Validation of the BIA formulas is required.
A BIA device may be used in the medical field if its formulas have been validated for different patient populations against the specific gold standard method for each body compartment. That is, FFM and FM to the four-compartment model, TBW to deuterium dilution, ECW to sodium bromide dilution and SMM to MRI. The seca mBCA is the first and only device validated against the existing gold standards to ensure highly accurate assessment of every body compartment. In addition to making calculations, the device measures the phase angle. An indicator of cellular health, the phase angle is well-established in the scientific community as a prediction for outcome in various diseases and types of cancer. The measurement of hydration status can help to identify oedema caused by cancer or cancer treatment and the assessment of FFM, SMM and FM indicates nutritional and disease-related
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changes in body composition caused by diseases other than cancer.
Promising outlook for body composition and new anti-cancer drugs
New anti-cancer drugs such as monoclonal antibodies (mAB) have brought numerous benefits to patients but have also raised questions regarding the ethics of pricing the medications. Trastuzumab (Herceptin), an HER2 receptor antibody, for example, is indicated for HER2-positive breast and stomach cancer. The dosage of trastuzumab, calculated on the patient’s weight, depends on the chosen therapy regimen. One vial of trastuzumab containing 150 mg, the weekly dosage required by a 75-kg patient with breast cancer, costs the National Health Service £407. It may be that sufficient antineoplastic effects can be achieved with lower doses for some and higher doses for others. Resources in healthcare are limited. In light of the previously mentioned distrust of body weight and height as parameters, does it make sense to administer expensive anti-cancer drugs on the basis of weight alone? What is needed is a better parameter based on body composition in order to personalise therapy and use limited resources more intelligently.
Author
Michael Johannes Maisch, M.D. studied medicine in Giessen and worked for several years in OB/GYN and internal medicine near Hamburg, treating oncological patients. He joined Seca as medical advisor in 2016 and is now head of the Seca science centre, a scientific portal for body composition.
MARCH 2017
CSJ
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