Journal of the ICRU Vol 9 No 1 (2009) Report 81 Oxford University Press
Preface As the health of society systematically improves, chronic diseases become an increasingly significant component of the health detriment in populations of advancing age. The personal and societal burdens of acute illness are overtaken by often subtle increases in persistent degradations in health that when integrated over the advancing age of the population result in chronic and expensive disease states. Osteoporosis is exactly such a disorder. Osteoporosis is a systemic skeletal disease characterized by decreased bone mass and micro-architectural deterioration of bone tissue resulting in an increase in bone fragility and susceptibility to fracture (see for example, Rheumatology 47, iv2– iv8, 2008, for a thorough discussion of the structural basis of bone strength). In such patients, the activity of the osteoblastic cells producing bone tissue does not compensate for that of the osteoclastic cells destroying bone tissue. Hence, the mineral content, primarily calcium, is reduced. The loss of bone density generates a decrease in bone strength resulting in a concomitant increase in susceptibility of fracture, particularly in hips, spine, and wrists. Osteoporosis may result from several medical conditions, but hormonal changes in post-menopausal women are by far the most common. It may also result from endocrine disorders or the intake of certain drugs such as thyroid or corticosteroid hormones. A core issue for the diagnosis and management of this condition is the very small difference between normal bone density and that density where fracture becomes likely. Moreover, the difference in density between normal bone and bone of decreased density when interventional therapy might be effective is even less distinguishable. A variety of techniques are available to determine and monitor bone density. By far the most common techniques are based upon the characteristic variation in xray or gamma-ray interactions per unit mass in bone. A radiographic image is often the first indication of the disease and leads to a more complex study such as dual energy x-ray bone densitometry. A newer less established technique uses the variation in the speed of sound in bone to estimate bone density. Despite decades of research and development, there remain several critical issues that require discussion, harmonization, and resolution. These issues include: (1) the fact that appropriate quantities and units to specify bone density remain poorly defined and incorrectly applied, (2) techniques for densitometry are not well standardized, (3) the inherent lack of reproducibility and measurement uncertainties require careful consideration and impact upon the
diagnosis and monitoring of the disease state, and (4) measurement techniques based on different modalities or, even for the same modality, the use of slightly different devices and analysis procedures generate results of varying agreement and precision. Cumulatively, these and related issues have hindered the wider applicability of bone densitometry as the most appropriate tool for disease management despite the apparent fact that it is the only widely available tool for diagnosis of this condition. It is for these reasons that the ICRU determined that a consensus report would advance the state of the art and the wider applicability of bone densitometry in the diagnosis and management of osteoporosis. “Quantitative Aspects of Bone Densitometry” continues the efforts of the ICRU to provide consensus seminal reports on the applications of radiation physics to medicine. The various techniques used in bone density determination utilize fundamental processes to observe and, in many cases, screen the disease state in populations – an approach similar to screening mammography, a subject of a forthcoming ICRU report, or chest radiography, the subject of ICRU Report 70 (2003). The present report is comprehensive, reviewing all major techniques, their measurement quantities and units, their density resolving power, their diagnostic strengths and weakness, and the medical context in which they are best applied. These are essential subjects as different techniques may be applicable and cost effective for absolute determination of osteoporosis rather than the monitoring of disease progression or response to therapy. Of critical importance is the recognition that the density difference between normal and advanced disease may only be a few percent and results may vary depending upon the anatomical target the bone being a very complex organ. The ICRU is pleased to recognize the efforts and contributions of the report chairman and co-chairman Drs. Kalender and Engelke and committee members Drs. Fuerst, Gluer, Laugier, and Shepherd. This is a challenging subject of intense medical interest. The report should be valuable to practioners, manufacturers, and members of the public health community. The ICRU also acknowledges the statistical advice of Dr. Ying Lu, University of California, San Francisco to the section on performance measures.
# International Commission on Radiation Units and Measurements 2009
Paul M. DeLuca Jr. Gordon F. Whitmore Andre´ Wambersie