Series Physics and Medicine 1 Physics and medicine: a historical perspective Stephen F Keevil Nowadays, the term medical physics usually refers to the work of physicists employed in hospitals, who are concerned Lancet 2011; 379: 1517–24 mainly with medical applications of radiation, diagnostic imaging, and clinical measurement. This involvement in Published Online clinical work began barely 100 years ago, but the relation between physics and medicine has a much longer history. In April 18, 2012 this report, I have traced this history from the earliest recorded period, when physical agents such as heat and light DOI:10.1016/S0140- 6736(11)60282-1 began to be used to diagnose and treat disease. Later, great polymaths such as Leonardo da Vinci and Alhazen used See Comment pages 1463 physical principles to begin the quest to understand the function of the body. After the scientifi c revolution in the and 1464 17th century, early medical physicists developed a purely mechanistic approach to physiology, whereas others applied This is the fi rst in a Series of ideas derived from physics in an eff ort to comprehend the nature of life itself. These early investigations led directly fi ve papers about physics to the development of specialties such as electrophysiology, biomechanics, and ophthalmology. Physics-based medical and medicine technology developed rapidly during the 19th century, but it was the revolutionary discoveries about radiation and Department of Medical radioactivity at the end of the century that ushered in a new era of radiation-based medical diagnosis and treatment, Physics, Guy’s and St Thomas’ thereby giving rise to the modern medical physics profession. Subsequent developments in imaging in particular NHS Foundation Trust, London, UK (S F Keevil PhD); have revolutionised the practice of medicine. We now stand on the brink of a new revolution in post-genomic and Division of Imaging personalised medicine, with physics-based techniques again at the forefront. As before, these techniques are often Sciences and Biomedical the unpredictable fruits of earlier investment in basic physics research. Engineering, King’s College London, London, UK (S F Keevil) Introduction so arguably is the earliest example of diagnostic imaging. Correspondence to: Dr Stephen F Keevil, Department Medical physics, as we usually understand the term, By 200 AD, priests on the Greek island of Samothrace of Medical Physics, Rayne emerged as a distinct scientifi c discipline early in the were selling magnetic rings to treat arthritis,3 another Institute, St Thomas’ Hospital, 20th century in response to the growing use of ionising approach that has parallels nowadays, despite the absence London SE1 7EH, UK radiation in diagnosis and treatment. Establishment of of a convincing evidence base.4 [email protected] the fi rst posts for hospital-based physicists during this Some of the greatest thinkers of the medieval period period laid the foundations for a new health-care pro- worked at the interface between medicine and physics. fession, which continues to play an important part in the The Iraqi polymath Ibn al-Haytham (circa 965–1039), development and safe and eff ective implementation of usually known by the Latinised name Alhazen, physics-based technology. However, the relation between revolutionised the development of science and the physics and medicine has a much longer and richer scientifi c method in Europe and the Islamic world. history than this conventional picture suggests. In fact, Alhazen made particularly important contributions to medical physics could be anywhere between 100 and optics, including a description of the physics of vision, 5000 years old, depending on how broadly it is defi ned. and the fi rst experimental demonstration that sight is In this report, the fi rst in The Lancet Series, I have caused by rays of light entering the eye rather than by taken a broad view of how this relation has evolved, sometimes intentionally but perhaps more often by chance, across several centuries. It ends with a glimpse Key messages into the future, exploring how medical physics as a • The relation between physics and medicine dates back to the earliest recorded period profession and a scientifi c discipline might develop as of medical history. new areas of physics begin to be used by clinicians in • Across the centuries, application of physics laid the foundations for scientifi c the post-genomic world. exploration of the functions of the body. • Disciplines such as electrophysiology, biomechanics, and ophthalmology are the direct Antiquity and the middle ages result of the application of physics to medical and physiological questions. Physical techniques have been used in medicine from • Early in the 20th century, increasing use of radiation in medicine led to a demand for the earliest times. The Edwin Smith Surgical Papyrus, physicists who could apply their expertise directly to the clinical care of patients, and written in Egypt between 3000 and 2500 BC, is the oldest the modern medical physics profession began. known medical document. It contains a remarkable • Many advances in medicine, such as MRI and modern radiotherapy, are unpredictable description of the treatment of breast abscesses by spin-off s from fundamental physics research, and were only possible because of past 1 cauterisation with a fi re drill. A little later, the iconic investment in basic science. Greek physician Hippocrates (circa 460–377 BC) described • As we stand on the brink of a revolution in post-genomic personalised medicine, the fi rst recorded method for measurement of body once again physicists have the opportunity to play leading parts in the safe and 2 temperature. Hippocrates’ technique was actually a form eff ective use of new physics-based techniques for diagnosis and treatment. of thermal imaging akin to thermography (fi gure 1), and www.thelancet.com Vol 379 April 21, 2012 1517 Series Figure 1: Reproduction of Hippocratic thermography This image was taken 8 min after a cloth soaked in potter’s earth was applied to the volunteer’s back. The rate at which the cloth dries is related to the temperature of the skin underneath. The region on the right-hand side had previously been heated with a compress. Reproduced from Ostuka and Togawa,2 by permission of IOP Publishing. light emanating from the eye to probe objects as some had thought previously.5 Although Alhazen has been called the world’s fi rst true scientist,6 Leonardo da Vinci (1452–1519) has been described as the fi rst medical physicist because of his detailed studies of the mechanics of the human body.7 Although this work was more closely related to clinical engineering than to medical physics, the boundary between these disciplines is, at best, indistinct. His work on optics and his discovery of the principle of the contact lens fall squarely into the domain of physics,8 so perhaps we can add father of medical physics to the many epithets applied to Leonardo. Medical physics as iatrophysics The scientifi c revolution in the 17th century led to changes in the philosophy and practice of science although scholarly Figure 2: Giovanni Borelli’s representation of the body as a mechanism opinions diff er as to whether these changes were truly Reproduced from Maguet.12 revolutionary,9 or merely the logical outworking of ideas originating in the medieval period and earlier.10 However, René Descartes (1596–1650), in his revolutionary whether by radical or gradual change, by the end of the Traité de l’homme et de la formation du foetus (published period, scientifi c method had been established, science posthumously in 1675), described creatures as mech- and reason had supplanted religion as the principal source anisms, no diff erent from other material objects. In the of knowledge about the natural world, and the main case of human beings, the bodily mechanism was scientifi c disciplines had been established as spheres of directed by a rational soul located in the pineal gland.12 study distinct both from each other and from philosophy. But it was a simple step for later materialist philosophers, The recognition early in this period that material such as Thomas Hobbes (1588–1679), to dispense with objects obey rational physical laws led to the development the soul and so apparently reduce human beings and of mechanistic philosophy: the belief that nature could other animals to the status of automata.11 In the be exhaustively described in purely mechanistic terms. 17th century, the term for this school of thought was The case for extension of this new dogma to living iatrophysics (Greek iατρóς for a physician or surgeon), creatures seemed to be supported by discoveries about which is often translated as medical physics. But the role of the heart as a pump by Andreas Vesalius iatrophysics was a very diff erent enterprise from medical (1514–64) and the circulation of the blood by physics as we now understand it; iatrophysics was William Harvey (1578–1657), and later by the work of concerned with fundamental questions about the Anton van Leeuwenhoek (1632–1723) whose micro- function of the body and the nature of life, rather than scope opened up new vistas of biological structure.11 the practicalities of medical diagnosis and treatment. 1518 www.thelancet.com Vol 379 April 21, 2012 Series Iatrophysics provided useful insights into bodily function, leading to the development of biomechanics through the work of Giovanni Borelli (1608–1679) (fi gure 2).12 However, iatrophysics failed to explain many phenomena, most profoundly