Introduction to Medical Physics

Stephen Keevil, Renato Padovani, Slavik Tabakov, Tony Greener, Cornelius Lewis, Stephen Keevil, Renato Padovani, Slavik Tabakov, Tony Greener, Cornelius Lewis

• Publisher: CRC Press
• Year: 2022
• ISBN:
  9781498744829
• Edition: 1
• Topic: Medicina
• Subtopic: Biotecnologia in medicina

This textbook provides an accessible introduction to the basic principles of medical physics, the applications of medical physics equipment, and the role of a medical physicist in healthcare.

Introduction to Medical Physics is designed to support undergraduate and graduate students taking their first modules on a medical physics course, or as a dedicated book for specific modules such as medical imaging and radiotherapy. It is ideally suited for new teaching schemes such as Modernising Scientific Careers and will be invaluable for all medical physics students worldwide.

Key features:

• Written by an experienced and senior team of medical physicists from highly respected institutions

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• The first book written specifically to introduce medical physics to undergraduate and graduate physics students

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• Provides worked examples relevant to actual clinical situations

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1 Medical Physics, an Introduction

Perry Sprawls

Emory University, Atlanta, USA

DOI: 10.1201/9780429155758-1

Contents

1. 1.1 Introduction
2. 1.2 Medical Physicists
3. 1.3 Physics and Medicine
4. 1.4 The Diagnostic Process
5. 1.5 The Therapeutic Process
6. 1.6 Areas of Physics
7. 1.7 Ionising Radiation
8. 1.8 Medical Physics and Innovations in Technology
9. 1.9 Medical Imaging for Diagnosis
   • 1.9.1 The Discovery and the Beginning
   • 1.9.2 The Quest for Extended Visibility
   • 1.9.3 Imaging Methods or Modalities
10. 1.10 Radiation Therapy
    • 1.10.1 Treatment Planning and Requirement for Precision
    • 1.10.2 Radium and the Origin of Radiation Therapy
11. 1.11 Other Physics-Based Medical Applications
12. 1.12 Radiation Safety and Risk Management
13. 1.13 Conclusion

1.1 Introduction

Physics, along with biology, chemistry and psychology, is one of the basic sciences that are the foundation of medicine. Physics is especially significant because the human body is a physical environment and system. It is within the physical body that all of the other scientifically based functions take place producing and supporting life.

Medicine is the comprehensive science and practice of diagnosing, treating or preventing disease and other damage to the human body and mental system. This is usually achieved by interacting with the different scientifically based functions within the body. For example, infections are biological events and poison is a chemical condition. These would generally be diagnosed and treated based on those sciences.

Because the structure, composition and many functions of the human body are physical, physics is the basic science for the diagnosis and treatment of many conditions and is the foundation of the profession of medical physics.

1.2 Medical Physicists

Medical physicists are professionals with a strong academic background in general physics, medical physics topics and other medically related subjects including anatomy, physiology and pathology. They work in research and development, education and clinical medical physics. Clinical medical physicists generally have academic degrees in medical physics, supervised work experience (for example a residency programme in the US or the UK Scientist Training Programme (STP)), and are certified by regulatory bodies or professional organisations.

In addition to physicists, there are many other medical professionals, especially radiologists, radiographers and technologists, who apply physics in their clinical activities.

1.3 Physics and Medicine

An overview of the relation of physics to medicine is shown in Figure 1.1.

Figure 1.1 Overall relationship of physics to medicine.

The two types of medical procedures that are based on physics are diagnosis and therapy (treatment).

1.4 The Diagnostic Process

Diagnosis of diseases or injuries is usually a two-step process. The first step is obtaining information from the human body in the form of images that are produced by physical interactions within the body. The second step is the ‘reading of the image’ and interpreting or translating that information into a medical diagnosis. This last step is usually performed by qualified medical doctors, generally radiologists.

Physicists play a major role in the first step, designing and optimising imaging methods and procedures to capture the medically significant information from within the body while managing any potential risks to patients. This can be a complex process because images are physical objects with a number of important characteristics that can affect the visibility of objects and conditions within the body. It is the physicist who has the knowledge and experience required to analyse and adjust or optimise these factors for specific clinical procedures.

Clinical medical physicists are high-level professionals on the staff of hospitals and clinics. Their role is in assuring the diagnostic quality of imaging procedures and optimising procedures with respect to image quality and potential risks to patients. This is through several activities. One activity that is often required by government and accrediting regulations is the periodic evaluation of imaging equipment performance and image quality with specific testing procedures. Physicists use their knowledge and experience to consult and collaborate with the other medical imaging professionals, especially radiologists and technologists, in developing and optimising clinical procedures. Many medical physicists are educators, teaching medical physics students and physics residents, and also trainee radiologists who require knowledge of physics to qualify as radiologists.

1.5 The Therapeutic Process

There are several forms of therapy based on the application of various forms of physical energy to the body to treat and hopefully cure various diseases, injuries or other abnormal conditions. The use of ionising radiation is the medical specialty of radiation oncology or radiotherapy and is done by or under the direction of qualified medical professionals, generally physicians certified in that field.

Medical physicists play a significant role in therapeutic procedures using ionising radiation to treat cancer. The challenge and goal for each procedure is to maximise the radiation dose to the cancer tissues while minimising the radiation to the surrounding healthy tissues. This is achieved by the often complex process of treatment planning conducted by medical physics staff.

1.6 Areas of Physics

All areas of physics, ranging from mechanical to atomic and nuclear, have applications in both diagnostic and therapeutic procedures. Some are much more significant in modern medicine as will be described.

Atomic and nuclear physics is by far the foundation of most physics applications in medicine because this is both the source of several types of radiation and the basis of the interactions of radiation within the human body.

1.7 Ionising Radiation

Of special significance are ionising radiations, x-rays and radioactive substances, which can penetrate the human body and also produce biological effects when absorbed in tissue. Biological effects are the basis for radiation therapy to treat cancer but are generally undesirable in imaging applications. Medical physicists and the related profession of health physicists are scientists with knowledge and experience related to the exposure of humans to ionising radiation. Much of their work is in controlling and using radiation for the maximum benefit of humans.

Medical physics and the application of physics in medicine can be divided into four categories:

• medical imaging for medical diagnosis
• radiation therapy for treatment of cancer
• other physics-based medical applications
• radiation safety and risk management

The first two areas are where most medical physicists work and are often required by professional standards and legal regulations in clinical medicine activities.

1.8 Medical Physics and Innovations in Technology

The science of medical physics is closely related to developments and innovations in technology. Most physics activities involve equipment, and this is especially true for medical physics. Many of the advances in medical physics over the years have occurred and been made possible by developments in technology, especially computing and digital electronics. Most of the diagnostic imaging and treatment methods discussed later are based on physics interactions with the human body but are very much ‘high technology’. Therefore, medical physicists need up-to-date knowledge in technology along with physics.

1.9 Medical Imaging for Diagnosis

One of the greatest challenges in medical diagnosis, and where physicists have made major contributions, is in viewing the interior of the human body. Normal vision with light is generally limited to the surface of the body; so extending vision into the body requires radiation that can penetrate into and through the body. This is possible with radiations both below and above visible light in the electromagnetic spectrum, radio-frequency (RF) below and the ionising radiations above. It is these radiations and the associated physics that are the foundation of most modern imaging methods. The development of medical imaging has been an ongoing process for well over a century driven by physics discoveries and developments in technology. This includes digital and computer technology that is now a major component of all medical imaging methods.

1.9.1 The Discovery and the Beginning

Medical imaging, and to a great extent medical physics, had its origin in a physics laboratory at the University of Würzburg, Germany in 1895 when Professor Wilhelm Roentgen discovered a ‘new kind of rays’ to become known as x-radiation or Roentgen radiation. Following the discovery, he conducted extensive research to determine the properties of this radiation. This included the ability to penetrate objects and cast shadow images of internal structures and to display the images on both fluorescent screens and photographic plates. In early 1896, Dr. Roentgen gave a presentation in which he described the results of his res...