Medical Physics

Medical physics is an interdisciplinary field that combines the health sciences with physics and engineering. It plays an integral role in modern healthcare, particularly in medical imaging and cancer therapy. Medical physics can be divided into four major categories: diagnostic, therapeutic, medical nuclear, and medical health physics.

Diagnostic medical physics involves the use of imaging modalities such as X-rays, fluoroscopy, computed tomography (CT), mammography, magnetic resonance imaging (MRI), and ultrasound. Medical physicists ensure that clinical imaging equipment functions optimally. They also assist other medical professionals in designing proper imaging procedures to achieve the best possible images at the tolerated level of patient exposure to radiation. A fundamental principle of radiological imaging is the minimization of radiation damage. A more detailed image is associated with higher patient exposure to radiation. Therefore, medical physicists must find the best compromise between image quality and the radiation exposure sustained by the patient.

Therapeutic medical physics deals with the accuracy of ionizing radiation delivery, which is utilized in cancer therapy. Therapeutic medical physicists work closely with radiation oncologists in designing treatment plans and performing quality assurance of equipment and procedures. They ensure that the radiation dose prescribed by the radiation oncologist is delivered to the desired location (the malignant tissue). Therapeutic radiation can be delivered either through external high-energy beams (usually electron or photon beams produced by a linear accelerator) or through internal radiation sources that are implanted into a patient. An ideal treatment irradiates the tumor while sparing the surrounding normal tissues and critical organs. This is difficult to accomplish in practice, but improved radiation [Page 1087]delivery techniques are gradually being developed to minimize the deleterious effects of radiation therapy on tissues adjacent to the tumor.

Nuclear medicine, unlike diagnostic or therapeutic medical physics, utilizes nonsealed (liquid, powder, etc.) radionuclides. These are applied for diagnostic imaging, such as the use of radioactive tracers, or for therapeutic applications such as thyroid ablation with iodine-131 in thyroid cancer patients.

Medical nuclear physicists have been instrumental in the development of novel instruments such as single photon emission computer tomography (SPECT) and positron emission tomography (PET), which are now standards of care.

Medical health physics investigates the effects of radioactivity on the human body and is applied in the design of proper treatment procedures as well as in the shielding of radiation facilities in order to protect healthcare workers and the public from excessive exposure. No amount of shielding can completely remove radiation, but it can bring it to an acceptably low level. Medical health physicists are employed by industries dealing with radiation, such as hospitals, nuclear power plants, and factories using radiation for sterilization.

Together, these subdisciplines of medical physics have significantly contributed to the diagnosis and/or treatment of many illnesses. Unfortunately, the imaging and therapy techniques that have been developed are quite expensive, and therefore, are not readily accessible even to the poor of the First World, let alone to the residents of the Third World.