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Physics and the life sciences

1st April 2013


Many of the greatest inventions in modern medicine were developed by physicists who imported technologies such as X rays, nuclear magnetic resonance, ultrasound, particle accelerators and radioisotope tagging and detection techniques into the medical domain. There they became magnetic resonance imaging (MRI), computerised tomography (CT) scanning, nuclear medicine, positron emission tomography (PET) scanning, and various radiotherapy treatment methods. These contributions have revolutionised medical techniques for imaging the human body and treating disease.

Now, in 2008, the American Association of Physicists in Medicine (AAPM), the premier scientific and professional association of medical physicists, is celebrating its 50th anniversary and is calling attention to the field of medical physics achievements

"There are a number of ways in which medical physicists contribute to medicine," says AAPM President Gerald A. White Jr. "Some develop cutting-edge technologies in the physics laboratory, while others are board-certified health professionals who apply these technologies in the clinic and help diagnose illness and alleviate suffering for millions of people a year in the United States."

As a practising medical physicist himself, White contributes to patient care at his practise at Colorado Associates in Medical Physics in Colorado Springs.

"Virtually all hospitals in the country today have medical physicists on staff to help administer radiation therapy treatment and to insure quality in both radiation treatment and imaging techniques," says long-time AAPM member Jean M. St. Germain, who is the Acting Chair of the Department of Medical Physics at Memorial Sloan-Kettering Cancer Center in New York.

In the coming year, the AAPM will be calling attention to the many ways in which medical physics has revolutionised medicine. A few highlights include:

1) USING PARTICLE ACCELERATORS TO DEFEAT CANCER

In the last 50 years, medical physicists have spearheaded the development and application of particle accelerators for cancer treatment. Once confined only to physics laboratories, linear accelerators are sophisticated high energy machines that can now deliver beams of energetic electrons or X rays to malignant tumours -- at doses capable of killing cancerous cells and stopping the tumour's growth.

In recent years, an advanced treatment technique called intensity-modulated radiation therapy (IMRT) has enhanced the ability of radiation to control tumours. IMRT uses computer programs to precisely shape the treatment field and control the accelerator beam in order to deliver a maximal dose of radiation to a tumour while minimising the doses to surrounding healthy tissues. IMRT is already in use for treating prostate cancer, cancers of the brain, head and neck and other malignant diseases, in children and in adults.

2) BETTER DETECTION OF BREAST CANCER

Techniques for breast imaging have undergone substantial advances since the introduction of the original film techniques. The early emulsion films were replaced with more sensitive film stocks and finally with digital imaging. As each of these newer techniques was introduced, doses to the patient were reduced and the sensitivity of the techniques for finding early and treatable disease increased. Computer-aided diagnosis and the use of MRI and CT for breast imaging promises to further advance cancer detection and treatment in the 21st century. MRI breast imaging is proving particularly useful at finding growths in younger women and at earlier stages.

3) MATTER/ANTIMATTER COLLISION IMAGING

Another rapidly growing technique used to detect diseases in people of all ages is positron emission tomography (PET). This technique uses short-lived radionuclides produced in cyclotrons. These nuclides are labelled to compounds such as glucose, testosterone and amino acids to monitor physiological factors including blood flow and glucose metabolism. These images can be crucial in detecting seizures, coronary heart disease and ischemia. In cancer care PET imaging is used to detect tumours and monitor the success of treatment courses as well as detecting early recurrent disease.

The actual imaging technique sounds like a science fiction movie -- it involves matter and antimatter annihilating one another. The short-lived radionuclides decay and emit particles known as positrons -- the antimatter equivalent to electrons. These positrons rapidly encounter electrons, collide, annihilate, and produce a pair of photons which move in opposite directions. These photons can be captured in special crystals and the images produced by computer techniques.

Other techniques, such as radioimmunoassay, use the decay of radioactive materials to study a variety of physiological conditions by imaging or chemical methods.

4) ENSURING THE SAFETY OF PEOPLE WHO GET CT SCANS

With the intent to promote the best medical imaging practises nationwide and help ensure the health and safety of the millions of people who undergo CT scanning each year in the United States, the AAPM issued a CT radiation dose management report in 2008, recommending standardised ways of reporting doses and educating users on the latest dose reduction technology. The report is available on the AAPM website at: http://www.aapm.org/pubs/reports/RPT_96.pdf. An associated news release can be accessed at http://www.aapm.org/announcements/AIPCTDoseReportNewsRelease.asp.

5) MEDICAL PHYSICS MOMENTS IN HISTORY

Some of the greatest medical advances in the history of medicine occurred in the past century and came from the minds and laboratories of physicists including:

* X rays
Discovered by Wilhelm Conrad Roentgen in 1895, the application of these rays to medical imaging was recognised and embraced immediately. When the Nobel Prizes were established at the turn of the century in 1901, Roentgen won the first prize (in physics) for his discovery of X rays.

* Magnetic Resonance
Though Felix Bloch and Edward M. Purcell shared the Nobel Prize in Physics in 1952, just a few years after discovering the phenomenon of magnetic resonance, it took a few more decades before their discovery led to the development of MRI, which is routinely used today to image the human body. In 2003, the Nobel Prize in Physiology or Medicine was awarded to Paul Lauterbur and Peter Mansfield for their work in MRI.

* Radioimmunoassays
In 1977, the Nobel Prize in Physiology or Medicine was awarded to AAPM member Rosalyn Yalow for her the development of radioimmunoassays, an extremely sensitive diagnostic technique that can quantify tiny amounts of biological substances in the body using radioactively-labelled materials.

* Computer-assisted tomography
In 1979, Allan M Cormack and Godfrey Newbold Hounsfield won the Nobel Prize in Physiology or Medicine for developing CT, which has revolutionised imaging because CT provides images with unprecedented clarity.





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