Medical Applications of Physics

By: Laurie-Anne Vazquez 07/31/2015 2:23PM
Category: Everyday Physics

CREDIT: DAVIDE ANSELMI

When most people think of physics, they think of scientists in lab coats performing experiments at CERN or NASA. But physics isn’t limited to a lab: it’s applicable in many different industries and occupations, including medicine. From drug creation and testing to patient-friendly technologies, Medical Physics and Biomedical Physics are responsible for many features of modern medicine.

Medical Physics is a field that applies physics concepts, theories and methods to medicine and healthcare. A practitioner of medical physics is called a “Medical Physicist” and is in charge of maintaining and improving patient health and healthcare processes in 11 different areas:

1. Scientific problem solving
2. Dosimetry measurements
3. Patient safety/risk management
4. Occupational and public safety/risk management
5. Clinical medical device management
6. Clinical involvement
7. Development of service quality and cost-effectiveness
8. Expert consultancy
9. Education of healthcare professionals
10. Health technology assessment
11. Innovation

There are applications of physics in experimental medicine as well, and those fall under the discipline of “Biomedical Physics.” Many world-class universities have departments for both Medical and Biomedical Physics, as they are prime environments for cutting edge research.

CREDIT: X-ZAB

One of the most common applications of Medical Physics is in diagnostic and interventional radiology which includes x-rays, fluoroscopy, mammography, ultrasound, lasers, nuclear medicine, MRI, and many other applications. These things are all made possible due to the use of particle accelerators, which are used in hospitals for PET scans and conventional cancer radiotherapy with X-rays. In addition, accelerators can also be used for hadron therapy, a form of radiotherapy that uses beams of charged proton particles to penetrate tissue with little diffusion and deposit maximum energy in a focused area. Hadron therapy targets radiation directly at malignant tissue, like a tumor, rather than irradiating all of the body’s healthy tissue. Right now, only 40 hospitals use this kind of therapy because it’s so expensive, but it has helped more than 60,000 patients worldwide and is advancing every day.

Positron Emission Tomography -- or PET scans -- utilize particle physics to identify radioisotopes that decay via positron emission and use them as tracers within the body. Those tracers are mixed into a dye that, once run through a scanning machine, helps doctors measure blood flow, oxygen use, glucose metabolism, and other factors that determine how tissue and organs are working at the cellular level. X-rays work in a similar way by using high frequency electromagnetic waves to pass through muscle and tissue to generate 3D images of the body, and if they’re passed through an x-ray detector outside of the body they can also detect shadows that indicate abnormalities. X-rays are best used to detect abnormalities like bone fractures, tumors and other abnormal masses, pneumonia, calcifications, foreign objects, and dental problems -- all of which have all become easier to quickly detect and treat. X-rays have improved the quality of healthcare by replacing previous methods of more-invasive detection -- like probing, exploratory, and often unnecessary surgery -- could not.

Another physics-related advancement in medicine is the field of Nuclear Medicine, which uses gamma-emitting radiotracers for single-photon emission tomography, or SPECT scans. SPECT scans use a gamma camera to record images at a series of angles around the patient, then reconstruct them to produce 3D cross-sectioned images of organs and how they’re functioning in the body -- like showing how blood flows to your heart or which areas of your brain are more or less active. SPECT imaging uses radioactive isotopes that have longer half-lives than the ones used for PET scans, and are both more common and less expensive. SPECT scans are particularly adept at helping detect brain disorders like dementia, clogged blood vessels, seizures, epilepsy, and head injuries. They are also helpful in detecting heart problems such as clogged arteries and reduced pumping efficiency, as well as bone disorders like hidden fractures or tumors.

CREDIT: X-ZAB

Radiation therapy is another widely used medical application of physics, as seen in the Gamma Knife, CyberKnife, proton therapy, boron neutron capture therapy, and LASIK. Gamma Knife focuses 201 beams of radiation directly on malignant tissue, delivering a powerful treatment to a single point. Individually, the beams are too weak to damage healthy tissue, but when focused they are one of the most effective treatments for brain tumors in modern medicine. Like hadron therapy, Gamma Knife targets only cancerous tissue without harming healthy cells, making it a more accurate treatment option than traditional chemotherapy and radiation.

CyberKnife works in a similar way, where focused rays of radiation concentrate on each tumor, accurate to less than one millimeter, the size of a pinpoint. Proton therapy uses high-energy protons -- positively charged particles like hydrogen and oxygen -- to target and destroy cancer cells with 60% lower radiation doses than X-rays. Also similar to hadron therapy, the number of centers offering this treatment is small, but growing.

LASIK (Laser-Assisted In-Situ Keratomileusis) surgery, or vision correction laser surgery, involves a great deal of physics. The surgery is performed with an ultraviolet excimer laser, or a UV laser that used excited dimers -- excited, unstable molecules of an inert gas and a halogen, argon or fluorine. According to Physics Central:

With the argon and fluorine confined in a tube capped with mirrors, one of which allows some light to escape, the result is an intense UV laser beam. Excimer lasers, unlike the familiar ones in bar-code readers, are pulsed—they pack their output into short bursts about 10 nanoseconds long (10-8 sec). This pulsing makes it ideal for eye surgery, because the intense pulses vaporize tissues without heating the rest of the eye. The UV light is absorbed in a very thin layer of tissue, decomposing that tissue into a vapor of small molecules, which fly away from the surface in a tiny plume.

Because the lens of the eye is coated in fluid, little light can be refracted, so LASIK is required to reshape the cornea and provide better vision. LASIK surgery is becoming increasingly more common and improving its accuracy, with only 5% of patients experiencing adverse side effects.

DR. ELIOT SIEGEL. CREDIT: BALTIMORE VAMC

In short, physics is helping advance medical techniques and technologies every day, and is largely responsible for increasing both the efficacy and precision of healthcare around the world. Medical Physics is also a quickly growing field. It’s only a matter of time until physicists find ways of using new principles and theories to solve some of the biggest healthcare challenges in the world today. Who knows which diseases will be eradicated in the future because of physics. If modern medical technology is any indication, it may be all of them.

 

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Posted on: 07/31/15 2:23PM
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Laurie-Anne Vazquez
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#MakePhysicsHappen @fiatphysica

“Fiat Physica shall hand the steering wheel of scientific innovation to the public, allowing them to contribute to science, communication, and discovery directly.”

Szabolcs Marka

Chair of the Education and Public Outreach Committee, LIGO and Associate Professor of Physics, Columbia University
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