Astronomers’ research on celestial bodies may have an impact on the human
body.
Ohio State Univ. astronomers are working with medical physicists and
radiation oncologists to develop a potential new radiation treatment—one that
is intended to be tougher on tumors, but gentler on healthy tissue.
In studying how chemical elements emit and absorb radiation inside stars and
around black holes, the astronomers discovered that heavy metals such as iron
emit low-energy electrons when exposed to x-rays at specific energies.
Their discovery raises the possibility that implants made from certain heavy
elements could enable doctors to obliterate tumors with low-energy electrons,
while exposing healthy tissue to much less radiation than is possible today. Similar
implants could enhance medical diagnostic imaging.
At the International Symposium on Molecular Spectroscopy, Ohio State Univ.
senior research scientist Sultana Nahar will announce the team’s computer
simulations of the elements gold and platinum, and the design of a prototype
device that generates x-rays at key frequencies.
Their simulations suggest that hitting a single gold or platinum atom with a
small dose of x-rays at a narrow range of frequencies—equal to roughly one tenth
of the broad spectrum of x-ray radiation frequencies—produces a flood of more
than 20 low-energy electrons.
“As astronomers, we apply basic physics and chemistry to understand what’s
happening in stars. We’re very excited to apply the same knowledge to potentially
treat cancer,” Nahar said.
“We believe that nanoparticles embedded in tumors can absorb x-rays
efficiently at particular frequencies, resulting in electron ejections that can
kill malignant cells,” she continued. “From x-ray spectroscopy, we can predict
those energies and which atoms or molecules are likely to be most effective.”
Nahar and Anil Pradhan, professor of astronomy at Ohio State, discovered that
particular frequencies of x-rays cause the electrons in heavy metal atoms to
vibrate and break free from their orbits around the nucleus, creating what
amounts to an electrically charged gas, or plasma, around the atoms at the
nanometer scale.
They have thus dubbed their medical concept Resonant Nano-Plasma
Theranostics (RNPT)—the latter word a merger of “therapy” and “diagnostics.”
“From a basic physics point of view, the use of radiation in medicine is
highly indiscriminate,” Pradhan added. “Really, there has been no fundamental advance
in x-ray production since the 1890s, when Roentgen invented the x-ray tube,
which produces x-rays over a very wide range.”
No fundamental advance, that is, until now.
“Together with long-time collaborator and medical physicist Yan Yu from Thomas Jefferson
Univ. Medical
College, we’ve developed
the RNPT methodology, which we hope will have far-reaching consequences for x-ray
imaging and radiation therapy,” Pradhan said.
He explained why metals such as gold or platinum display this behavior, and
how hospitals can take advantage of it. The basic physics, he said, has been
well understood since the 1920s.
Physicists have long known that electrons orbit the nuclei of atoms at
different distances, some close to the nucleus and some farther away. When one
of the close-in electrons is lost, a far-out electron may drop in to take its
place, which releases energy. This is called the Auger effect, which was
discovered in 1922.
Often the energy is strong enough to kick out a second electron, called an
Auger electron. The same process could also result in the emission of light
particles, or photons, at specific energies or frequencies, the most prominent
of which are called K-alpha x-rays.
The astronomers believe that K-alpha x-ray frequencies kick the close-in
electrons out of heavy metal atoms such as platinum, causing many far-out
electrons to fall in, and many more electrons to be kicked out. These free
Auger electrons are low in energy but great in number, and could feasibly
bombard nearby malignant cells and shatter their DNA.
While typical therapeutic x-ray machines such as CT scanners generate
full-spectrum x-rays, hospitals could employ RNPT using only K-alpha x-rays,
which would greatly reduce a patient’s radiation exposure.
That’s the function of the proof-of-principle device that the team has
constructed. Though the working tabletop prototype needs to be further
developed, these first experiments show that the Auger effect can be used to deliver
specific frequencies of x-ray radiation to heavy metal nanoparticles embedded
in diseased tissue for imaging or therapy.
Gold and Platinum are only the first two elements that the team is studying
in detail for the application of the RNPT methodology. Both metals are safe to
use in the body. Platinum is already used in the chemotherapy drug cisplatin,
where it helps deliver the drug by binding to malignant DNA.
“This work could eventually lead to a combination of radiation therapy with
chemotherapy using platinum as the active agent,” Pradhan said.
Cancer therapy is new territory for the astronomers. Together with Yu, they
came upon the idea for RNPT when they were trying to understand the abundance
of different chemical elements inside stars.
Their goal at the time was to help astronomers understand what different stars
are made of, based on how radiation flows through them and emanates from them.
Astronomers already have several methods for doing this, but their results
vary widely. By simulating how different elements behave when exposed to the
radiation inside stars, Nahar and Pradhan hope to help astronomers determine
precisely what our sun is made of.
Even for a profession as mathematically rigorous as astronomy, Nahar and
Pradhan’s undertaking is staggeringly large. They must calculate how every
possible atom contained in a star will react to every possible wavelength of
energy. They rely on the Ohio
Supercomputer Center
for these calculations and simulations; in fact, their research team has ranked
among the biggest users of computational resources ever since the center’s
establishment more than two decades ago.
The simulations have started to pay off, in an astrophysical sense. They
have revealed that previous observations and calculations of chemical
abundances of the sun may in fact be off by as much as 50%.
Even more surprising to the astronomers were the results for simulating the
radiation absorption by heavy metal atoms, such as iron. Iron plays the
dominant role in controlling radiation flow through stars, but it is also
observed in some black hole environments, where K-alpha x-rays can be detected
from Earth.
“That’s when we realized that the implications went way beyond atomic
astrophysics,” Pradhan said. “X-rays are used all the time in radiation
treatments and imaging, and so are heavy metals—just not in this way. If we
could target heavy metal nanoparticles to certain sites in the body, x-ray
imaging and therapy could be more powerful, reduce radiation exposure, and be
much more precise.”
