There is a
significant difference between standard (x-ray) radiation treatment and proton
therapy. If given in sufficient doses, x-ray radiation techniques will control
many cancers. But, because of the physician's inability to adequately conform
the irradiation pattern to the cancer, healthy tissues may receive a similar
dose and can be damaged. Consequently, a less- than-desired dose is frequently
used to reduce damage to healthy tissues and avoid unwanted side effects. The
power of protons is that higher doses of radiation can be used to control and
manage cancer while significantly reducing damage to healthy tissue and vital
organs.
Understanding how
protons work provides patients and physicians with an insight into this
mainstream treatment modality. Essentially, protons are a superior form of
radiation therapy. Fundamentally, all tissues are made up of molecules with
atoms as their building blocks. In the center of every atom is the nucleus.
Orbiting the nucleus of the atom are negatively charged electrons.
When energized
charged particles, such as protons or other forms of radiation, pass near
orbiting electrons, the positive charge of the protons attracts the negatively
charged electrons, pulling them out of their orbits. This is called ionization;
it changes the characteristics of the atom and consequentially the character of
the molecule within which the atom resides. This crucial change is the basis
for the beneficial aspects of all forms of radiation therapy. Because of
ionization, the radiation damages molecules within the cells, especially the
DNA or genetic material. Damaging the DNA destroys specific cell functions,
particularly the ability to divide or proliferate. Enzymes develop with the
cells and attempt to rebuild the injured areas of the DNA; however, if damage
from the radiation is too extensive, the enzymes fail to adequately repair the
injury. While both normal and cancerous cells go through this repair process, a
cancer cell's ability to repair molecular injury is frequently inferior. As a
result, cancer cells sustain more permanent damage and subsequent cell death
than occurs in the normal cell population. This permits selective destruction
of bad cells growing among good cells.
Both standard x-ray
therapy and proton beams work on the principle of selective cell
destruction. The major advantage of proton treatment over conventional
radiation, however, is that the energy distribution of protons can be directed
and deposited in tissue volumes designated by the physicians-in a
three-dimensional pattern from each beam used. This capability provides greater
control and precision and, therefore, superior management of treatment.
Radiation therapy requires that conventional x-rays be delivered into the body
in total doses sufficient to assure that enough ionization events occur to
damage all the cancer cells. The conventional x-rays lack of charge and mass,
however, results in most of their energy from a single conventional x-ray beam
being deposited in normal tissues near the body's surface, as well as
undesirable energy deposition beyond the cancer site. This undesirable pattern
of energy placement can result in unnecessary damage to healthy tissues, often
preventing physicians from using sufficient radiation to control the cancer.
Protons, on the
other hand, are energized to specific velocities. These energies determine how
deeply in the body protons will deposit their maximum energy. As the protons
move through the body, they slow down, causing increased interaction with
orbiting electrons.
Maximum interaction
with electrons occurs as the protons approach their targeted stopping point.
Thus, maximum energy is released within the designated cancer volume. The
surrounding healthy cells receive significantly less injury than the cells in
the designated volume.
As a result of
protons' dose-distribution characteristics, the radiation oncologist can
increase the dose to the tumor while reducing the dose to surrounding normal
tissues. This allows the dose to be increased beyond that which less-conformal
radiation will allow. The overall affects lead to the potential for fewer
harmful side effects, more direct impact on the tumor, and increased tumor
control."
The patient feels
nothing during treatment. The minimized normal-tissue injury results in the
potential for fewer effects following treatment, such as nausea, vomiting, or
diarrhea. The patients experiences a better quality of life during and after
proton treatment.
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