Proton beam therapy enables a dose of high energy protons to be precisely targeted at a tumour, reducing the damage to surrounding healthy tissues and vital organs which is an advantage in certain groups of patients or where the cancer is close to a critical part of the body such as the spinal cord.
Proton therapy cancer treatment begins when each proton
begins its journey at the injector located within an electric field. In the
field, hydrogen atoms then separate into negatively charged electrons and positively
charged protons. The protons travel through a vacuum tube within a
pre-accelerator. This process boosts their energy to two million electron
volts. The protons continue in the vacuum tube and begin their high-speed
journey in the synchrotron. They travel around the synchrotron about 10 million
times per second. Each time they circulate, a radiofrequency cavity within the
ring delivers a boost of energy. This increases the protons' energy to between
70 and 250 million electron volts. The voltage achieved is enough to place them
at any depth within the human body.
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| Fig shows the superconducting Synchrotron and the Proton Beam Transport System |
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| Beam Transport System |
After leaving the synchrotron, the protons move through a beam transport system, continuing in the vacuum tube through a series of steering and focusing magnets that guide them to the proton treatment rooms. Each proton treatment room has a beam delivery system, or nozzle, is the last device the protons travel through before entering the body. The nozzle shapes and spreads out the proton beam in three dimensions.
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| Fig above shows Proton Magnet focus the beam and direct it into each treatment room. |
Radiation oncologists must determine location, shape, and
tissue density of the target tumor before determining the number of protons to
deliver. They must also calculate the depth that the protons must travel in
order to calculate the speed and shape of the beam. These decisions render a
beam that is highly accurate and practically ‘tailor made’ for a specific
treatments.
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| Treatment Gantry of a Proton Therapy System |
After leaving the nozzle, the protons enter the patient's
body.
The equipment in the proton therapy treatment rooms vary
based on the conditions treated. One proton treatment room may have a
stationary beam with two branches – one branch for irradiating eye tumors and
the other for central nervous system tumors and tumors of the head and neck.
The other treatment rooms may have gantries – wheels that are 35 feet in diameter
that revolve around the patient to direct the beam exactly where needed. From
the patient's perspective, all that is visible is a revolving, cone-shaped
device.
Proton beam therapy is only suitable for certain types of cancer, such as
highly complex brain, head and neck cancers and sarcomas as it does not lead to
better outcomes for many cancer cases than using high energy x-rays, which is
still considered the most appropriate and effective treatment for the majority
of cancers.Like high energy x-ray radiotherapy, proton beam therapy is painless, but patients may experience side effects similar to those experienced from other forms of radiotherapy.
How
Does Proton Therapy's Effectiveness Compare to IMRT or Other X-ray Treatments?
Because proton beams can be delivered in higher doses and
with far more accuracy, proton therapy typically can control cancer with fewer
treatments than IMRT. This pinpoint accuracy also results in fewer long-term
side effects (since the radiation does not spill over and damage healthy tissue
and organs) meaning that patients treated with proton therapy experience a
higher post-treatment quality of life as compared to IMRT and even conventional
x-ray treatments.
Is
Proton Radiation Therapy Ever Combined?
Yes. Conformal proton therapy is often used in conjunction with X-ray
therapy. This method boosts the dose to sites of gross disease and allows
irradiation of a large tissue volume. Depending on the amount of cancer within
a particular lymph node and type of cancer that is present, a patient may be at
risk for harboring microscopic nests of cancer cells within the nodes. These
nodes may lie at some distance from the primary tumor and may not be irradiated
if conformal proton treatment alone is delivered to the tumor.The objective of the treatment plan is to treat both the primary tumor and any areas where a microscopic tumor might hide. X-ray treatment alone will limit the total dose of radiation that can be given due to the high doses it delivers to large amounts of healthy tissue. Therefore, conformal proton radiation therapy is used to treat the primary tumor, and is then followed by X-ray therapy to treat the regional nodes. By giving some of the treatment with conformal protons, the total X-ray dose can be reduced substantially.
This reduces the risk of complications and permits treatment of potentially involved lymph nodes. Microscopic cancer within these nodes might be missed if X-rays were not used.
Side-Effect
Since proton therapy allows the radiation to unfold directly
in the tumour, the surrounding tissue and organs are protected to the best of
their ability. If a reaction – i. e. a side effect – occurs, only the
irradiated body region is usually affected. This can lead to irritation of the
skin or mucous membranes, which usually recede completely within two to three
weeks after treatment. Sometimes, however, a kind of permanent scarring can
also occur as a late consequence.
Information on this page is provided for interest only on a "best efforts" basis and does not
constitute personal advice. Always discuss medical conditions and related matters with your doctor.
Reference: https://protons.com/proton-advantage/how-does-proton-therapy-work
