The use of
external beam radiation therapy is one of the most common forms of cancer treatments that a doctor or oncologist will recommend. This method involves radiotherapy equipment such as a
linear accelerator that aims radiation from outside of a patient’s body and directly targets local areas of a cancer site. Various types of cancers can be treated with external beam radiation therapy, and depending on the unique characteristics of the tumor, a selection of systems and treatments will be formed for the best outcome. Not only are there different types of machines that can be used, but also the radiation beam used in external radiation therapy can come from three kinds of particles called photons, protons, and electrons.
Photons
The majority of
radiation therapy machines use ionizing photon beams since they can reach tumors deep in the body. Photons are also used in x-rays, although they consume a much lower dose of the particle in comparison. The radiation that is delivered during photon treatment will damage the DNA of tumors and healthy cells alike. Radiation therapists aim to maximize the dose targeting the tumor while minimizing the radiation to nearby healthy tissues by creating different paths with multiple fields. To avoid overexposure to healthy cells, the treatment is generally given in stages over repeated scheduled sessions so that the healthy cells have time to repair.
Protons
Charged
particle radiotherapy is an alternative method of radiotherapy that uses beams
of protons or other positively charged particles such as helium, carbon, or
other ions that are not photons. These types of beams can also reach tumors
deep inside the body, but they perform differently than photons as they do not
scatter radiation on their path and will stop once they reach the targeted
tumor. Due to the physical characteristics of charged particles, it may be
possible to cover the tumor area with only one radiation field, creating an
advantage over the use of photons to spare more healthy tissues and cells.
Clinical trials are continuing to compare the usage of these two energy types.
There are cancer centers that are beginning to use proton beams in radiation
therapy, but they have higher costs and require a larger space to fit the
increased size of the equipment.
Electrons
Particles
with a negative charge are electrons. Electron beam radiation therapy is
designed to treat cancers like lymphoma and other tumors near the surface since
these electrons do not go deep into the body. These therapy options can be done
in two different ways:
- Spot treatment - This method is used for one or
more cancerous spots on the body that needs treatment.
- Total Skin Electron Beam Therapy (TSEB) - This
method is used when the entire surface of the skin needs to be treated. Other
treatments called compensation treatments can be part of the treatment plan to
guarantee that every area of the skin receives the proper dose required.
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