External Radiation Treatment

What is External Beam Therapy?
How do we make external radiation?
The Linear accelerator is the life-blood of every department. Within its sleek frame, the machinery stars with an electron gun that produces particles. These particles are accelerated down a linear accelerator and hit a target. The collision produces invisible packets of energy called photons. These photons leave the machine in a precise way and travel in air. These photons enter the body as planned and become absorbed by the tissues. We have previously learned that one must use multiple angles of beams of radiation to preferentially deposit that radiation dose in the tumor while sparking normal organs.

What is 3D therapy?
We are always dealing in 3 dimensions for proper tumor targetting. The 3 points on the body help us line up the fields to the position of the body, and thus be highly accurate. We can usually not see the tumor with our direct vision, since most cancers are in organs deep within the body. Thus, we must use external markings to lead us to the correct location internally. This is a tedious process and requires great judgment of our therapy staff on a daily basis.

What is IMRT?
For at few years, we have been using a more advanced treatment technique called IMRT or Intesity Modulated Radiation Therapy. This technique is a much more dynamic approach and can, more accurately, tailor the treatment dosages to the multi-shaped cancer -bearing organs while avoiding the surrounding normal organs to the greatest degree possible. This is a more expensive and tedious process, and is only approved for prostate, head and neck and a few other sites. The insurance community has not universally recognized IMRT for treatment of several body sites, and thus we are limited in who we can use this treatment method for.

What is Image Guided Radiation Therapy (IGRT)?
In order to compensate for movement of internal organs that contain or are adjacent to tumors, and to more closely target tumors, we try and track the tumor during the course of radiation. We might have gold seeds implanted in the organ (see Prostate) or use landmarks that do not move during treatment. Thus on a daily basis, we have the ability to move our radiation fields to match the exact location of the tumor, and hopefully spare the surrounding normal organs better.

What is Electron Beam Therapy?
This technique uses the same machine as the above techniques, but uses the particles called electrons. These particles of radiation only penetrate a few centimeters into the tissue and are ideal for skin cancers and treatments that are very close to the skin surface.

The picture above (left) is our new linear accelerator. It works by generating its own radiation. It takes electrons and accelerates them at high energy until they strike a target. The resultant collision results in the production of invisible high energy radiation called photons. The picture (center) shows that the beam of radiation is bent and then shaped by leaves of metallic substance as seen in the third picture (above right). This beam can be shaped into multiple shapes as seen in the picture below.

IMRT is seen below when the radiation beam is pointed at the tumor from many directions, and the leaves that shape the beam dynamically move and mold the high dose of radiation into the needed ammunition to destroy the tumor and spare the surrounding structures. This is seen in a tumor around the eye (below left) and the lung ( below right).