Medical accelerator

How is vacuum involved in medical accelerators?

Making radiation therapy possible

January 27, 2023 | 4 MIN READ

Vacuum systems for medical accelerators

From the car that you drive to the food that you eat, vacuum technology plays a role in many parts of everyday life. One important field that vacuum technology is becoming more and more involved with is medical care, specifically cancer therapies.

In many cases, vacuum technology is indirectly involved, as it is used in the manufacturing process for various pieces of medical equipment. However, in the case of radiation therapy, vacuum plays a direct role; it is a key part of the function of the medical accelerators that make radiation therapy possible.

What is radiation therapy?

Radiation therapy is a type of cancer treatment that uses beams of intense energy to kill cancer cells. This is most often done using X-rays, but other types of energy can be used as well, such as protons and neutrons. This energy is usually delivered in the form of a beam generated from a machine outside the body. This is where a medical accelerator is used, as it generates this beam.

The high-energy beam is then focused on a very specific point on the body. Radiation therapy damages cells by destroying the genetic material inside the cell. Because both healthy and cancerous cells contain this genetic material, both are damaged during radiation therapy. Therefore, the goal is to destroy as many cancerous cells as possible while preserving healthy cells. 

Medical accelerators and types of energy beams

The design of the medical accelerator used to generate the energy needed for radiation therapy is an important part of preserving as many healthy cells as possible. The ability to focus the beam and control its energy are both important parts of targeting cancer cells.

Another important factor is the type of beam that is used. As mentioned earlier, X-rays are most commonly used, but other types of beams are becoming increasingly popular.

One example is the use of proton therapy, where a beam of protons is used instead of X-rays.

Because protons take quite a bit of energy to accelerate, the medical accelerators used for proton therapy are usually larger than other medical accelerators. They are usually cyclotron-style designs rather than the linear accelerators used to deliver beams composed of lighter particles, such as photons or electrons.

The main advantage of using a proton beam is that protons do not deliver radiation beyond a specific distance in the body. This is because protons only penetrate a certain distance into the body, which is dependent upon their energy. This relationship allows doctors to better control where the proton beams deliver their energy; therefore, it damages less healthy tissue.

Another type of beam that can be used is a neutron beam in a process that is called Boron Neutron Capture Therapy. This type of radiation therapy is a bit different, as it also requires a tumor-seeking drug that contains boron-10. When the patient is exposed to a low-energy beam of neutrons, many of the neutrons are absorbed by the boron-10.

This absorption creates a reaction that emits short-range, high-energy charged particles. These particles then destroy the surrounding tissue, which is composed of the cancerous tumor cells. This technique causes minimal damage to the surrounding healthy tissue. These new avenues of radiation therapy show that the medical community is getting better and better at destroying cancer cells while preserving healthy tissue. 

How is vacuum involved in radiation therapy?

Vacuum technology is an essential component of medical accelerators, as they need to be under high vacuum to operate. As discussed in a previous blog, high vacuum conditions limit beam-gas interactions, which can also be referred to as increasing the mean-free path of particles in the vacuum, such as protons and neutrons in the examples above.

If a proton or neutron beam was created in atmospheric pressure, it would only travel a matter of nanometers before it would be interrupted by air molecules. However, when the pressure is lowered to 10-5 mbar or lower, the protons and neutrons can travel much longer distances. This allows the beams to accelerate to the energy levels necessary for radiation therapy, where the beam can travel throughout the accelerator and be aimed at a precise place on a patient.

The typical pumps that are required for medical accelerator systems include:

  • roughing pumps, usually dry to reduce the chance of oil contamination
  • and turbomolecular pumps, which are needed to bring the pressure down to the necessary levels. In some cases, depending on the levels of radiation emitted from the accelerators, pumps with remote electronics are required.
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