How does proton therapy work?

Basic principles of therapeutic action

The basis of the therapeutic action of the proton therapy is the penetration of radiation energy into the tumor cell and the destruction of its DNA. This leads to the cessation of tumor cell division and the cessation of its growth.

Due to their physical properties, protons  move along a straight trajectory, and their radiation energy is not dissipated along the way. The mass of protons allows the doctors to precisely control their movement and stop the particle inside the tumor, at which point the proton releases the maximum amount of energy and destroys the tumor.

Unlike traditional radiation therapy, in which the X-ray beam does not stop in the tumor, but passes through, releasing energy along its entire path and irradiating the surrounding tissues, as a result of which the tumor receives less radiation energy, and healthy tissues are exposed to radiation.

In these images we see a comparison of the action of traditional radiation therapy (1) and proton therapy (2). In the former case, the beam passes through the human body and irradiates not only the tumor itself, but also the brain stem and neck organs.

The proton beam, on the contrary, stops at the location of the tumor and releases maximum energy at this point, has the maximum effect on the tumor and does not affect the brain stem and neck. 

How does a proton therapy machine work?

The design of a proton therapy machine is much more complex than the design of an accelerator used for traditional radiation therapy.

The machine in which the patient is placed during a proton therapy session is only the final element in a huge technological system that begins with a cyclotron and ends with a gantry – a device from which protons enter the patient’s body. The size of the system is comparable to a two-story house and it is located underground, under the building of the proton therapy center.

Hydrogen atoms are split into electrons and protons, after that the protons enter the cyclotron, where they are accelerated.
Then, the protons pass through a long energy selection system of, which allows the most accurate adjustment of the radiation dose.

At the final section of the chain – the gantry, the proton comes out and enters the patient’s body by a strictly pre-programmed trajectory.
The gantry has the ability to rotate 360° around the patient’s body, which allows the protons to be directed precisely to the target.

You can clearly see the process in this video: