Proton Therapy

What is Proton Therapy

Proton therapy is an advanced form of external radiation therapy that uses high-energy proton beams rather than traditional X-ray beams to irradiate a tumor. The protons are precisely aimed at cancerous cells, attack their DNA and induce their destruction. While X-rays are highly penetrating electromagnetic waves that deliver most of their dose before they reach the tumor and tend to affect surrounding healthy tissue, protons deposit most of their energy at a precise and measurable depth that can be perfectly tailored to the tumor location. The absorbed dose of protons increases gradually as it enters the body, suddenly rising to a peak when the protons are slowed down and stopped. This phenomenon is called the Bragg peak and allows to significantly reduce the negative effects on healthy tissue. With this inherent characteristic of protons, it is thus possible to control the radiation dose, to delimit the irradiated region, to identify and to treat the tumor with unmatched precision, efficiency and safety.

How does it work?

The best way to understand how proton therapy works is to look at the physics and engineering inside the proton accelerator, or the synchrotron, and the beam delivery system.

• The proton begins its journey at the ion source. Within fractions of a second, hydrogen atoms are separated into negatively charged electrons and positively charged protons.
• The protons are injected via a vacuum tube into a linear accelerator and in only a few microseconds, the protons’ energy reaches 7 million electron volts.
• Proton beams stay in the vacuum tube as they enter the synchrotron, where acceleration increases their energy to a total of 70 million to 250 million electron volts, enough to place them at any depth within the patient’s body.
• After leaving the synchrotron, the protons move through a beam-transport system comprised of a series of magnets that shape, focus and direct the proton beam to the appropriate treatment room.
• To ensure that each patient receives the prescribed treatment safely and efficiently, the facility is controlled by a network of computers and safety systems. The gantry can revolve 360 degrees, allowing the beam to be delivered at any angle.
• As protons come through the nozzle, a custom-made device (the aperture) shapes the beam of protons, and another custom-made device (the compensator) shapes the protons into three dimensions, delivering them to the depth of the tumor.
• At maximum energy, proton beam travels 125,000 miles per second, which is equivalent to the two-thirds the speed of light.
• From the hydrogen canister to the patient, a proton typically travels 313,000 miles.