What is Proton Therapy?

Imagine a 196-ton, cancer-killing machine that can target a patient’s tumor with sub-millimeter precision while sparing nearby healthy tissues and minimizing side effects. In its most simple terms, that’s proton therapy.

Conventional radiation therapy has evolved and improved over the years and, if given in sufficient doses, will control many cancers. However, because X-ray beams are composed of primary photons and secondary electrons, they deposit their energy along the path of the beam, to the targeted tumor and beyond, thereby delivering radiation to healthy tissues before and after the tumor site.

The advantage of proton treatment is that a physician can predict and control where the proton releases the bulk of its cancer-fighting energy. As the protons move through the body, they slow down and interact with electrons, and release energy. The point where the highest energy release occurs is the “Bragg peak.” A physician can designate the Bragg peak’s location, causing the most damage to the targeted tumor cells. A proton beam conforms to the shape of a tumor with greater precision while sparing healthy tissues and organs.

How Does it Work?

The best way to understand how proton therapy works is to take a 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 shaping device called an aperture shapes the beam and another device called a compensator spreads the protons into three dimensions and conforms it to the depth of the tumor.
• At maximum energy, a 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.

Pencil Beam Proton Therapy

The team at MD Anderson Proton Therapy Center continues to expand ways to use proton therapy to benefit patients. The team pioneered pencil beam proton therapy, also called scanning beam, and is one of the few centers worldwide providing this innovative technology to our patients.

Pencil beam technology builds on the benefits of proton therapy. With a proton beam just millimeters wide, pencil beam combines precision and effectiveness, offering unmatched ability to treat a patient’s tumor without compromising quality of life – during and after treatment. Because pencil beam proton therapy is even more targeted, it results is even greater radiation dose directly to the tumor, shorter daily treatments and reduced side effects for patients.

Pencil beam is very effective in treating the most complex tumors, like those in the prostate, brain, base of the skull, and eye, and cancers in children, while leaving healthy tissue and other critical areas unharmed.

Is Proton Therapy Right for You?

Proton therapy benefits patients whose tumors are solid with defined borders, meaning the cancer has not spread to other parts of the body. The noninvasive treatment does not require surgery to remove the cancer, making it ideal for inoperable tumors. 

• Learn more about whether proton therapy is right for you