How Does Proton Therapy Work?

Your proton therapy cancer treatment begins when each proton begins its journey at the injector located within an electric field. In the field, hydrogen atoms then separate into negatively charged electrons and positively charged protons. The protons travel through a vacuum tube within a pre-accelerator. This process boosts their energy to two million electron volts.

What is Proton Therapy?

The protons continue in the vacuum tube and begin their high-speed journey in the synchrotron. They travel around the synchrotron about 10 million times per second. Each time they circulate, a radiofrequency cavity within the ring delivers a boost of energy. This increases the protons' energy to between 70 and 250 million electron volts. The voltage achieved is enough to place them at any depth within the human body.

After leaving the synchrotron, the protons move through a beam transport system, continuing in the vacuum tube through a series of steering and focusing magnets that guide them to the four proton treatment rooms at the Loma Linda University Medical Center (LLUMC) Proton Treatment and Research Center.

Each proton treatment room has a beam delivery system, or nozzle, is the last device the protons travel through before entering the body. The nozzle shapes and spreads out the proton beam in three dimensions.

Radiation oncologists must determine location, shape, and tissue density of the target tumor before determining the number of protons to deliver. They must also calculate the depth that the protons must travel in order to calculate the speed and shape of the beam. These decisions render a beam that is highly accurate and practically ‘tailor made’ for a specific treatments. After leaving the nozzle, the protons enter the patient's body.

The equipment in the proton therapy treatment rooms vary based on the conditions treated. One proton treatment room has a stationary beam with two branches – one branch for irradiating eye tumors and the other for central nervous system tumors and tumors of the head and neck. The other three treatment rooms have gantries – wheels that are 35 feet in diameter that revolve around the patient to direct the beam exactly where needed. From the patient's perspective, all that is visible is a revolving, cone-shaped device. A fifth proton treatment room, used for beam calibration and basic research, contains three additional beam lines.

How Does Proton Therapy's Effectiveness Compare to IMRT or Other X-ray Treatments?

Because proton beams can be delivered in higher doses and with far more accuracy, proton therapy typically can control cancer with fewer treatments than IMRT. This pinpoint accuracy also results in fewer long-term side effects (since the radiation does not spill over and damage healthy tissue and organs) meaning that patients treated with proton therapy experience a higher post-treatment quality of life as compared to IMRT and even conventional x-ray treatments.

Is Proton Radiation Therapy Ever Combined?

Yes. Conformal proton therapy is often used in conjunction with X-ray therapy. This method boosts the dose to sites of gross disease and allows irradiation of a large tissue volume. Depending on the amount of cancer within a particular lymph node and type of cancer that is present, a patient may be at risk for harboring microscopic nests of cancer cells within the nodes. These nodes may lie at some distance from the primary tumor and may not be irradiated if conformal proton treatment alone is delivered to the tumor.

The objective of the treatment plan is to treat both the primary tumor and any areas where a microscopic tumor might hide. X-ray treatment alone will limit the total dose of radiation that can be given due to the high doses it delivers to large amounts of healthy tissue. Therefore, conformal proton radiation therapy is used to treat the primary tumor, and is then followed by X-ray therapy to treat the regional nodes. By giving some of the treatment with conformal protons, the total X-ray dose can be reduced substantially.

This reduces the risk of complications and permits treatment of potentially involved lymph nodes. Microscopic cancer within these nodes might be missed if X-rays were not used.

Read more to learn if proton therapy treatment is right for you.