How Proton Therapy Works

Protons can be calibrated to release the bulk of their energy at certain depths inside the body and conform to the shape of the tumor. This level of precision helps us place more radiation dose exactly at the spot of the tumor, focusing more energy on destroying the cancer while sparing nearby healthy tissue.1

Northwestern Medicine Proton Center also has innovative technology like the vertical CT scanner and pencil beam scanning, which provide additional precision and allow care teams to treat a broader range of tumors and cancers with proton therapy.

What is Proton Therapy?
What is Proton Therapy? To learn more about other tumor types, visit our Video Library.

How Protons Deliver a Proper Dose of Radiation

Protons deliver a low dose to the healthy tissue then, at a precise depth, deliver a large burst of energy to the tumor. Shortly after this burst, they stop completely. To treat the entire tumor, additional protons are sent in at lower doses. In this way, protons completely irradiate the tumor while limiting the dose affecting the nearby healthy tissue.

Proton therapy image with a circle and the word cancer 

Is Proton Therapy New?

Proton therapy is not a new form of treatment, but it represents the latest advancement in radiation technology. The first patient received treatment with protons more than 50 years ago, and the Food and Drug Administration approved proton therapy as a radiation treatment option in 1988. To date, approximately 200,000 people worldwide have received proton therapy at centers in Europe, Asia and the United States.2

The Northwestern Medicine Proton Center is the 9th proton center to open in the United States and is the only proton center in Illinois. As of 2022, there are 39 proton centers in the United States.

The Proton Center is working to increase awareness of this treatment through academic presentations, papers and leadership within the medical community. Our mission is to make proton therapy accessible to everyone who needs it.

Read more frequently asked questions about proton therapy.

Important Milestones in the History of Proton Therapy Treatment

  • 1946: Physicist Robert Wilson first proposes that protons could be used to deliver an increased dose of radiation to a tumor while simultaneously decreasing the exposure of surrounding healthy tissue to radiation.
  • 1950: The first research trials are conducted on patients in Europe. Results are promising, but the inability of imaging technology to accurately "see" or locate many tumors and the inability to direct protons to sites deep within the body meant that only a few patients were appropriate candidates for the treatment.
  • 1970s: Imaging advancement, including computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET), allows physicians to "see" deep inside the body and precisely define the location, size and shape of tumors. This capability, coupled with improvements in proton technology, brought about today's growing interest in proton therapy as an important treatment option for cancer.
  • 1988: FDA approves proton therapy.
  • 1990: The first hospital-based proton treatment center in the United States was built in 1990 at Loma Linda University Medical Center in California.
  • 2010: The Proton Center opens, becoming the first facility in Illinois.
  • 2016: The Proton Center adds vertical CT scanning, providing patients with even greater precision and comfort during treatment.