About the Center Services and Programs Proton Therapy Visitor Information Ways to Give
Roberts Proton Therapy Center

About the Facility
What is Proton Therapy?
How Does Proton Therapy Work?
Targets for Proton Therapy
New Research
The Patient Experience
A Never-Ending Quest for New Knowledge
Future Collaborations


Architectural Renderings and Technology Images
Construction Photos
Cyclotron Arrives in Philadelphia
Collaborative Research Effort with U.S. Military

How Does Proton Therapy Work?

Listen to James Metz, MD, speak about The Future of Cancer Care

The cancer-seeking proton beam at the Roberts Proton Therapy Center begins inside a cyclotron, a machine that, at just slightly bigger than an SUV, weighs 220-tons – as much as a 747 jetliner. The cyclotron uses enormously powerful magnets to strip protons from the hydrogen atoms in water and accelerate them to higher and higher velocity around a circular path, like cars on a racetrack.

When the protons reach their top speed and highest energy, they're directed out of the cyclotron by other magnets into a beamline, an airless tube that runs for about the length of a football field. At various points along the beamline, the proton beam is channeled by other magnets into five treatment rooms, four of them equipped with a 90-ton gantry, a rotating steel structure that moves around the patient to aim the beam at any angle. (The fifth treatment room uses a "fixed beam," around which the patient is positioned as needed.) This extensive space – where as many as 200 patients will be treated each day once the center reaches full capacity — makes the Roberts Proton Therapy Center the largest such center in the world.

Inside the treatment room, in the "nozzle" where the proton beam exits the beamline, a device called a multileaf collimator precisely tunes the energy of the beam and actually shapes it to match the unique profile of the individual patient's tumor, so that the most effective dose can be delivered exactly where it's needed. The Roberts Proton Therapy Center will be the only proton therapy center in the world that uses the cutting-edge multileaf collimator to individually shape the proton beam to fit each patient's tumor.


appointment icon

Need an appointment? Request one online 24 hours/day, 7 days/week or call 800-789-PENN (7366) to speak to a referral counselor.



About Penn Medicine   Contact Us   Site Map   Privacy Statement   Legal Disclaimer   Terms of Use

Penn Medicine, Philadelphia, PA 800-789-PENN © 2016, The Trustees of the University of Pennsylvania space