Behind the Scenes of Proton Therapy

At the Emory Proton Therapy Center, the system generating proton therapy is entirely encased behind 14-foot thick concrete walls.

The Emory Proton Therapy Center is equipped with the most advanced and precise proton technology available anywhere and is supplied by Varian Medical Systems, Inc.

Traditional radiation therapy uses photons, which are X-ray waves, that can deposit some of their energy into tissues other than the tumor. Proton technology uses subatomic particles that accelerate and penetrate to very well defined tumor sites.


Proton therapy starts in the 90-ton superconducting cyclotron, which uses an alternating electrical field to accelerate a stream of protons to a high energy, enabling them to reach the depth of the tumor. Coming out of the cyclotron, the proton beam is traveling at about 100,000 miles per second.

Energy Selection System

The energy of the proton beam is adjusted to match the needs of each patient’s treatment based on the depth of the target.



The proton beam travels through a long vacuum tube, called the beamline, to reach each treatment room.  A series of magnets steer the proton beam and keep it focused.


Although not visible from inside the treatment room, each proton gantry is nearly 3 stories tall and weighs about 270 tons.  This structure enables the proton beam to rotate 360 degrees around the patient so that the proton beam can be directed from any direction required.

The proton gantry is equipped with low dose x-ray panels that can also acquire cone-beam CT scans to ensure you are in the proper position and the proton beam is aimed correctly prior to treatment delivery.

Treatment Delivery

Pencil beam scanning is used in every treatment room.  A narrow stream of protons is steered by a magnet to “paint” the radiation to match the size, shape, and depth of the target.  This allows for “intensity-modulated proton therapy,” for maximum flexibility in treatment planning and sparing of normal tissues.

Georgia Proton Treatment Center (GPTC), LLC, owns the building and the land and is financing the operations of the Emory Proton Therapy Center. GPTC is owned by Provident Resources Group Inc., a non-profit organization.

Advanced Technology

At the Emory Proton Therapy Center, we use additional advanced technologies to ensure the highest quality proton therapy treatments, including:

  • Dual energy CT simulator onsite for better image quality in treatment planning
  • A 1.5 T MRI onsite to better identify the target for radiation and normal tissues, and for monitoring response to treatment when appropriate. MRIs for diagnostic interpretation may also be obtained at the center when appropriate
  • Monte Carlo dose calculations and robust optimization to develop the most accurate treatment plans possible
  • For tumors that move with breathing (some lung and abdominal tumors), SDX voluntary breath hold is available to trigger the proton beam on and off when the tumor is in the right location, treating the smallest area of normal tissues
  • Ultrasound-guided placement of prostate fiducial markers and hydrogel rectal spacer (in appropriate patients) to further reduce radiation dose to the rectum
  • Continuous system monitoring, interlocks, safety checks, and rigorous quality assurance to ensure the most accurate treatment delivery

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