The Proton Therapy Center: a high-tech hub

The Proton Therapy Center is one of the three technical platforms in the Oncological Radiotherapy department at Institut Curie. The others are located in Paris and Orsay. The diversity of radiotherapy techniques offered makes the radiotherapy platform at Institut Curie one of the most comprehensive in Europe.

The center also has a team of professionals on hand, including radiophysicists, handlers, technicians, oncological radiotherapists and anesthesiologists. It is also a hot spot for progress in proton therapy. Since it was re-converted to treat patients, the center has continued to advance knowledge and techniques to optimize the use of protons, and from a more general standpoint: that of radiotherapy. Robotics, imaging, IT simulation, biology of radiation and software for anticipating the effect of rays are all available techniques that have contributed to the research conducted at the Proton Therapy Center.

The cyclotron, the isocentric arm and the treatment rooms are all keystones of the Proton Therapy Center.

The cyclotron: The proton source is located at the center of the acceleration chamber. After being ionized, the particles are accelerated by a high-frequency electric field. They are simultaneously subjected to a magnetic field that bends their trajectory and sends them back to the accelerating zone. The protons then follow a spiral trajectory, until they reach the edge of the machine. From this last trajectory, they are ejected from the accelerator with adequate energy, then guided and focused to their point of use to treat the tumor.

The accelerator at the center is an isochronous cyclotron made by the company IBA, with the following properties:

• Energy of protons extracted: 230 MeV
• Intensity of beam: 0.1 to 500 nano-Amps
• RF frequency: 106 Mhz
• Weight: Two parts, 110 metric tons each

The isocentric arm: Due to the magnetic rigidity of protons, the bending of their trajectory requires significant magnets.  The isocentric arm is a metallic structure measuring 10 m in diameter and weighing more than 100 metric tons. It moves the line of the beam 360° around the patient to deliver the rays in exactly the line required, with accuracy of 1/10^th degree, and is thus able to treat hitherto inaccessible tumors, particularly in children.

The three treatment rooms

Eye treatment room: In this room, dedicated to ophthalmological treatments, the patient is seated. The room is equipped with a fixed, horizontal proton beam line and a robotized chair, needed for treating eye tumors.

Cranial and intra-cranial treatment room: This room is equipped with a fixed, horizontal proton beam line as well as a robotized arm to place patients in a seated or reclining position, for treatment of intra-cranial tumors in children and adults.
 

Room with isocentric arm: this room is equipped with a mobile proton beam line thanks to an isocentric arm, and a robotized arm to properly position patients – adults or children – and to diversify the directions of the beam to reach tumors that are inaccessible by equipment from the other rooms.

Let’s not forget the specifics

• Beam conformation systems: the center has a mechanical workshop where collimators and compensators are built. These two accessories, personalized for each patient, are placed along the proton beam to conform deposit of the dose to the location of the tumor.
• Positioning to the closest millimeter required: the precision achievable by proton ballistics requires positioning to the closest millimeter. The solution implemented at the Proton Therapy Center uses beads implanted in the patient at the start of treatment. Then the exact resetting between the virtual patient used for scheduling (scan imaging and MRI) and the actual patient present in the treatment room is based on these markers and a robot with 6 degrees of freedom. For each positioning, lengthwise and sideways radiographic images are taken to locate the beads. A software program helps achieve the exact position required in one or two iterations.