Protontherapy

What is protontherapy?

It is an external radiotherapy which uses the energy of a proton beam to destroy tumor cells. Due to the physical properties of this beam, the radiation dose delivered to the tumor can be increased, while the dose delivered to the healthy tissues close to the tumor is minimized. A proton (part of the nucleus of an atom) has a positive charge and a weight, contrary to X-photons. It can therefore be directed precisely at its target thanks to magnetic lenses. It thus deposits its total energy at a determined depth corresponding to the tumor.

So-called classic radiotherapy uses several proton beams to treat a tumor. Here, a single proton beam can reach the tumor while sparing the healthy tissue located near it.

This form of radiotherapy makes it possible to deliver large doses to destroy radiation-resistant tumors close to sensitive organs, such as malignant intraocular tumors and tumors of the base of the skull and the spinal column.

In particular, it helps reduce the volume of healthy tissues crossed by the rays compared to photons, and in some clinical situations helps to reduce the risk of toxicity. It is a type of radiotherapy particularly suitable for radiation of some tumors in children and young adults.

The specifics of protontherapy at Institut Curie

The Protontherapy Center at Institut Curie started in 1991 by treating patients suffering from intraocular melanoma. The therapeutic indications spread rapidly to tumors at the base of the skull such as chordomas, chondrosarcomas, meningiomas and some encephalic tumors in children (craniopharyngiomas, ependymomas, germinomas, etc.).

Since 2006, with the development of procedures under general anesthesia, it has been possible to treat children under the age of six.

In 2013, the treatment of spinal-column tumors began, and in 2014, treatment of certain pelvic and abdominal tumors in children.

The center has a proton accelerator (Cyclotron), which delivers the beam in three treatment rooms:

• Two of the rooms are equipped with a fixed and horizontal beam line, enabling treatment only in sitting or reclining positions.
• One room is equipped with an isocentric arm, where the beam can rotate around the patient in the reclining position, and can thus treat all cases.

All the rooms are equipped with robots and an imaging system that allows for very precise patient positioning.

Thanks to the new system of active delivery of the beam, called PBS (Pencil Beam Scanning), installed in 2016, it is now possible to cover the tumor areas to be radiated point by point. The accuracy of this radiotherapy and, as a result, the sparing of healthy tissue on entry of the beam is improved.

This system is a first step on the way to intensity-modulated proton radiotherapy, which is one of the most sophisticated radiation systems for the conformation and protection of healthy tissues.

Protontherapy forms part of the radiotherapy arsenal offered by the Radiotherapy Oncology department of Institut Curie, the best-equipped center in France. Before a patient is referred for protontherapy, his/her case is discussed at multidisciplinary meetings (local, regional or national) in the presence of several specialists to confirm the indication and technical feasibility.