Proton therapy at Institut Curie

What is proton therapy?

Proton therapy is an ultra-precise form of radiotherapy used to treat certain cancers in adults and children. The Institut Curie proton therapy center at the Orsay site in Essonne ranks third in the world in terms of the overall number of patients treated, and is the first in terms of the number of patients treated for ophthalmic tumors. Only three sites offer this therapeutic option in France: Orsay (Institut Curie), Nice, and Caen.

Unlike classic radiotherapy, which uses photon beams to irradiate and destroy cancer cells, proton therapy uses proton beams. Protons have two major advantages:

They pass through the body to deposit almost all their energy at a given depth (where the tumor is located), without going beyond. The tumor therefore receives a very significant peak of irradiation, while the healthy tissues located upstream and behind it are very little affected.
They follow a relatively straight trajectory and disperse little on the sides (low lateral diffusion). Therefore the healthy tissues located around the tumor are spared.

Thanks to this very precise and selective targeting of the tumor volume, proton therapy makes it possible to increase the dose delivered to the tumor, and thus to strengthen the effectiveness of the treatment, while preserving the adjacent healthy tissues.

Proton therapy is therefore a method of choice for treating radio-resistant tumors, which require higher doses of radiation, or those located near sensitive organs (optic nerve, brain, spinal cord, etc.). Moreover, due to a decrease in the integral dose – the total dose of irradiation received by the patient in the tumor but also in the rest of the body – this treatment is preferred in children, adolescents and young adults, who are most at risk of developing secondary radiation-induced cancers.

The reduction in exposure of healthy tissues to irradiation, enabled by proton therapy, significantly reduces the occurrence of side effects and the risk of complications. However, despite its ultra-precision, proton therapy can still induce in some cases side effects and complications identical to those of photon radiotherapy.

Indications for proton therapy

The recognized indications for proton therapy in France are tumors of the eye (melanomas of the choroid), chordomas, and chondrosarcomas of the head and spine (vertebral column), as well as pediatric tumors.

Since 2017, thanks to the implementation of a new proton therapy irradiation technique called PBS-IMPT (Pencil Beam Scanning - Intensity Modulated Proton Therapy or irradiation by intensity modulation), Institut Curie is able to perform craniospinal irradiation (at the level of the entire skull and the spinal cord) to treat tumors of the base of the skull such as medulloblastoma in children or adults, or certain brain tumors. To date, it is the only center in France to offer this type of irradiation. The PBS-IMPT also makes it possible to treat the thoracic localizations of Hodgkin's lymphomas in children and young adults, while sparing the organs at risk located nearby - such as the breasts. In young women, proton therapy thus limits the risk of radiation-induced secondary breast cancer.

Whether for adult or pediatric cancers, the therapeutic indications for proton therapy are broadening. Numerous clinical trials are underway to evaluate the benefits of proton therapy in new indications (lung, brain, ENT, breast, esophagus, pancreas, liver, etc.).

Curie expertise

The Institut Curie proton therapy center has three treatment rooms powered by the same particle accelerator (the cyclotron):

A room dedicated to the treatment of ophthalmic tumors: ocular or conjunctival tumors. Eye melanoma remains the cancer most frequently treated by proton therapy at Institut Curie.
A room dedicated to the treatment of head tumors (skull and brain)
A room equipped with a rotating arm (Gantry) allowing proton beams to be delivered all around the patient over the 360° radius and thus reaching tumors, which cannot be accessed with the equipment from the other rooms. All types of tumors can thus be treated in this room (skull, intracranial, orbit, thorax, abdomen, pelvis, spine, etc.). This room also makes it possible to improve the distribution of the dose delivered to the tumor thanks to the PBS technology (Pencil Beam Scanning), which entails scanning the entire volume of the tumor point by point using microbeams and varying their energy to reach different depths. Indeed, the tumor can have a complex shape, alternating concave and convex areas, and the depths targeted during scanning must follow the anatomy of the tumor volume. The IMPT (intensity modulation irradiation), an irradiation technique that complements the PBS, makes it possible to optimize these non-uniform dose distributions in depth for each treatment beam. Most pediatric tumors are treated in this room.

Proton therapy treatment

The proton therapy treatment is generally identical to that of photon radiotherapy. After an initial consultation with the radiation oncologist, a CT scan in the treatment position is carried out to perform contouring (3D reconstruction of the tumor volume to be irradiated) and dosimetry (distribution of the dose to be administered at the tumor area). In ophthalmology, a minor surgery under local or general anesthesia is required to place tantalum clips in the eye, which will serve as markers to precisely irradiate the tumor during proton therapy sessions.

At the start of each proton therapy session, the patient is repositioned in exactly the same way as during the preparation scan, using imaging. Restraint systems are also used to keep the patient still in the treatment position. Children under five are systematically anesthetized to make sure they remain still during the procedure.

Between 30 and 40 sessions of proton therapy are generally necessary for adult patients (and about 30 sessions for children), at the rate of one session per day, five times a week (Monday through Friday). It takes between 15 and 20 minutes for each proton therapy session (30 minutes for sleeping children). In ophthalmology, only four proton therapy sessions are required.

Proton therapy research

Institut Curie goes beyond routine care with its proton therapy research center that offers strong expertise in the area.

The cutting-edge research conducted at Institut Curie paves the way for innovative treatments in proton therapy. Mini-proton beam radiotherapy (pMBRT), based on spatial dose fractionation with alternating high and low dose regions, holds great promise for the treatment of radio-resistant tumors while enhancing protection of healthy tissues.

Flash radiotherapy, a radiotherapy technique, which was discovered in the laboratories of Institut Curie in 2014 and which entails administering a high dose of radiation (electrons or protons) in a fraction of a second, is also very promising.

In addition, several clinical research protocols in proton therapy are available to patients treated at Institut Curie for various cancers (meningiomas, esophagus).