Bases physiques, biologiques et cliniques de l’utilisation des ions légers en radiothérapie. Le projet EULIMA (European Light Ion Medical Accelerator)

Member of the Eulima Project Management Group, Service de Protonthérapie-Neutronthérapie, Cyclotron Biomédical, Centre Antoine-Lacassagne, 227 avenue de la Lanterne, 06200 Nice, France.

Résumé

Le contrôle local des cancers est la condition essentielle de leur guérison. La radiothérapie participe à 50 % des traitements mais ne réussit que dans 75 % des cas. Une plus grande précision et une meilleure efficacité biologique de l’irradiation peuvent améliorer ce taux de guérison. C’est le fait des particules plus lourdes que l’électron: les protons ont une grande sélectivité physique, les neutrons sont biologiquement plus efficaces. Les ions légers (Carbone, Oxygène, Néon) possèdent ces deux caractéristiques à la fois et peuvent, d’après les données préliminaires obtenues à Berkeley(USA), modifier profondément les résultats de la radiothérapie. Dans le cadre de son programme de Lutte contre le Cancer, la Communauté Economique Européenne participe au financement de l’étude de faisabilité d’un accélérateur d’ions légers destiné à une implantation hospitalière, le projet EULIMA (European Light Ion Medical Accelerator).

Abstract

Improving the efficiency of radiotherapy is a constant concern in oncology: more than half of the patients who contract cancer receive radiotherapy at some stage and if the trend of recent years were to continue, by the year 2000, one European in three would be affected by cancer at some time in his or her life, compared with one in four today. Use of charged particles in radiotherapy represents indisputable progress in localization of the dose delivered to tumour masses, thereby allowing reduction of dose received by adjacent healthy tissues. For example, protons improve the physical selectivity of the irradiation, i.e. the dose distribution. High-LET (Linear Energy Transfer) radiations produce different biological effects, decreasing the differences in radiosensitivity, and allowing radiation therapy to control radioresistant tumours. Fast neutrons represent the most known of these high-LET particles, but they suffer of a relatively poor physical selectivity. The two approaches (physical selectivity and biological advantages) are joined In by light ions (Carbon, Oxygen, Neon). Highly selective high-LET radiation therapy can be performed for radioresistant tumours without damage to healthy tissues, largely enhancing the therapeutic ratio for tumour lying in or close to critical structures such as the brain and spinal cord. Preliminary results obtained in Berkeley (USA) demonstrate an improved local control of unresectable, slowly growing tumours, confirming what could be extrapolated from proton and neutrontherapy. Furthermore, radioactive light Ion beams can be used to verify the accuracy of treatment planning by checking the range of the particle with a PET camera, and in the future for the treatment itself. In the framework of its programme "Europe against Cancer", the Commission of the European Communities participates in the funding of the EULIMA (European Light Ion Medical Accelerator) project feasibility study, aiming to design a hospital-based light ion therapy facility in Europe.