Neutrons for medicine

There are a lot of definitions of cancer: in a few words one could say that it represents a group of diseases characterized by the growth and uncontrolled diffusion of abnormal cells. Considering the number of deaths at the world level in 2005 (50 millions), cancer is responsible of 7.6 millions (that is 13%) with an expected increase to 11.4 millions in 2030. The innovations in the field of radiotherapy, chemotherapy, surgery and their combined applications have allowed to maintain these numbers under control. Radiation therapy has been used for the treatment of cancer and other diseases for approximately 100 years. As early as 1897, two years after the discovery by Wilhelm Conrad Rontgen, it was concluded that X-rays could be used for therapeutic as well as diagnostic purposes. But nearly 30 years were necessary to make radiotherapy world wide diffused: in fact, X-rays moved into clinical therapeutic routine only in the early 1920s. Since the first uses of radiation to treat cancer, important changes have been made in this field and several developments have been accomplished, both from the instrumental (new types of linear accelerators to generate higher energy radiation beams) and medical (different types of ionizing radiation and progress in treatment planning) points of view. On the other hand there is a series of tumours whose survival curve has not varied in time both in absolute and incremental terms: extended tumours (such as the ones of stomach, liver and lung), tumours localized near or in vital organs (such as the glioblastoma multiforme (GBM) in the brain), radioresistant tumours (such as melanoma). The research for new ways of treatment, together with the discovery of neutrons in 1932 and the studies concerning their properties, inspired in the American biophysicist G. L. Locher in 1936 the attempt to use neutron beams in radiotherapy in the so-called NCT (Neutron Capture Therapy) first and BNCT (Boron Neutron Capture Therapy) then. BNCT could (and the conditional is a must) represent a hope for all the cases still lacking a survival improvement. BNCT is a technique that in principle joins the localization capability of radiotherapy and the specificity of chemotherapy, allowing a selective release of the dose only to cancer cells, without damaging the surrounding healthy tissues. This technique is based on the irradiation with thermal and epithermal neutrons of a boronated compound (the so called carrier) selectively concentrated in tumor cells. Following the capture of a neutron, the 10B isotope emits high LET particles (an and a 7Li ion) that release their whole energy in the cell where the boron atom was present at the moment of the irradiation. The first BNCT experimental treatments were performed during the '50s. Since then, BNCT has met ups and downs in its history because of a physical and a biological reason: from the physical point of view, the features of the neutron beam (a flux >5 X 108 n cm-2 s-1 with an energy <10 keV) identify nuclear reactors as the only adequate sources; from the biological point of view, the carriers that bring the 10B inside the cell are not selective but exploit the greater metabolism of the cancer cells with respect to the healthy ones. BNCT has been performed in nuclear reactors in the United States (MIT, WSU), in Japan (KURRI, JRR-4), in Argentina (RA-6), in Europe (JRC - the Netherlands, Medical AB - Sweden, FiR1 - Finland) for activities of Phase I (toxicity) and of Phase II (ef_cacy); no center has started a Phase III protocol (BNCT tests randomized with respect to the standard techniques). Possible patients for BNCT treatments have to submit the request for the therapy to the International Ethic Committee who analyzes