The fight against cancer, that is one of the most common disease in Europe, is carried on by three main arms: surgery, radiotherapy and chemotherapy. By combining these type of treatments, and by means of the improvement of diagnosis, physicians are now able to win about 45 % of the battles.The role of radiotherapy is firmly increasing especially when the tumour is primary, single, local and well defined. In these cases, in order to improve the so called "local control" it is mandatory to deliver high radiation doses to the target, the tumour volume, with the best sparing of the surrounding healthy tissues. This "Conformal radiotherapy" is currently carried on with photon beams - with up to ten crossing beams of X-rays – but also with "hadrontherapy", which uses directable beams of heavy charged particles (protons and ions) highly effective when the tumour is located close to vital organs which must not be irradiated.

The advantages of protons in radiotherapy are clearly illustrated in the right fig. where the dose distribution of various particles are compared. Protons and ions deliver the highest dose at the end of their path in tissue, avoiding totally to irradiate the more internal organs and sparing also the superficial tissues. It is possible therefore to achieve a highly conformal therapy with the use of even one or two beam ports, against the more than 4 of gamma rays. Carbon ions are even more effective to treat radioresistant tumours, due to their higher radiobiological effectiveness. The tumours more suited to hadrontherapy are those found at the base of the skull, in the back of the eye, and along the spinal chord. Moreover, pædiatric tumours, those of the central nervous system, of the prostate, of the liver, of the gastro-enteric apparatus and of the lungs can draw benefits from this type of treatment.

Proton and ion therapy is rapidly expanding in the western countries. At the end of 1998, 26000 patients were treated in several centres, in Europe, USA, Russia, Japan. After one decade of use of accelerators built for nuclear physics, many oncologycal centers (e.g. Mass. General Hospital, Loma Linda University Medical Center, Centre Lacassagne at Nice,…) prefer to install dedicated machines that now start to be even commercially available (e.g. Cyclone 235 by IBA).

In Italy a strong activity has been pursued by the TERA foundation, leaded by U. Amaldi, that promoted the use of hadrontherapy in Italy collecting a large number of scientists under the Hadrontherapy Collaboration for several years in nineties, and that is proposing the construction of a synchrotron (CNAO) for protons and carbon ions in the Milan area. Another initiative (CATANA) is being carried on by the INFN at LNS, where a superconducting cyclotron is in operation and it should provide protons for the eye melanoma treatment, sharing the beam with nuclear physics experiments.

In Rome, the TOP project (Terapia Oncologica con Protoni) has been launched by the National Institute of Health, ISS (Istituto Superiore di Sanità), with the aim of constructing a proton accelerator and manage it in cooperation with the Istituto Regina Elena, IRE, the largest oncological institution in Rome. ISS decided in 1995 to accept the ENEA proposal to build a linear accelerator, and in 1997 signed an agreement with ENEA to start the accelerator construction. The linac was chosen for its modularity, that allows to built it according to the flux of funding and getting out a working equipment from almost each construction phase, and for the large possibility of a technology transfer to industry, being the development of this accelerator, so rich in technological aspects quite similar to the electron linacs used in conventional radiotherapy.