The IBA proton therapy system selected by the Massachusetts General Hospital (MGH) to equip its new NPTC is presently under construction and test. This paper presents a progress report on the equipment construction. The cyclotron, as well as the rest of the equipment, are being progressively installed in the NPTC building. The acceptance tests of the whole system are foreseen for the end of 1997. I THE IBA TEAM AND THE NPTC PROJECTIn the early 1994, a team composed by IBA, SHI and GA, with IBA as the prime contractor, was selected by MGH to construct the proton therapy system to equip its new NPTC. The main elements composing this system are: a 235 MeV isochronous cyc1o;ron.-an energy selection system transforming the fixed energy beam extracted from the cyclotron into a variable energy beam (235 to 70 MeV range). a beam transport and switching system connecting the exit of the energy selection system to the entrance points of a number treatment rooms.two complete isocentric gantries fitted with a nozzle, and a system consisting of two horizontal beam lines, the large field one being equipped with a nozzle. a robotic patient positioning system. a global control system. a global safety management system independent of the global control system. This safety management system uses hardwired interlocks to achieve a safety level meeting applicable standards. I1 A CYCLOTRON-BASED SYSTEMOur goal was to meet all the clinical specifications of a state-of-the-art proton therapy facility in the most simple, reliable and cost effective way. This is the reason for our choice of a fixed energy cyclotron followed by an energy selection system. Figure 1: The 235 MeV cyclotron for proton therapy.With this choice, we have maintained and even increased the advantages of a fixed energy accelerator while completely eliminating the perceived disadvantages. Indeed, compared to the characteristic of a synchrotron which offers the possibility to vary the energy from pulse to pulse, our energy selection system allows for a comfortable 10% energy variation within 2 seconds, with the additional advantage that the high intensity, continuous beam extracted from the cyclotron can be intensity controlled from the ion source within 15 psec turn on/turn off time. These are essential features for the new treatment modes currently under consideration such as pencil beam scanning for example. I11 THE ENERGY SELECTION SYSTEM (ESS)The energy variability of the system is achieved by means of a carbon wedge used as an energy degrader. As a result of the energy degradation, there is an increase in emittance and energy spread. Emittance slits are therefore used to define the emittance of the transmitted beam, while an analysing magnet system limits the energy spread. Energy changes are completed in two seconds, using laminated magnets and quadrupoles. Figure 2 presents a picture of the energy degrader.
M. LACROIX~, A. NINANE~, G. RUCKEWAEF~, s. ZAREMBA~ 'Ion Beam Applications s.a. Chemin du cyclotron. 2 -1348 LOUVAIN-LA-NEUVE tCentre de Recherches du cyclotron -LOUVAIN-LA-NEUVE-Belgium CYCLONE 30 is a 30 MeV, H-cyclotron for radioisotope production, desbned for extremely high extracted beam intensity (500 pA) and low power consumption (less than 100 kW with a 15 kW extracted beam). The CYCLONE 30 prototype has now been operating for trvo years at LOUVAIN-LA-NEUVE and has achieved aU design goals while demonstrating very high reliabili!y. The mapr events in its development are reviewed. The data gathered so far Qive general basic trends for future designs : a 70 MeV, 2 mA machine desan study is presented. -Detailed design descriptions of CYCLONE 30 appear elsewhere [l], [2], [3] and are only summarized here (fig. 1). J 3 Q u d A General layout of CYCLONE 30CYCLONE 30 is a fixed field, fixed frequency, isochronous cyclotron designed to accelerate intense beams of H' ions up to a maximum energy of 30 MeV. The unusual magnet design combines the advantages of separated sector cyclotrons and solid pole cyclotrons. Energizing the cyclotron maanet requires as little as 7 kW. The magnetic field is adjusted during the manufacture by azimuthal shimming of the pole edges, providing a stable and highly isochronous field profile.The rf system consists of two dees connected at the centre and operating on the 4th harmonic of the particle revolution frequency. The half-wavelength resonators are entirely located in the magnet valleys. The total power needed to obtain the nominal 50 kV dee voltage is only 5.5 kW per dee. The final stage rf amplifier, a grounded orid triode capable of delivering 26 kW. is attached to the cyclotron structure and coupled to the dees through a capacitor.The negative hydrogen ions are produced by an extemal multicusp arc discharge ion source, biased at 29.5 kV. The axial injection system shown on fig. 2 includes two 15" bending magnets to select the appropriate beam species, a steering magnet, an electrostatic "EINZELL" lens, a beam stopper, a double gap rf buncher, a magnetic "GLASER" lens located in the cyclotron yoke and an electrostatic helicoidal inflector. m: The axial injection systemThe H-ions are extracted from the cyclotron by stripping through a thin carbon foil (40 mg/cm2). Continuously adjustable energy from 15 to 30 MeV is achieved by varying the radial position of the foil. Two beams may be extracted simultaneously at unrelated energies by means of two foils (one at each side).
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