Progress report on the construction of the Northeast Proton Therapy Center (NPTC) equipment

Abstract

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.

ATPF – a dedicated proton therapy facility

“…We propose to use two different gantries for the double-scattering and spot-scanning methods. The gantry associated with the double-scattering nozzle will be simple in structure but with a large scale, which to some extent is similar to the one designed by IBA [22]. It will leave a free space of at least 3.0 m from the last magnet to the iso-center.…”

`Riesenrad’ ion gantry for hadrontherapy: Part III

“…For hadrontherapy, gantries are impressive structures of the order of 10 m in diameter and 100 tons in weight and maintaining sub-millimetre precision for the transfer line elements supported by these structures is not trivial. To date, only proton gantries have been built and demonstrated to function satisfactorily [1,2,3].…”