Indiana University Cyclotron Operation for Proton Therapy Facility*

Indiana University has designed and finished construction of the Midwest Proton Radiotherapy Institute (MPRI) [1] consisting of one treatment room with two fixed horizontal beam lines and two treatment rooms with isocentric gantries. The first treatment room has been operating since February 2004, while the first Gantry treatment room has been in use treating patients since April 2007. The proton therapy facility is based on the IUCF K220 separated sector cyclotron, which provides a fixed 208.4 ± 0.1MeV beam to the end user. Each treatment room is designed to set its own energy for treatments and to operate independently from the setup in adjacent rooms. This allows IUCF to deliver beam to Radiation Effect Research Program (RERP) [2] between patient treatments. In this paper we discuss the key design decisions that enabled IUCF to support multi-user operation and our operational experience delivering beam to a medical facility. IUCF FACILITY DESCRIPTION IUCF K220 cyclotron delivers constant energy beam to a 57m Trunk beam line, which can feed beam on demand to either one of the three treatment rooms (TS1, TS2 and TS3) or to RERP. When not in use, the proton beam is parked in the beam dump, which contains a Multi-Layer Faraday Cup (MLFC) to monitor and maintain beam energy out of the cyclotron at 208.4MeV. The general layout of the IUCF facility is shown in Fig.1. The first section of the Trunk Line has achromatic optics to compensate for position and momentum dispersion in the beam extracted from the cyclotron. This improves beam stability and alignment along the Trunk Line. The subsequent telescopic sections of the Trunk line generate the beam double focus condition for each Treatment room. A set of wire scanners monitor beam focusing conditions, while the beam position monitors distributed along the Trunk Line facilitate beam alignment. The beam focusing and alignment conditions are both important for optimal beam transmission into the treatment rooms. Beam is deflected into the treatment rooms and into the RERP beam lines using fast ferrite magnets with 3ms rise/fall time. Each treatment room has independent energy setup using a beryllium double wedge energy degrader. The double wedge geometry provides continuous energy adjustment that varies residual range in water from 4cm to 27cm with 1mm precision. Identical doubly achromatic Energy Selection (ES) beam lines transmit the degraded beam into the three treatment rooms. TS1 has two fixed horizontal treatment nozzle systems, while TS2 and TS3 are each equipped with a 360-degree iso-centric gantry manufactured by IBA[3]. The optics of the ES beam line is based on a double bend spectrometer to optimize momentum selection with an adjustable slit installed in the middle, and to minimize neutron background in the treatment rooms from the energy degrading process. The second bending magnet is cast into a concrete wall separating the treatment room from the Trunk Line beam corridor. The science research area includes the Low Energy Neutron Source (LENS) [4] and Radiation Effect Research beam lines. The LENS facility is based upon high intensity RFQ-DTL system that operates independently from the cyclotron. The Radiation effect program shares the cyclotron beam with MPRI clinic.