gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

The second generation scanning proton gantry at PSI

Meeting Abstract

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  • E. Pedroni - Center for Proton Therapy, Paul Scherrer Institute, Villingen-PSI, Switzerland

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog159

doi: 10.3205/09ptcog159, urn:nbn:de:0183-09ptcog1594

Published: September 24, 2009

© 2009 Pedroni.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.



At PSI we are in the process of commissioning a new gantry, Gantry 2 (G2), a system with many improvements, based on the experience of using the 18 years old Gantry 1 (G1).

The main characteristics of the new G2 are the following:

  • Compact iso-centric layout
    The beam line layout of G2 has a diameter of about 8.4 m.
  • Longitude-latitude-like choice of beam incidence
    The gantry mechanics is rotated only on one side of the gantry from -30° to 180° (0° being the vertical beam from above). The freedom to deliver beam on the supine patient from any direction is achieved by rotating the patient table in the horizontal plane. This provides a good access to the patient table at any time on a fixed floor. We have in part fixed walls and a ceiling for mounting commercial devices like Vision-RT.
  • Use of an in-room sliding CT
    We plan to install a Siemens sliding CT within reach of the patient table, for in-room positioning and for acquiring 4d-images (for prior and post treatment QA of moving target treatments and for respiration gating setup).
  • Beam-eye-view (BEV) imaging simultaneous to the proton beam delivery
    We plan to take X-ray images from within the nozzle through a hole in the yoke of the 90° bending magnet. BEV images will be used for cross-checking the patient positioning with CT. We will investigate the use of X-rays simultaneously to the proton beam delivery in synchronization with respiration gating and we plan to use fluoroscopic imaging to guide the proton beam.
  • Optimized nozzle design
    The nozzle has been designed with minimal material in the beam, in order to keep the size of the scanning beam small at all energies (<3–4 mm sigma between 100–230 MeV). The nozzle can be moved longitudinally to reduce the air gap between nozzle and patient. We will have the option to mount collimators and compensators on the nozzle. We plan to simulate the scattering technique with a system designed for delivering intensity modulated proton therapy.
  • Double parallel scanning
    We have chosen an “upstream scanning” solution as with G1, but with magnetic scanning in both transverse directions. By a proper design of the shape of the last 90° bending magnet we achieve a parallel beam scanning for both sweeping directions. The parallel magnetic scanning shall be used in combination with the remote control of the patient table to be able to treat tumors of any size.
  • Advanced scanning techniques
    We plan to develop much faster beam scanning techniques, to be able to apply multiple target repainting. This implies a fast double magnetic scanning with speeds of 1 and 2 cm/ms and fast dynamic energy variations with the beam line and degrader before the gantry (100 ms for changes of 5 mm in proton range). We will also explore the potential of using the modulation of the beam intensity at the ion source for dose painting.