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

Design and performance of an ionization chamber monitor for IBA proton treatment lines

Meeting Abstract

  • C. Brusasco - IBA, Louvain-La-Neuve, Belgium
  • J. Colin - LPC-ENSICAEN, CAEN, France
  • C. Courtois - LPC-ENSICAEN, CAEN, France
  • S. De Neuter - IBA, Louvain-La-Neuve, Belgium
  • J.-M. Fontbonne - LPC-ENSICAEN, CAEN, France
  • B. Marchand - IBA, Louvain-La-Neuve, Belgium
  • J. Perronnel - LPC-ENSICAEN, CAEN, France

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog025

doi: 10.3205/09ptcog025, urn:nbn:de:0183-09ptcog0256

Published: September 24, 2009

© 2009 Brusasco et al.
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.



The purpose of this study is the realization of an ionization chamber, called IC2/3, by the "Medical Applications" group of the "Laboratoire de Physique Corpusculaire de Caen" (LPC-Caen) in collaboration with IBA. This detector has been developed to be used as an on-line monitor for protontherapy dedicated irradiation head for Pencil Beam Scanning.

This device measures the beam position, the beam spot size, dose and dose rate delivered to the patient. The position and the spatial distribution of the scanned beam are measured by using horizontal and vertical strips. One of the main constraints is to reduce the angular straggling due to multiple scattering induced by the sensor in order to avoid degrading the beam spot properties. Therefore a particular effort has been done to make the detector as transparent as possible. For safety reason, the sensor is actually composed of two separate and redundant sensors called IC2 and IC3 in the IBA dedicated PBS Nozzle.

The first prototypes have been tested with proton beams at the "Westdeutsches Protontherapiezentrum Essen" (Essen, Germany). Proton beams of different energies were used to check the specifications requested by IBA. The dose rate can be measured with a relative uncertainty better than 1% for a beam current up to few nanoamperes. The spatial accuracy of the segmented sensors is better than 0.25mm. The low water equivalent thickness of the sensor leads to a scattering which does not exceed the tolerance on maximum scattering of 1.25mrad at the beam energy of 230MeV. The collection efficiency is better than 99.5% for a polarization voltage of 1200V.

Once permanently set in the PBS dedicated nozzle, this monitor will enable users to control the position, the spot shape, accumulated dose and the dose rate for each irradiation. IC2/3 is found to be well suited for quality assurance of protontherapy beams.