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 influence of the fragment particles from carbon beam on an OpenPET detector as in-beam PET for heavy ion therapy

Meeting Abstract

  • F. Nishikido - National Institute of Radiological Sciences, Chiba, Japan
  • Y. Yazaki - National Institute of Radiological Sciences, Chiba, Japan
  • H. Osada - National Institute of Radiological Sciences, Chiba, Japan
  • N. Inadama - National Institute of Radiological Sciences, Chiba, Japan
  • T. Inaniwa - National Institute of Radiological Sciences, Chiba, Japan
  • S. Sato - National Institute of Radiological Sciences, Chiba, Japan
  • E. Yoshida - National Institute of Radiological Sciences, Chiba, Japan
  • T. Yamaya - National Institute of Radiological Sciences, Chiba, Japan
  • H. Murayama - National Institute of Radiological Sciences, Chiba, Japan

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog151

DOI: 10.3205/09ptcog151, URN: urn:nbn:de:0183-09ptcog1515

Published: September 24, 2009

© 2009 Nishikido et al.
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Outline

Text

Background: We have proposed the "OpenPET" geometry which consists of two detector rings separated axially. The OpenPET is suitable for use as in-beam PET in heavy ion therapy due to the open space between the separated detector rings as shown Figure 1 [Fig. 1]. Annihilation gamma rays from irradiated volumes enter obliquely into OpenPET detectors. Therefore, detectors which can measure depth of interaction (DOI) are required to reduce parallax error. Since the DOI detectors need to identify the large number of crystals in proportion to the number of depth layers, the crystal identification performance is possible to deteriorate under heavy ion irradiation. In this presentation, we report the results of experiments about the influences of heavy ion irradiation, especially fragment particles, on the OpenPET detectors.

Material and methods: The experiments were performed using carbon beam in the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Sciences. The energy and intensity of the carbon beam were 290MeV/u and 108–109 pps. Carbon ions entered to a water phantom through an ionization chamber used as a beam intensity monitor. All of the primary carbon ions were stopped in the water phantom. First, to compare the influences of fragment particles on various scintillation materials, same size crystals of BGO, LuAG, LYSO and YSO were irradiated by 3.0x108 pps carbon beam and measured with a single channel PMT. Next, the influence of fragment particles on the DOI detector was studied. The DOI detector which consisted of a 8x8x4 LGSO crystal array with the optimized reflector arrangement and a 64ch position sensitive PMT. The scintillator and the OpenPET detector were positioned 30cm apart from the backside of the water phantom at an angle of 30 degree. Figure 2 [Fig. 2] shows experimental setup.

Results: After heavy ion irradiation, all of the scintillators were activated due to incidence of the fragment particles from the water phantom. The activation of the scintillators is lead to increase of count rate and degraded the performance of the DOI detector. From the comparison of the results for the scintillators, the increase of count rate depends on the effective atomic numbers. We conclude that lutetium doped scintillators are suitable in terms of the activation and detector performances previously studied. The DOI detector positioned in the OpenPET geometry were also affected by the fragment particles even though it was not in the line of the primary beam. However, we obtained sufficient detector performance as a PET detector by optimizing to an environment of heavy ion irradiation.

Conclusion: We studied responses of the OpenPET detector under heavy ion therapy. The influences of the activation by the fragment particles were measured for the various scintillators (Figure 3 [Fig. 3]). We obtained sufficient detector performance as a PET detector by optimizing to the environment of heavy ion irradiation.