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

Evaluation of Absolute Doses in Spread-Out Bragg Peaks for Therapeutic Carbon Ion Beams

Meeting Abstract

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  • M. Sakama - Heavy Ion Medical Research Center, Gunma University, Showa, Maebashi, Gunma, Japan
  • T. Kanai - Heavy Ion Medical Research Center, Gunma University, Showa, Maebashi, Gunma, Japan
  • A. Fukumura - Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Showa, Maebashi, Gunma, Japan
  • Y. Kase - Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Showa, Maebashi, Gunma, 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. Doc09ptcog172

DOI: 10.3205/09ptcog172, URN: urn:nbn:de:0183-09ptcog1723

Published: September 24, 2009

© 2009 Sakama et al.
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Outline

Text

In particle therapy with the passive scattering methods, Spread-Out Bragg Peaks (SOBP) with the ridge or wheel filter was used to achieve the uniform biological effect for the irradiated tumor. Therefore there are the primary and fragment particles with variable energies in SOBP. In current dosimetry with SOBP, the air filled ionization chambers are used generally and the constant beam quality correction factor with the comparative large uncertainty in mono-energetic conditions is applied due to unknown physical parameters with the actual beam quality in SOBP. It is necessary to decide the absolute dose with high accuracy in the SOBP and validate the ionization chamber dosimetry. Calorimetry is the most direct dosimetry method due to the direct energy absorption measurement in principle. Absorbed dose in SOBP beams can be decided with small uncertainty by the dosimetry using the calorimeter positioned in SOBP region. Comparison of the calorimetry with the ionization chamber dosimetry make possible to sophisticate the dosimetry in SOBP beams.

We developed the portable graphite calorimeter in order to achieve the dosimetry including the heavy-ion beams. In the center of SOBP with 290 MeV/n carbon ion beam, absorbed dose was decided using the calorimeter with the graphite phantom. The ionization chamber dosimetry was performed in the same geometry and these comparisons were achieved. Two cylindrical chambers (PTW type 30001 and PTW type 30011, Farmer) and two plane-parallel chambers (PTW type 23343, Markus and PTW type 34001, Roos) calibrated by the absorbed dose to graphite and exposure to the 60Co photon beam were used. Similarly, the ionization chamber dosimetry was performed at the center of SOBP in the water phantom. Absorbed dose to graphite obtained by the calorimeter was converted to the dose to water using the ionization chamber method and Monte Carlo simulation.

In the center of SOBP 60 mm with 290 MeV/n carbon ion beam, the preliminary results of the comparisons to our calorimeter measurements revealed that, using the ionization chambers and the IAEA TRS 398, the absorbed dose comes out low by approximately 2%. Each factor of the beam quality correction factors in SOBP carbon ion beams is under investigation.