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

Fiber optic scintillator for high resolution dosimetry system of low energy proton beam

Meeting Abstract

  • U.-J. Hwang - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • H. Jung - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • J. Rah - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • S. H. Ahn - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • Y. Lim - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • D. Kim - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • M. Yoon - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • D. Shin - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • S. Lee - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea
  • S. Y. Park - Proton Therapy Center, National Cancer Center, Goyang-si, Korea, Republic of Korea

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog094

DOI: 10.3205/09ptcog094, URN: urn:nbn:de:0183-09ptcog0946

Veröffentlicht: 24. September 2009

© 2009 Hwang et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Background: Proton therapy was considered as next generation radiotherapy and has been widely expanded with its excellent target conformity due to rapid drop of dose after reaching maximum energy deposition to the tumor target, so called Bragg peak. It can be also one of the prominent methods for eye treatment whose target is small and surrounded by critical organs. To treat such a small target requires precise determination of the beam range. Plastic scintillator can be alternative dosimeter for this case due to numerous advantages of scintillator.

In this study, scintillating fiber Dosimetry system was developed for low energy proton therapy and was compared with conventional dosimeter.

Material and methods: The commercial models of fiber type scintillator were used in this investigation. Some emits light in the blue region and the others have scintillation peaks in the green region of the spectrum. Their core materials are based on polystyrene and claddings are composed of polymethyl-methacrylate. The core diameter of these all cylindrical fibers was 0.5 mm and have very thin claddings relative to the core.

The scintillating light generated from these small, water proof and water equivalent scintillating fibers are coupled with PMMA based optical fiber cable of 0.5 mm total diameter whose surface is jacketed with black polyethylene to prevent unwanted light noise from environment. The guided light from the scintillator was coupled to a bialkali photo-cathode array of a high sensitive photo-multiplier tube. The photo-multiplier output was gathered by commercial data acquisition system. Measured signal during low energy proton beam irradiation was compared with widely used ion chamber Dosimetry system; Markus type chamber for depth profile and pinpoint type chamber as well as diode dosimeter for lateral profile. Proton beam has Bragg peak at range 5 cm and appropriate spread out Bragg peak at the same range.

Results: In the depth dose measurement of Bragg peak, the output signal from scintillating fiber showed a good agreement with the results from ion chamber except for high dose region which was under-estimated. This phenomenon is known to quenching effect of scintillator. The relation between scintillating light output and absorbed dose can be given by the following equation.

Equation 1

where dL/dx is the light output energy emitted per unit length, dE/dx is specific energy loss for a charged particle, S is efficiency of scintillator, and kB is quenching parameter which was determined in this investigation to use scintillator as a proton dosimeter. After quenching effect being corrected, the spatial resolution of our scintillating fiber was measured and it was proved to be at least comparable or higher than the results of diode dosimeter (Figure 1 [Fig. 1]).

Conclusion: The study showed that plastic fiber Dosimetry system can be used to high precision quality assurance system for proton therapy. Quenching effect that limits the use of scintillator on particle therapeutic dosimeter can be considered and numerically corrected to determine the beam range and dose rate. Quenching parameter in this study was identified as 0.002 and showed good agreement with any literatures. Corrected percent depth dose was compared with the results of ion chamber and diode Dosimetry, and showed decent conformity with each other.

This work was supported by the National Cancer Center Grant (NCC-0910210).