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

Performance of a flatpanel detector in scanned ion beams

Meeting Abstract

  • M. MartišŪkovŠ - German Cancer Research Center, Heidelberg
  • B. Hesse - German Cancer Research Center, Heidelberg
  • O. Nairz - Heidelberger Ionenstrahl-Therapiezentrum, Heidelberg
  • O. Jškel - German Cancer Research Center, Heidelberg

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. DŁsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog132

doi: 10.3205/09ptcog132, urn:nbn:de:0183-09ptcog1326

Published: September 24, 2009

© 2009 MartišŪkovŠ et al.
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Outline

Text

Background: Scanning ion beams are going to be increasingly used for dose delivery to the patients in the upcoming years. This dynamic beam delivery technique poses extensive demands on quality assurance (QA) of the treatment. At the same time, shortening of time required for QA procedures would allow to use the saved beam time for patient treatment. There is therefore an interest to replace radiographic films used for daily checks of beam parameters as well as arrays of ionization chambers used for patient dose verification by a more efficient detector. It should comprise good spatial resolution and online readout.

Flatpanel detectors, used for photon portal imaging used within the latest generation of medical linear accelerators, are an interesting candidate for this purpose.

Materials and methods: We used the detector RID 256L (Perkin Elmer, Wiesbaden, Germany), which consists of 256 x 256 arrays of amorphous silicon photodiodes and thin film transistors with 800 Ķm pitch (Partridge M, Hesse BM, MŁller L. NIM A. 2002;484:351.). While basic characteristics in high energy proton beams were investigated in [1], in this work we concentrated on the measurement of the signal for different energies of both proton and carbon ion beams. Irradiations by protons and carbon ions were performed at the Heidelberg Ion Beam Therapy center, Germany using both, static and scanning beams. All acquired data were corrected for dead pixels and dark current.

Results: Timeresolved beam profiles in two dimensions were obtained for both beam modalities at different energies. They show high signal to noise ratio. An excellent linearity of the signal with the number of delivered particles was found. The measured signal was shown to be independent on the beam intensity within 0.5% and dependent on the ion type.

The detector response measured in monoenergetic proton and carbon ion beams shows strong energy dependence. This reveals the potential of the detector for radiographic purposes. Measurements of imaging properties using both, regular and irregular beam absorption structures, were performed in proton beams.

The depthdose curve measured in proton beams does not show quenching of the signal in the region of high ionization density in the Bragg peak. Such behavior is favorable for dosimetric measurements.

Furthermore, radiation damage and afterglow effects were investigated.

Conclusion: The investigated flatpanel detector can be used for fast and convenient qualitative measurements of beam profiles. Its imaging properties make it a promising candidate for daily QA measurements of beam parameters and for radiographic measurements. The energy and ion type dependence of the signal encourage further investigation of dosimetric measurements for patient dose verification in two dimensions.


References

1.
MartiiskovŠ M, Hesse B, Jškel O. Test of an amorphous silicon detector in medical proton beams. In: Proceedings of International Workshop on Radiation Imaging Detectors; Prague; 2009.