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Updated: Jun 24, 2026
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Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator
Published on: May 9, 2014
Development of a multi-layer ionization chamber for heavy-ion radiotherapy
Kaori Yajima1, Tatsuaki Kanai, Yohsuke Kusano
1Toho University Graduate School of Science, 2-2-1, Miyama, Funabashi, Chiba 274-8510, Japan. yajima@nirs.go.jp
Physics in Medicine and Biology
|March 19, 2009
Summary
A new multi-layer ionization chamber (MLIC) improves dose accuracy in proton therapy. This revised design enhances water equivalence, crucial for precise measurements in spread-out Bragg peaks (SOBP) for better patient treatment.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Particle Therapy
Background:
- The National Institute of Radiological Science (NIRS) developed a multi-layer ionization chamber (MLIC) for MU calibration in 2002.
- Existing MLICs require corrections for accurate dose assessment at the spread-out Bragg peak (SOBP) center in water phantoms due to insufficient water equivalence.
Purpose of the Study:
- To develop an improved multi-layer ionization chamber (MLIC) with enhanced water equivalence.
- To overcome the limitations of previous MLIC designs in accurately measuring depth dose distributions, particularly at the SOBP center.
Main Methods:
- A new MLIC was constructed using polymethyl-methacrylate (PMMA) plates and graphite electrodes, replacing FR4 and copper.
- Calibration coefficients were determined using a 160 MeV proton beam.
- The performance of the new MLIC was evaluated for carbon-ion beams.
Main Results:
- The newly developed PMMA-based MLIC demonstrates improved water equivalence.
- The PMMA MLIC can measure depth dose distributions in water phantoms with less than 2% error.
- Accurate measurements were achieved even in the fragment tail region of the dose distribution.
Conclusions:
- The revised MLIC design using PMMA and graphite significantly improves dose measurement accuracy in water phantoms.
- This enhanced MLIC is suitable for precise depth dose distribution measurements in particle therapy, including carbon-ion beams.
- The improved water equivalence addresses previous limitations, enabling more reliable dosimetry for clinical applications.
