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Dosimetry using plane-parallel ionization chambers in a 75 MeV clinical proton beam
Hugo Palmans1, Frank Verhaegen, Jean-Marc Denis
1Subatomic and Radiation Physics Department, Ghent University, Belgium. Hugo.Palman@rug.ac.be
Physics in Medicine and Biology
|September 12, 2002
Summary
Plane-parallel ionization chambers are a reliable alternative for proton beam dosimetry, especially in challenging dose gradients. Experimental data and Monte Carlo simulations confirm their accuracy, supporting current dosimetry protocols.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Proton Therapy
Background:
- Reference dosimetry in clinical proton beams typically uses cylindrical ionization chambers.
- Plane-parallel chambers may be advantageous in regions with steep depth dose gradients or narrow spread-out Bragg peaks (SOBP).
- Limited research exists on the performance of plane-parallel chambers in proton beams.
Purpose of the Study:
- To experimentally evaluate perturbation correction factors for various plane-parallel ionization chambers in clinical proton beams.
- To compare the performance of plane-parallel chambers against a standard cylindrical chamber (NE2571).
- To validate findings using Monte Carlo simulations.
Main Methods:
- Experimental measurements of perturbation correction factors for four types of plane-parallel chambers (Roos, NACP02, Calcam-2, Markus) in 75 MeV proton beams.
- Monte Carlo simulations to support experimental results.
- Comparison of experimental and simulated correction factors relative to a cylindrical NE2571 chamber.
Main Results:
- Experimental perturbation correction factors for plane-parallel chambers showed minimal deviation from unity (≤1.2% relative to NE2571).
- Monte Carlo simulations corroborated these findings, with corrections generally within 0.6% absolute value.
- No significant differences were found between secondary electron perturbation correction factors for plane-parallel and cylindrical chambers.
Conclusions:
- Plane-parallel ionization chambers are a reliable alternative for reference dosimetry in low-energy proton beams.
- The assumption of a unity perturbation correction factor for plane-parallel chambers in proton beams, as used in dosimetry protocols like IAEA TRS-398, is experimentally supported.
- Plane-parallel chambers offer a viable alternative to cylindrical chambers, particularly where gradient corrections for cylindrical chambers introduce significant uncertainties.