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Performance of a multi-axis ionization chamber array in a 1.5 T magnetic field
K Smit1, J G M Kok, J J W Lagendijk
1Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX, Utrecht, The Netherlands.
Physics in Medicine and Biology
|March 15, 2014
Summary
The IC PROFILER™ (ionization chamber array) performs reliably in a 1.5 T magnetic field, crucial for MR-linac quality assurance. Its measurements remain accurate and reproducible, unaffected by magnetic field exposure.
Area of Science:
- Medical Physics
- Radiation Oncology
- Magnetic Resonance Imaging
Background:
- The integration of magnetic resonance imaging (MRI) with linear accelerators (linacs) in MR-linac systems presents unique challenges for radiation dosimetry.
- Accurate quality assurance (QA) is essential for ensuring patient safety and treatment efficacy in MR-guided radiotherapy.
- The IC PROFILER™, a multi-axis ionization chamber array, is a potential tool for QA in these complex environments.
Purpose of the Study:
- To evaluate the performance and reliability of the IC PROFILER™ ionization chamber array within the strong magnetic field of a 1.5 T MR-linac.
- To investigate the influence of the 1.5 T magnetic field on key dosimetric characteristics of the IC PROFILER™.
- To validate the IC PROFILER™'s measurements against established methods, such as film dosimetry, in an MR-linac setting.
Main Methods:
- The IC PROFILER™ was tested in a prototype MR-linac (8 MV Elekta linac, 1.5 T Philips MRI).
- Performance parameters assessed include reproducibility, dose response linearity, pulse rate frequency dependence, power to electronics, panel orientation, and ionization chamber shape.
- Dose profiles from the IC PROFILER™ were compared with simultaneously acquired film dose profiles.
Main Results:
- The IC PROFILER™ demonstrated unaffected linearity, reproducibility, pulse rate frequency dependence, panel orientation, and ionization chamber shape in the 1.5 T magnetic field.
- Measurements normalized to a centre reference chamber remained unaltered, indicating the system's robustness.
- Comparison with film dosimetry revealed deviations attributed to film noise, confirming the IC PROFILER™'s accurate performance in the transverse magnetic field.
Conclusions:
- The IC PROFILER™ is suitable for quality assurance measurements in a 1.5 T MR-linac environment.
- Care must be taken when orienting ionization chambers and normalizing results from different axes due to magnetic field effects.
- The IC PROFILER™ provides reliable dose profile data, validated by comparison with film dosimetry in the MR-linac transverse magnetic field.
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