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Proton beam output measurement with an extrapolation chamber
C Zankowski1, S Vatnitsky, J Siebers
1Department of Medical Physics, McGill University, Montréal, Quebéc.
Summary
An uncalibrated extrapolation chamber offers a practical method for measuring proton beam dose rates. This method showed a 5% discrepancy compared to calibrated chambers, but may simplify output measurements.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Accurate dose rate measurement is crucial for proton beam therapy.
- Current dosimetry methods can be complex and require calibration.
Purpose of the Study:
- To evaluate an uncalibrated extrapolation chamber for measuring dose rate in a clinical proton beam.
- To compare its performance against a calibrated Farmer-type thimble chamber.
Main Methods:
- A variable air-volume, parallel-plate extrapolation chamber integrated into a polystyrene phantom was used.
- The chamber's sensitive air volume was controlled by a micrometer-driven piston.
- Proton beam dose rate was measured at a specific depth in the phantom.
Main Results:
- The uncalibrated extrapolation chamber yielded dose rates 5% lower than the calibrated Farmer-type thimble chamber.
- The extrapolation chamber's air volume was precisely controlled using a micrometer and distance indicator.
Conclusions:
- Uncalibrated extrapolation chambers provide a simple and practical alternative for proton beam output measurements.
- Despite a minor discrepancy, this method shows promise for clinical applications.