Correction for the angular dependence of a detector in electron and photon beams

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Radiotherapy Physics

Background:

• Accurate measurement of radiation dose is crucial in radiotherapy.
• Detector response can vary with the angular distribution of radiation.
• Understanding these variations is essential for precise dose delivery.

Purpose of the Study:

• To develop a simple analytic function to describe experimental angular response functions.
• To derive formulas predicting detector response variations with phantom depth.
• To analyze response changes in electron and photon beams for flat liquid ionization chambers.

Main Methods:

• Experimental acquisition of angular response functions.
• Fitting a simple analytic function to the experimental data.
• Derivation of formulas based on the analytic function to predict response variations.

Main Results:

• A simple analytic function was found to accurately fit experimental angular response data.
• Derived formulas predict detector response variations due to changing electron angular distributions with depth.
• For flat liquid ionization chambers, response variation is 2-4% in the build-up region for electron and photon beams.
• Detector response remains nearly constant beyond the dose maximum.

Conclusions:

• The developed analytic function provides an accurate method for characterizing detector angular response.
• The derived formulas enable prediction of detector response variations in phantom depths for clinical beams.
• Flat liquid ionization chambers exhibit minimal response variation beyond the dose maximum, simplifying dosimetry in these regions.