Uniformity calibration for large area XY strip parallel plate ionization chamber

Area of Science:

• Medical Physics
• Radiation Detection and Measurement

Background:

• Large area ionization chambers (LAICs) offer advantages for monitoring therapeutic radiation beams.
• Ensuring uniform detector response is critical for accurate clinical dosimetry with LAICs.

Purpose of the Study:

• To develop and validate a systematic uniformity calibration method for large area parallel plate ionization chambers (PPICs).
• To improve the lateral response of PPICs for accurate dosimetry in radiation therapy quality assurance.

Main Methods:

• A large area XY strip PPIC (345.44 × 345.44 mm², 256 channels) was investigated.
• A 2D response map was generated using a mini x-ray tube and spot-scanning.
• The calibration utilized the 2D response map to correct for heterogeneous detector responses.

Main Results:

• Before calibration, the PPIC showed response deviations up to 7%, exceeding the 1% IAEA TRS-398 recommendation.
• The developed calibration significantly improved uniformity to less than 1% across the detector surface.
• The method demonstrated effectiveness for both narrow and large field beams.

Conclusions:

• The proposed uniformity calibration method enables reliable application of PPICs in routine clinical dosimetry.
• These methods can be adopted by radiation facilities for daily and monthly quality assurance.
• Improved detector uniformity enhances the accuracy and reliability of radiation therapy monitoring.