Performance parameters of a liquid filled ionization chamber array.

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate dosimetry is critical for effective radiation therapy.
• Liquid-filled ionization chamber arrays offer advanced capabilities for dose verification.
• The Octavius 1000SRS is a two-dimensional array designed for clinical photon-beam dosimetry.

Purpose of the Study:

• To investigate the properties of the Octavius 1000SRS array for clinical photon-beam dosimetry.
• To evaluate its performance in terms of stability, linearity, and spatial resolution.
• To assess its applicability in modern radiotherapy techniques.

Main Methods:

• Measurements were performed on Elekta Synergy and Siemens Primus accelerators.
• Stability, linearity, and saturation effects were assessed using a Semiflex 31013 ionization chamber as reference.
• Effective point of measurement, response with varying field size/depth, and output factors were determined using reference chambers and diodes.
• Dose response functions, low-pass properties, and sampling frequencies were theoretically evaluated.
• IMRT field verification was conducted using the Gamma-Index method.

Main Results:

• The array exhibited short-term ( < 0.1%) and long-term ( < 0.2%) stability.
• Linearity fluctuations were within ±0.2% for the specified dose range.
• Detector response showed minor energy dependence (±2.6% deviation).
• Gaussian dose response function σ-values were approximately 0.73 mm, with low-pass cutoff frequencies around 0.21-0.22 mm⁻¹.
• An IMRT field verification achieved a 95.2% passing rate with a 3 mm/3% Gamma-Index criterion.

Conclusions:

• The Octavius 1000SRS array is applicable for modern dosimetry, particularly in small field and stereotactic dosimetry.
• Output factor and dose profile measurements confirm its utility.
• The array's high spatial resolution ensures accurate dose profile measurements in various photon-beam fields, including IMRT.