Linear-accelerator X-ray output: a multicentre chamber-based intercomparison study in Australia and New Zealand

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• Accurate calibration of linear accelerator output is crucial for effective radiotherapy.
• Dosimetry intercomparisons ensure consistency and quality in radiation dose delivery.
• The Australasian region requires robust methods for verifying accelerator performance.

Purpose of the Study:

• To evaluate the accuracy of linear accelerator outputs across multiple radiotherapy centers.
• To assess the consistency of measured accelerator output against local calibration protocols.
• To identify potential variations in dosimetry practices within the Australasian region.

Main Methods:

• Conducted a Level III Dosimetry Intercomparison involving 47 linear accelerator beams at 36 centers.
• Measured accelerator output under reference conditions using a small-volume ionization chamber in water.
• Applied the International Atomic Energy Agency (IAEA) Technical Reports Series (TRS) 398 protocol for dose-to-water determination.

Main Results:

• The mean ratio of measured to locally-determined accelerator output was 1.003 ± 0.009 (1 SD), ranging from 0.981 to 1.024.
• No significant correlation was observed between the output ratio and the type of linear accelerator or the local output calibration protocol used.
• The small-volume ionization chamber demonstrated acceptable performance but showed minor sensitivity variations upon cross-calibration.

Conclusions:

• Linear accelerator outputs in the Australasian region are highly consistent with local calibration protocols.
• The IAEA TRS 398 protocol provides a reliable framework for dosimetry intercomparisons.
• Further investigation into ionization chamber cross-calibration stability may be warranted for enhanced accuracy.