Dosimetry audit for megavoltage photon beams applied in non-reference conditions

Area of Science:

• Medical Physics
• Radiotherapy Dosimetry
• Quality Assurance in Radiation Oncology

Background:

• Accurate dose delivery is critical in external beam radiotherapy.
• Non-reference conditions pose challenges for dosimetry accuracy.
• Systematic errors in the dosimetry chain can compromise patient safety.

Purpose of the Study:

• To conduct the first Malaysian postal dosimetry audit for external beam radiotherapy under non-reference conditions.
• To evaluate output performance and screen for systematic errors in the dosimetry chain.
• To investigate detector choices and identify sources of discrepancies.

Main Methods:

• Audited ten radiotherapy centers, covering 16 megavoltage photon beam arrangements.
• Utilized the IAEA postal dosimetry protocol for non-reference conditions.
• Employed three types of thermoluminescent dosimeters (TLDs): Ge-doped cylindrical silica fibres (CF), Ge-doped flat silica fibres (FF), and TLD-100 powder.

Main Results:

• Eight centers met the ±5% dose tolerance; one exceeded it, and one failed initial irradiations.
• Post-remedial measures, mean relative responses for CF, FF, and TLD-100 were 1.00, 0.99, and 0.98.
• Coefficients of variation for CF, FF, and TLD-100 were 6.87%, 6.45%, and 5.06% respectively.

Conclusions:

• High-quality postal dosimetry audits using sensitive TLDs are effective in identifying dose discrepancies.
• These audits aid in resolving dose delivery issues in clinical radiotherapy practice.
• The study highlights the importance of regular audits for maintaining radiotherapy quality.