[Establishment of an On-Site Dosimetric Audit Program with a Plastic Phantom]

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Quality assurance (QA) of linear accelerator (linac) output constancy is fundamental in radiation therapy.
• There is a growing need for accessible dosimetric audits to ensure treatment accuracy.
• Existing audit programs may have limitations in availability or scope.

Purpose of the Study:

• To establish and evaluate an on-site dosimetric audit program in Japan using a plastic phantom.
• To enhance the availability and accessibility of dosimetric audits for radiation therapy institutions.
• To assess the accuracy of institutional dosimetry for photon, electron, and intensity-modulated radiation therapy (IMRT) conditions.

Main Methods:

• Development and implementation of an on-site audit program utilizing a plastic phantom.
• Evaluation of 120 cases across multiple institutions, covering photon and electron standard dosimetry and IMRT.
• Comparison of institutional measured absorbed dose and calculated dose (for IMRT) with audit results.

Main Results:

• Photon standard dosimetry: Agreement within ±1.1% between audit and institutional measurements.
• Electron standard dosimetry: Agreement within ±2.1% between audit and institutional measurements.
• IMRT condition: Agreement within ±2.1% between audit measurements and institutional calculated doses.

Conclusions:

• An effective on-site dosimetric audit program using a plastic phantom has been successfully established.
• The program demonstrates suitability for clinical QA, meeting stringent accuracy criteria.
• This initiative improves dosimetric audit availability in Japan for critical radiation therapy QA.