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

The quality assurance (QA) of the output constancy of linear accelerators (linacs) is one of the most basic items for radiation therapy. The necessity and demand of the dosimetric audit is on the rise. We aimed at establishing an on-site dosimetric audit program with a plastic phantom in order to enrich the availability of dosimetric audit in Japan. By this, we developed and evaluated an on-site audit program in multiple institutions in 120 cases for photon and electron standard dosimetry and intensity modulated radiation therapy (IMRT) condition. For photon standard dosimetry, we evaluated the accuracies of institutional measured absorbed dose in 50 cases by this on-site audit program. For the electron standard dosimetry, we evaluated the accuracies of institutional measured absorbed dose in 25 cases. For IMRT condition, we evaluated the accuracies of the institutional calculated dose in radiation treatment planning systems in 45 cases. The agreements of the measured absorbed dose between our audit and the institutions were within±1.1% for photon standard dosimetry. The agreements of the measured absorbed dose between our audit and the institutions were within±2.1% for electron standard dosimetry. The agreements between the measured absorbed dose of our audit and the institutional calculated dose were within±2.1% for IMRT condition. We established an on-site dosimetric audit program with a plastic phantom and this program is suitable with tight criteria similar to criteria required for clinical QA.