External dose audits of high-energy radiotherapy photon beams in Japan

Purpose: Nine years have passed since the Association for Nuclear Technology in Medicine (ANTM) launched the external dose quality audit (EDQA) of high energy radiotherapy photon beams for radiotherapy departments in Japan. When EDQA was started, the object was limited to beams of reference condition (10cm square field size, 10cm depth in water) and was expanded to non-reference conditions of field size changes and wedge filter insertions in 2010. In this study we report the results of this EDQA and the present status of dose estimation in Japan evaluated from EDQA.Methods: In the EDQA by ANTM, radiophotoluminescent glass dosimeter (RGD) is used as the detector. ANTM send RGD elements and solid phantom to radiotherapy departments and RGD are returned to ANTM after the irradiation of a specified dose. The dose delivered to RGD is measured at Dose Calibration Center of ANTM and is compared to the dose stated by radiotherapy department. Results: Until March 2016, 3,351 beams of 784 therapy units from 629 departments have been audited. The numbers of beams are classified into 1,663 of reference condition, 1,103 of field size change and 585 wedge filter insertion. The averages of difference between measured and stated dose were 0.39% in reference condition, 0.19% in field changes and 0.17% in wedge filter insertions. The standard deviations were around 1% for all conditions. Conclusions: The external dose QA by ANTM shows that the status of dosimetry at radiotherapy departments in Japan is in satisfying level.International Congress of Medical Physics, 201