Dose audit using a glass dosimeter for Radiation Therapy Facilities in East-Asian Countries

Abstract

A dose audit using a photoluminescent glass dosimeter was conducted in radiation therapy facilities in a number of East-Asian countries. The audit was performed for the reference condition of linac X-ray beams, which was a 10x10 cm2 field and a 10cm depth with a SSD of 90 cm. Eight facilities from 5 countries, China, Korea, Indonesia, Viet Nam and the Philippines, participated in this audit. The ratios of deviation between the user-stated dose and the NIRS measured dose were analyzed. Among 24 X-rays beams measured from 6 to 20MV, 22 beams were within optimum levels (±3%) and 1 beam was out of the optimum level but within the tolerance level (±5%). However, 1 beam exceeded the tolerance level. The standard deviation of the ratios of deviation was 1.4%. A thorough and lengthy investigation was performed regarding this beam, which was observed to have a large rate of deviation (+6.1%). Finally, the cause became clear when it was determined that an incorrect pressure value in the calibration of a monitoring unit had been used. This event shows the importance of external audit in radiation therapy.