Dosimetric verification of annual quality assurance for a linear accelerator using a transmission type detector.

The purpose of our study is to establish an efficient quality assurance (QA) procedure using a transmission-type detector (IBA, Stealth chamber), a reference signal detector, as a field chamber. Relative dosimetry items, including monitor unit linearity, output constancy based on dose rate and field size, and output factor were measured and compared with results obtained from the Farmer-type chamber (IBA, Wellhofer, FC65-G). Moreover, output for each field size was measured to assess its applicability to small fields. Results using the Stealth chamber were in good agreement with the FC65-G within 1.0%, except for output constancy according to gantry angle, which had a 1.1% error rate for the Stealth chamber and 2.7% for the FC65-G. Differences of up to - 6.26% output factor were observed for the Stealth chamber and up to - 0.56% for the CC-13 ionization chamber (IBA) in the 3 × 3 cm field. Our study confirmed the possibility of using Stealth chambers for relative dosimetry measurement in QA.