The Annual Quality Assurance of Linear Accelerator using a Stealth Chamber: A Comparison between a Transmission-type and Farmer-type Chamber

Abstract The purpose of our study is to establish an efficient quality assurance (QA) procedure using a Stealth Chamber—a reference signal detector—as a field chamber. Among the annual QA items, relative dosimetry items such as monitor unit linearity, output constancy according to dose rate, and output constancy according to gantry angle, and the output factor according to the field size were measured and compared with the results of the Farmer-type chamber for True Beam and Halcyon. In addition, output measurement was performed for each field size to evaluate the applicability to small fields. The results obtained using the Stealth Chamber for all items, except for the output constancy according to the gantry angle, were in good agreement with that obtained using the Farmer-type chamber within 1.0%. In the measurement of output constancy items according to gantry angle, the stealth chamber had an error of up to 1.1%, while the Farmer-type chamber had an error of up to 2.7%. The Stealth Chamber had a difference of up to 6% output factor, and in the case of CC13 Ionization Chamber, there was a difference of up to 13% output factor in a small field of 1 x 1 cm2. Our study confirmed the possibility of performing relative dosimetry measurement items among QA items using stealth chambers, especially useful for small field dosimetry of equipment without light fields such as halcyon.