Quality assurance of six cylindrical and two parallel plate chambers by radioactive check device: Influence of chamber age to its performance

Abstract

PurposeTo evaluate the performances of eight ionization chambers, (two types) manufactured in a time span of 14 years, with radioactive source devices and photon beams. MethodsThe measurements were performed with six Farmer and two parallel plate ionization chambers with appropriate radioactive check devices and accompanying inserts. Some tests were performed with photon beams at linear accelerator. Physical visibility check, stability, linearity of response, directional dependence, determination of leakage current, ion recombination and polarity effect and influence of background radiation tests were conducted and analyzed. ResultsThe performance of all Farmer ionization chambers was in agreement to IEC standard as well as for parallel plate type chambers. Long-term stability of older planparallel chamber was somewhat worse than expected. ConclusionRadioactive check devices have proven to be easy to use in clinical environment. According to results of this work Farmer type ionization chambers showed good quality regardless of the time of production, which make them long-term suitable for clinical dosimetry in radiotherapy. Also, for parallel plate type of ionization chambers the results showed fine agreement with the IEC standard, except long-term stability for older chamber, which needs further investigation.