Long term stability of the performance of a clinical linear accelerator and Z-score assessment for absorbed dose to water quantity

摘要

Assessment of the z-score was used to evaluate the long term stability of the performance of a clinical linear accelerator. The absorbed dose to water in high energy photon beam was determined at the linear accelerator owned by the clinical dosimetry laboratory in the radiotherapy department of the "Coltea" Clinical Hospital. The z-score was calculated for the absorbed dose measurements made at reference conditions according to IAEA-398 standard, in 2011 and in 2015 following repairs made to the linear accelerator. The measurements were conducted using water proof ionization chambers in a water equivalent phantom at the reference point for a 10 cm × 10 cm field size and at SSD = 1 m. For each ionization chamber the reference points, were determined according to radiation beam quality. The measurements were performed in a photon beam at reference points of 5 g cm-2 and 10 g cm-2. z-score assessment for absorbed dose to water quantity was evaluated according to ISO 13528:2005. The values obtained were found to be in the limits of statistical performance, z = [-2; 2], concluding that laboratory performance is satisfactory.