Performance evaluation and quality control implementation of parallel plate ionization chambers using linear accelerator

Abstract

External beam radiotherapy uses an electron beams to treat superficial lesions. For the calibration of this type of beam, it is recommended to use parallel plate ionization chambers (PPIs). Therefore, a quality control program is necessary for this type of dosimeter. Thus, the objective of this work was to evaluate the performance and implement quality control of PPIs using linear accelerator (LA) electron beam. Four PPIs were evaluated: three PPC05 from Iba and one Roos Chamber from PTW. The tests performed were repeatability with two different methodologies, reading stability with voltage variation for four voltage configurations, response linearity and leakage. For the repeatability and stability of the reading with the voltage variation, the three PPC05 chambers presented large deviations when considering the first 5 readings. When disregarding them, the four chambers present deviations smaller than the tolerance. All chambers analyzed presented linearity correlation coefficients greater than 0.99, which demonstrates excellent linearity of response with the dose. The current leakage values ​​of the four cameras were less than 0.1%, showing excellent performance. Therefore, the work demonstrates that it is possible to use the LA electron beam to perform quality control tests on parallel plate chambers. Furthermore, it shows that when using the PPC05 chamber to calibrate the electron beam, it is recommended that, after applying voltage to the electrometer, a few readings are taken until they stabilize before considering them for calculating the dose.