Speaker
Description
Within the scope of radiotherapy quality control, external dosimetry audits are essential for identifying systematic errors, improving treatment quality and safety, and promoting standardized dosimetry practices. In this study, the performance of linear accelerators was evaluated using a novel alanine/EPR-based postal dosimetry audit system developed at the Nuclear Energy Department of the Federal University of Pernambuco (DEN/UFPE), Brazil. The system was designed to assess photon beams under reference and non-reference conditions, allowing the simultaneous irradiation of six dosimeter holders and the evaluation of central-axis, off-axis, and depth doses, as well as beam quality index, flatness, and symmetry. Its validity was confirmed through interlaboratory comparison with the postal audit system of the Brazilian National Cancer Institute. Once validated, the DEN/UFPE audit system was employed to evaluate the performance of twelve linear accelerators installed in eight Brazilian radiotherapy centers. For the audits, the setup was irradiated with 6 MV photon beams, delivering a dose of 10 Gy at a depth of 10 cm, with a dose rate of 600 MU/min, a 10 x 10 cm² radiation field, and a SSD of 100 cm. EPR measurements of the alanine pellets were performed using a Bruker Magnettech ESR 5000 spectrometer operating in X-band. The values obtained for each physical or dosimetry parameter were compared with those declared by each participating center through the evaluation of percentage deviations. All audited equipment exhibited performance consistent with the established acceptance criteria. Moreover, it was found that 100% of the linear accelerators remained within the ±3% percentage deviation range for parameters associated with central-axis doses and beam profile. Therefore, in addition to demonstrating the consistency of the dosimetry protocols adopted by the participating institutions, the results highlight the potential of the DEN/UFPE audit system to enhance dosimetry accuracy in radiotherapy centers and to strengthen medical physics practices.