Dosimetric evaluation of linear accelerator SHINVA

Linac output is one of physical parameters which determine the dose delivery to patients. The constancy of Linac output is important to be evaluated. The study employed 6 MV Linac SHINVA XHA 600C for the measurements of the absorbed dose to water were carried out with 0.6 cc ionization chamber type NE 2571 Farmer. In addition, the Percentage Depth Dose (PDD) and dose profiles were measured in water phantom which was equipped with ionization chamber Exradin A28. The PDD and dose profile were evaluated in the radiation fields 8 × 8 cm2, 10 × 10 cm2, and 15 × 15 cm2. The study of performance of Linac machine was done from 2020 to 2022. The absolute dose deviations were 0.708 ± 0.259%, 1.581 ± 0.739%, and 1.584 ± 0.736% for 2020, 2021 and 2022 respectively. In general, the average of Linac output within the tolerance level, though the standard deviation increasing for 2021 and 2022. Furthermore, comparison the PDD to baseline data shows the highest average deviations are 0.467% in the field of 10 × 10 cm2 in 2020, 0.55% in 2021, and 0.492% in 2022. On the other hand, the flatness and symmetry has the highest deviation to baseline data at about 0.202% to flatness and 0.115% to symmetry for three years study. The average machine output performance of Linac Shinva are within 2% tolerance limit based on recommendation of AAPM TG 40 and 142 for daily and monthly dosimetry constancy. The performance of the PDD constancy, flatness, and symmetry are also within tolerances limit ± 2% compared to baseline commissioning data.