The characteristics of small field beam quality and output factor of 6 MV FFF

Flattening filter free linear accelerator (FFF LINAC) has been installed in Indonesia. To ensure the accuracy of FFF irradiation, we evaluate the characteristic of FFF in regular and small fields. We employed the Monte Carlo (MC) simulation of FFF LINAC 6 MV as a standard reference in this study. Then, we compared the calculation of FFF beam at central and lateral axis to the measurement and TPS at 10 × 10, 1 × 1, 2 × 2, 3 × 3, 4 × 4 cm² field sizes. Output factor (OF) and beam quality such that TPR_20,10 and penumbra of FFF LINAC were evaluated. TPR_20,10(S) for 10 × 10 cm² was 0.01 differ between MC and measurement whereas it varied from 0.588 to 0.703 for small fields. Dose difference of lateral axis was agreed within 3% except for the penumbra region. Output factor of small fields measurement indicated that field size of 1 × 1 cm² had a large discrepancy to MC according to this works. The TPR_20,10(10) of MC, TPS, and measurement was not a significant difference, while the OF was tending to a large deviation in 1 × 1 cm². The results showed that our FFF LINAC could be used for small field until 2 × 2 cm². (paper)