Comparative dosimetric analysis of flattening-filter and flattening-filter-free photon beams in radiotherapy based on TRS-398 calibration protocol.

BACKGROUND: In external beam radiotherapy, delivering an accurate radiation dose is essential to ensure treatment effectiveness while minimising harm to surrounding healthy tissue. In Indonesia, the adoption of flattening-filter-free (FFF) technology remains limited, making its evaluation highly relevant for supporting more equitable radiotherapy services nationwide. The FFF technique offers advantages such as higher dose rates, shorter treatment time, and reduced head scatter, providing opportunities for faster and more precise treatment. This study compares the output dose deviations between flattening-filter (FF) and FFF modes using the IAEA TRS-398 dosimetry protocol. MATERIALS AND METHODS: Measurements were performed using a Varian TrueBeam linear accelerator with 6 MV and 10 MV FF beams and a 6 MV FFF beam. Absolute dose calibration was conducted with a calibrated ionisation chamber and electrometer in a water phantom at a reference depth of 10 cm. Data were collected from April to August 2025, with five repeated measurements for each energy. RESULTS: The results showed dose deviations of 0.908% (6 MV), 0.876% (10 MV), and 0.020% (6 FFF), which are all within the ±2% allowed by TRS-398. Among the evaluated modes, the FFF beam demonstrated the highest output stability. CONCLUSIONS: Both FF and FFF photon beams meet the TRS-398 standards for how accurate the radiation dose should be. But, the FFF mode is more stable, so it could be used more in hospitals, especially for very precise radiotherapy. These results show that FFF technology can make radiotherapy better, especially in places where the newest equipment is not available.