Purpose: Reflexion X1, the first biology-guided radiotherapy (BgRT) system equipped with PET imaging, was installed at our institution. This study reports the QA and commissioning results of the X1 system following the TG-148 protocol.
Methods: The X1 linac produces 6MV flattening filter free beams with a dose rate of 850cGy/min. The rotational treatment fields are modulated by a binary multi-leaf collimator (MLC) with 64 leaves with 6.25mm leaf width at 85cm SAD and IEC y-jaws switching between 1cm and 2cm. The mechanical tests were performed to verify the centering, alignment, and divergence of the MLC and y-jaws. The beam parameters were commissioned using a 3D water phantom and a diode detector. Beam quality, transverse and longitudinal profiles of each slice width were measured and compared with the beam model. The localization accuracies of the laser and kVCT to MV beam isocenter were checked using a ball cube phantom.
Results: The source sweep test showed the y-jaw misalignment was 0.049mm. The y-jaw divergence was 0.36mm and the twist was 0.03°. The longitudinal field center variation along the x-axis was less than 0.03mm. The normalized MLC tongue-and-groove film result showed the x-axis out-of-focus value was 0.66%. The MLC alignment test showed an offset of 0.57mm and a twist of 0.15°. Comparing the measurement and TPS modeling, the PDD10 differences were 0.2% and -0.3%, and the mean transverse profile differences were 0.55% and 0.73% for the 40x2cm² and 40x1cm² fields, respectively. The FWHM differences of the longitudinal profiles were within 0.5mm. The localization accuracies of the laser and kVCT to MV isocenters were within 1mm.
Conclusion: This evaluation represents the first QA and commissioning evaluation of the clinical BgRT system as a future reference.
Commissioning, Quality Assurance
TH- External Beam- Photons: Quality Assurance - Linear accelerator