Purpose: A biology-guided radiotherapy(BgRT) capable system - RefleXion® X1 equipped with kVCT and PET imaging - was installed at our institution. This study reports quality assurance (QA) measurement results of the first clinical machine following the TG-148.
Methods: The mechanical, dosimetry and imaging QA procedures were established for intervals of daily, monthly, and annual. The daily QA was done using Tomodose to verify the laser and kVCT alignment, beam output. More comprehensive parameters including the output, beam quality and profile consistency were measured monthly using Tomodose and ion-chamber. The kVCT image quality was tested monthly using a Catphan phantom, and dynamic plan deliveries were tested using film. The first annual QA was performed including mechanical centering, alignment, and divergence of the source, MLC and y-jaws. The beam quality and profiles were measured using 3D water phantom and diodes. The TG-51 absolute calibration was also performed.
Results: Daily MV beam output constancy result showed the machine was stable over a year operation with standard deviation(SD) of 1.1%. The mechanical accuracy of the laser, couch shift, kVCT imaging and MV beam center were all within 1mm. Monthly TG-51 calibration was performed, and the output was tuned twice to maintain the output SD below 0.6%. The monthly mechanical test concluded that the SD from laser center to the imaging center was 0.64mm. The resolution, contrast, uniformity, noise, linearity, HU constancy and slice thickness of the kVCT stayed stable compared to the commissioning image qualities. The dynamic delivery film test confirmed that the deviation from the kVCT imaging center to the MV beam center was within 1mm. All mechanical, dosimetry, and imaging tests in the annual QA passed the tolerance suggested by the TG-148.
Conclusion: This evaluation represents the first complete QA results of the clinical BgRT system serving as a future reference.
Funding Support, Disclosures, and Conflict of Interest: This research was supported by a research fund from RefleXion Medical Inc