Preliminary Treatment Planning System Commissioning Results for the First Clinical Biology-Guided Radiotherapy Machine
N Kovalchuk1*, B Han1, E Simiele1, D Capaldi1, D Breitkreutz1, T Yeung2, J White2, D Zaks2, M Owens2, S Maganti2, A Purwar2, L Vitzthum1, D Chang1, L Xing1, M Surucu1, (1) Stanford Radiation Oncology, Stanford, CA (2) Reflexion Medical, Inc
Presentations
PO-GePV-T-329 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: To report the preliminary treatment planning system (TPS) commissioning results for the first clinical installation of Reflexion X1- biology-guided radiotherapy (BgRT) system. RefleXion TPS generates IMRT/SBRT plans using the gradient-descent-optimization and Collapsed-Cone-Convolution algorithm (2.1mm grid) for 6MV-FFF beam delivered axially via 50 firing positions with couch advancing every 2.1mm.
Methods: CT images of multiple phantoms were acquired and transferred to RefleXion TPS to test the accuracy of data acquisition, anatomical modeling, plan evaluation and dose calculation. Dosimetric parameters for various open static fields and SADs were evaluated in water and heterogeneous slabs phantoms. TG-119 and representative clinical IMRT/SBRT cases were planned and verified with ion chamber, film and ArcCheck (gamma:3%/2mm). End-to-end (E2E) testing was performed using anthropomorphic head and lung phantoms.
Results: The maximum difference between RefleXion TPS and known CT numbers was 10.3±6.0HU, maximum difference in the structure volume was 20.2±4.8cc(Eclipse) and 2.93±0.6cc(MIM); maximum difference in the structure dose was 5.0±1.2Gy(Eclipse) and 1.7±0.4Gy(MIM). For static fields, PDD10 matched between TPS and measurement within 0.8%, crossline profiles matched within 1.6% in 80% from CAX for all fields≥2.5cm, and inline profiles agreed within 0.5mm FWHM. Output factors matched scintillator measurements within 1% for all fields. Dose in heterogeneous slab phantoms agreed within 3.5%. Lung phantom verification with film passed with gamma≥98.6%. The ion chamber measurements for TG-119 plans were within 2.9%; and ArcCheck QA passed>90% for all plans. E2E film analysis showed 0.8mm total targeting error for isocentric and 1.1mm for off-axis treatments. Iterations to the beam model are in progress to further improve the passing rate for smaller targets<=3cm.
Conclusion: In this current preliminary report, the test results agreed within the tolerances specified by TG-53, MPPG 5.a, TG-119, TG244, and TG-148. A subset of the commissioning tests has been identified as a baseline data for an ongoing QA program.
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