T. Dai1,2, A. Sloop1, M. Rahman3, J. Sunnerberg1, M. Clark1, R. Young4, S. Adamczyk4, P. Voigts-Rhetz4, C. Patane4, M. Turk4, L. A. Jarvis5, B. W. Pogue1,6, D. J. Gladstone1,7, P. Bruza1, and R. Zhang1,8; 1Thayer School of Engineering, Dartmouth College, Hanover, NH, 2Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, 3Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, 4IntraOp Medical Corporation, Sunnyvale, CA, 5Geisel School of Medicine at Dartmouth & Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon, NH, 6University of Wisconsin-Madison, Madison, WI, 7Department of Medicine, Geisel School of Medicine, Dartmouth College, Hanover, NH, 8New York Medical College, Valhalla, NY
Purpose/Objective(s): FLASH radiotherapy based on ultra-high dose rate (UHDR) is actively being studied by the radiotherapy community. Dedicated UHDR electron devices are currently a mainstay for FLASH studies. This work is to present the dosimetry and treatment planning tools for the UHDR capable compact electron linac for preclinical research and FLASH-radiotherapy (RT) clinical trials. Materials/
Methods: Film based dosimetry methodology has been established for the commissioning of UHDR electron linac. Monte Carlo (MC) beam model for treatment planning was configured and validated with Geant4-based GAMOS MC toolkit. The geometry and electron source characteristics, such as energy spectrum and beamline parameters, were tuned to match the central-axis depth dose (PDD) and lateral profiles for the pristine beam measured during machine commissioning. Diode-detector (UHDR capable) based beam monitoring method was implemented. To facility fast and accurate PDD measurements, MC model of the diode detector was configured, and its electron energy response was investigated. Correction method for the diode reading to facilize UHDR PDD measurements was established for routine use during preclinical research. Results: Preclinical research acceptable treatment planning method was established. Good agreement between the MC beam model and commissioning data were demonstrated with maximal discrepancy < 3% for PDDs and profiles. 100% gamma pass rate was achieved for all PDDs and profiles with the criteria of 2mm/3%. With the criteria of 2mm/2%, maximum, minimum and mean gamma pass rates were (100.0%, 93.8%, 98.7%) for PDDs and (100.0%, 96.7%, 99.4%) for profiles, respectively. Both film and diode detector showed good agreements in PDD measurements for UHDR electron beam. Conclusion: A validated MC beam model for the treatment planning of UHDR capable compact linac is presented for the first time. The beam model presented in this work should facilitate translational and clinical FLASH-RT for trials conducted on the compact UHDR electron platform.
