Author: Ahmet S. Ayan, Austin M. Faught, Eunsin Lee, Julia Pakela π¨βπ¬
Affiliation: Department of Radiation Oncology, The Ohio State University Wexner Medical Center, Ohio State University, The Ohio State University π
Purpose: To present commissioning of a fixed beamline ultra-high dose rate proton pencil beam scanning system, the worldβs first multi-room Varian ProBeam360β°
Methods: The fixed beamline pencil beam scanning proton therapy system delivers FLASH plans with pre-defined spot lists using a 226 MeV transmission beam at dose rates exceeding 40 Gy/s. Beam data collection, commissioning, and characterization of the delivery system were performed using parallel plate ion chambers, radiochromic film, and other scintillator-based detectors. A treatment beam model was created and validated. A quality assurance program was adapted to include FLASH-specific irradiation. Using machine logfile, a voxel-based local dose rate calculation tool was developed to characterize dose rate as a function of nozzle currents, number of spots, and spot MUs for given machine limits.
Results: The measured R80 of 317.7 mm for the energy of 226 MeV differed by 0.5 mm from the nominal value. Spot size (Ο) was measured as 3.5 mm and 3.6 mm along x and y profiles, respectively. The agreement of the output measurement and prediction of TPS modeling was within 0.4%. For a given linear relation between MU per spot and nozzle current within the inherent machine limits, maximum dose rates of user-specific, pre-defined spot lists were calculated and validated using logfile analysis.
Conclusion: A FLASH-capable fixed beam line was successfully released for preclinical experiments. The beamline will contribute to pencil beam scanning-based proton beam FLASH research.