S. Melemenidis1, M. R. M. Ashraf1, D. Chen2, K. Liu3, B. D. Velasquez3, L. Connell3, J. B. Schulz1, S. Dutt1, N. Katila1, K. Z. Flores1, E. Schueler3, and B. W. Loo Jr4; 1Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, 2Departments of Radiology and Radiation Oncology, Stanford School of Medicine, Stanford, CA, 3Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 4Department of Radiation Oncology, Stanford University, Stanford, CA
Purpose/Objective(s): Commercial devices capable of delivering FLASH radiotherapy are being introduced into radiobiology research. There is a critical necessity for a unified dosimetric protocol to ensure dosimetric consistency across institutes. This work introduces a collaborative, multi-institutional dosimetry protocol designed to validate and standardize dosimetry across two research facilities using FLASH intraoperative systems. Materials/
Methods: Two independent institutes used the same collimator design (4x4 cm2) and same beam parameters to deliver 12 or 14 Gy with FLASH or conventional (CONV) dose rates. For dosimetry, replicates of a realistic anatomy 3D-printed mouse phantom with coronal or sagittal division allowing insertions of radiochromic films, and a set of films (sourced from a singular source) were sent from Institute 1 to Institute 2. The institutes independently calibrated the target doses for FLASH using films from the phantom against the associated measurements from the embedded toroid of the system, and for CONV against the total number of MU. Ultimately, 80 experimental toroid measurements for FLASH (40 per target dose) were acquired in 4 days, with 5 set of films per modality per day of measurement. The films were returned to Institute 1 for analysis and the experimental values for FLASH and CONV were calculated. Results: For 12 Gy target dose, the toroid-derived FLASH doses combined for Institute 1 vs Institute 2 were 11.85 ± 0.11 Gy vs 12.32 ± 0.16 Gy, for 14 Gy were 14.12 ± 0.07 Gy vs 14.09 ± 0.01 Gy. for CONV 11.74 ± 0.23 Gy vs 12.19 ± 0.20 Gy and for 14 Gy were 13.86 ± 0.21 Gy vs 14.47 ± 0.31 Gy. Conclusion: The differences between measured and target doses, as well as between FLASH and CONV doses, were within 3%, and the inter-institutional dose differences were under 5%. Enhancing the protocol could entail incorporating an extra calibration step before the experimental dates to fine tune dose alignment between institutions. The success of the collaborative, multi-institutional dosimetry protocol, using realistic anatomy 3D-printed mouse phantom, is evidenced by the demonstrated consistency in preclinical radiobiological experiments across distinct research facilities.
