295 - Development of a Robust FLASH Research Platform for In Vivo Spinal Cord Study with Image-Guided Dosimetry
Presenter(s)
B. Zhou1, L. Guo1, Y. C. Tsai1, J. W. Wong2, I. Iordachita3, R. Zhang4, V. A. Chirayath5, W. Lu6, K. Jiang7, P. M. Medin8, and K. K. H. Wang1; 1Biomedical Imaging and Radiation Technology Laboratory (BIRTLab), Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX, 2Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Baltimore, MD, 3Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, 4Department of Radiation Oncology, University of Missouri, Columbia, MO, 5Department of Physics, UT Arlington, Arlington, TX, 6Medical Artificial Intelligence and Automation (MAIA) Lab, Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX, 7Department of Radiation Oncology, UT Southwestern Medical Center, Dallas, TX, 8Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX
Purpose/Objective(s):
FLASH radiotherapy (FLASH-RT) delivers curative dose to tumors at ultra-high dose rates (UHDR, >40 Gy/s) while mitigating normal tissue toxicity. While most supporting evidence focuses on acute toxicity, data on late-responding organs remain limited. Establishing the dose-response relationship for late-responding organs is critical for the clinical translation of FLASH-RT. Due to the spinal cord's clinical significance and its steep dose-response curve, it serves as an ideal model to investigate whether FLASH can reduce late toxicity. Precise dosimetry is critical for rigorous FLASH spinal cord studies due to the rapid irradiation and the steep dose response curve. In this work, we introduce a robust FLASH research platform for in vivo spinal cord study with image-guided dosimetry.Materials/Methods:
A modified linear accelerator (LINAC) was used to irradiate the cervical-thoracic spine (C1-T2) of rats with 18 MeV FLASH and conventional (CONV) electron beams, with a posterior-anterior 2×1cm2 field. To precisely monitor high dose per pulse (~2 Gy/pulse), we developed an external pulse control and monitoring system with single-pulse resolution. A high-precision Monte Carlo (MC) dose calculation system was also developed to ensure accurate dosimetry and support the interpretation of in vivo results. A custom rat immobilization device and an on-board X-ray imaging were designed for target localization. To further enable real-time dose and dose rate verification within the spinal cord against MC calculations, we integrated the X-ray imaging with a scintillator at 1000 Hz sampling frequency for radiation detection. Additionally, an ionization chamber (IC) was positioned beneath the electron cone to monitor Bremsstrahlung radiation as a surrogate for real-time UHDR output measurement.Results:
IC readings demonstrated excellent linearity with film measurements (R² = 0.999), which allows us using IC to monitor FLASH dose output during study. The integration of the immobilization device and image-guided system resulted in a highly reproducible setup, with positioning uncertainties < 2 mm. The MC calculations indicated that the 18 MeV FLASH beam achieved a profile non-uniformity of < 5% along the 12 mm length of the C1–T2, avoiding the spinal cord dose-volume effect that could confound FLASH sparing. FLASH dose measured by the scintillator closely matched with MC-calculated values, <4% difference within the central 12 mm C1-T2 region. The gamma passing rate across all measurement points was 100% (1 mm/3% criteria). These results confirmed the accuracy of the MC dose engine for spinal cord studies and demonstrated the feasibility of applying a scintillator for FLASH dosimetry.Conclusion:
A dedicated FLASH research platform was developed for spinal cord study, demonstrating accurate dose delivery, target localization, and dosimetry calculation and verification. This lays the groundwork to understand if FLASH-RT would spare late toxicities.