Author: Xun Jia, Heng Li, Wen Li, Devin Miles, Daniel Sforza, Lingshu Yin, Yuncheng Zhong 👨🔬
Affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Johns Hopkins University 🌍
Purpose: FLASH therapy holds great potential to revolutionize radiotherapy by minimizing toxicities of normal tissues. The extraordinarily high dose rate of FLASH proton beam makes precise delivery to the target critical to prevent damage to surrounding healthy tissues. To ensure accurate beam delivery, we employed a multi-detector PET system to image the FLASH beam and present our observations.
Methods: The experiments were conducted on a home-built PET system consisted of 12 dual readout detector panels, each with 30 × 30 array of 1 × 1 × 20 mm3 LYSO crystals. The FLASH proton beam with 142.4 MeV was delivered to a cylindrical solid water phantom with 28 mm in diameter and 70 mm in length. The phantom was initially placed at center of FOV, with a 10.6 cm-thick solid water slab positioned upstream of the PET system and phantom. After first irradiation, the couch was shifted laterally by 5 mm, and thickness of the solid water slab was reduced to 10 cm for the second irradiation. The acquisition time was 11 seconds continuously, resulting in 11 recorded list-mode datasets. The recorded coincidences were reconstructed into PET image with spatial resolution of 1×1×1 mm3 using MLEM algorithm, representing the distribution of positron-emitting isotopes.
Results: Our findings demonstrate that the multi-detector PET system effectively recorded the PET signal generated by FLASH beam in the phantom. The recorded coincidences aligned with expectations, showing a gradual decay over time, with a logarithmic decay constant of 0.18. Additionally, the system accurately located the phantom in 3D space, achieving precise lateral localization and a 0.57 mm difference in range direction after the position shift.
Conclusion: The multi-detector PET proved to be a promising tool for 3D imaging and dosimetry of the FLASH beam, which holds great potential for imaging and monitoring of irradiation in FLASH therapy.