Author: Harsh Arya, Yan Chang, Yujie Chi, Varghese Anto Chirayath, Joshua Rajan, Pan Zui 👨🔬
Affiliation: University of Texas at Arlington, Department of Physics, University of Texas at Arlington 🌍
Purpose: In targeted alpha therapy (TAT), absorbed dose rates can vary significantly spatially and temporally, impacting therapeutic efficacy as well as carcinogenic potential. This study reports the development and validation of an alpha irradiation system for investigating dose rate effect in TAT.
Methods: The radiation system features a single Am-241 source mounted on a linear manipulator, a vacuum-based delivery system, a Si3N4 exit window to transfer the beam from vacuum to ambient conditions, and a programmable gate valve between the source and the exit window. The manipulator precisely controls the source-to-sample distance (SSD), therefore modulating the absorbed dose rate at the sample. The gate valve provides radiation protection to the exit window during non-experimental periods, ensures safety in the event of window breakage, and regulates radiation delivery during experiments. The system’s performance in aspects of beam energy and fluency at the sample position was measured by CR-39 detector and verified via SRIM.
Results: With a source activity of 4.81 MBq over an active area of 100 mm² and a vacuum condition of 4.0E-3 hPa, the system can achieve a dose rate of 1.5 to 3.4E3 by shortening the SSD from 500 mm to 10 mm. The performance was validated with SSDs of 330 mm and 432 mm in vacuum, followed by a 100 nm Si₃N₄ window. The alpha energy was measured as 4.556 ± 0.05 MeV with 210 and 121 alpha counts during a 15-second irradiation of a mm2 area. These measurements closely matched the simulation results of MeV with 212 and 122 counts. The Si3N4 window has a mean operating life of hours. The programmable gate valve can response to radiation delivery instruction or membrane rupture within 100-300 ms.
Conclusion: We successfully developed and validated an alpha irradiation platform capable of versatile dose rate control.