Author: James Chun Lam Chow, Harry E Ruda 👨🔬
Affiliation: University of Toronto, Princess Margaret Cancer Centre 🌍
Purpose: FLASH radiotherapy (FLASH-RT) with dose rate greater than 40 Gy/s, has demonstrated potential in reducing normal tissue toxicity while maintaining tumor control. However, accurate and reliable dosimetry under these extreme conditions is a critical challenge. This study aims to identify water-equivalent materials suitable for fabricating nanowire-based optically stimulated luminescent dosimeters (OSLDs) to address the precise dosimetry needs of FLASH-RT. Water equivalence is essential for accurate dose measurements, and the unique properties of nanowires offer significant advantages for this application.
Methods: Monte Carlo simulations were performed using the BEAMnrc code to evaluate the water-equivalence of various OSL materials. A modified Varian 21 EX linear accelerator, configured for FLASH irradiation with a 12-MeV electron beam, was modeled. The water equivalence of each OSL material was determined by calculating the ratio of the dose deposited in the OSLD to the dose in water at the same location. The dimensions of the OSLDs were set to 1×1×0.2 cm³. Materials studied included ZnBeO, Al₂O₃:C, KMgF₃:Ce, and others.
Results: The Monte Calro simulations indicated that most OSL materials exhibited dose ratios between 1 and 1.5, demonstrating reasonable water equivalence. Among the materials studied, ZnBeO showed the closest dose ratio to 1, making it the most water-equivalent material. Conversely, materials like KBr:Eu and Y₃Al₅O₁₂:C exhibited significantly higher ratios, exceeding 4. The superior water equivalence of ZnBeO, combined with its sensitivity and stability, positions it as a good candidate for nanowire-based OSLDs.
Conclusion: Nanowire-based OSLDs have exceptional sensitivity due to its large surface-to-volume ratio, rapid response time, and ability to provide precise dose measurements in FLASH-RT. While water equivalence is a critical factor in selecting materials, other considerations, such as ease of fabrication and durability are also important. This study identifies the water-equivalent material for OSLD fabrication, paving the way for advanced dosimetry solutions in FLASH-RT.