Development of a Mailable Pre-Clinical Flash Phantom for Remote Auditing of Ultra-High Dose Rate (FLASH) Radiotherapy
Abstract
Purpose
To design and validate a phantom capable of remote temporal and point dose rate assessment for electron and proton FLASH beams, with integrated spatial information to enable full end to end verification.
Methods
A PMMA phantom was machined to three key components: (1) an embedded high-speed diode synchronized with a microcontroller capable of sampling rates greater than 1MHz acquisition for pulse waveform capture, (2) Gafchromic film for spatial dose mapping, and (3) thermoluminescent dosimeters (TLD) for integral dose verification. Electron deliveries of 4, 8, and 20 Gy at 1 and 4 Gy/pulse, and proton deliveries using single spill operation were tested. Diode signals were timestamped and synchronized to machine triggers. Temporal metrics (pulse width, repetition rate) were compared against a Beam Current Transformer (BCT) for electrons and a calibrated A10 monitor chamber for protons.
Results
Temporal outputs for both modalities agreed within 1.0% of the BCT (electrons) and A10 (protons). Point dose rate reconstructions derived from diode waveforms matched reference systems within 1% across tested beams and dose levels, demonstrating high temporal fidelity and robust reconstruction under FLASH conditions. Physical dose assessment and spatial dose distributions were appropriately captured with TLD and film.
Conclusion
The phantom enables robust remote verification of temporal structure and dose rate reconstruction for FLASH beams, supporting standardized multicenter evaluation. This platform will be further developed and integrated into NCI FLASH trials through the Imaging and Radiation Oncology Core.