The Development of a Preclinical Alpha Irradiation Platform with Versatile Control of Dose, Dose Rate, and Spatiotemporal Irradiation Patterns

TL;DR

This work addresses the need for precise, multi-parameter control of alpha irradiation in preclinical radiobiology by developing a vacuum-based platform with independent tuning of incident energy, fluence rate, and spatiotemporal patterns. The authors validate the system using Geant4 and SRIM simulations alongside CR-39 detectors, demonstrating accurate temporal gating (±<0.3 s), MC-consistent fluence rates (within ~3%), controllable energy via thin degraders, and reproducible spatial patterns that follow programmed trajectories. Key contributions include a practical vacuum design with adjustable source-to-aperture distance ($d$), a gate-valve–driven temporal mechanism, energy-degradation layers, and a 3D stage for precise patterning, all achieving energy-degradation free delivery and versatile exposure schemes. The platform overcomes limitations of gas-filled systems and enables systematic studies of how energy, dose rate, and spatiotemporal patterns influence radiobiological responses, with implications for optimizing targeted alpha therapies and refining radiation protection frameworks.

Abstract

Objectives. This study develops and validates a vacuum-based alpha irradiation platform to support preclinical radiobiology. We aim to demonstrate precise, independent control over incident energy, fluence rate, and spatiotemporal patterns, which are critical to the mechanisms underlying targeted alpha therapies and low-dose risk assessments. Approach. A vacuum-based system with a radioactive alpha source was designed and fabricated. The platform provides independent modulation of: (i) temporal patterns via a programmable gate valve; (ii) fluence rate across two orders of magnitude by varying source-to-aperture distance (57 to 381 mm); (iii) incident energy (0 to 4.6 MeV) using adjustable absorption layers; and (iv) spatial distributions via a 3D motion stage. Temporal precision was assessed via synchronized audio-electronic recordings. Fluence rates and energies were validated using CR-39 detectors and Monte Carlo (MC) simulations. Spatial precision was verified through programmed continuous and discrete trajectories. Main results. Validation experiments demonstrated high system fidelity. Measured irradiation durations deviated from programmed values by less than 0.3 s. Measured and computed fluence rates agreed within 3%. For energy validation, CR-39 track diameters matched MC model predictions within one standard deviation. Recorded spatial patterns and dimensions aligned well with programmed trajectories. Significance. We successfully validated a versatile vacuum-based platform that overcomes energy-degradation constraints of gas-filled systems. By providing multi-parametric control over alpha-particle delivery, this system enables systematic investigation into how energy, dose rate, and spatiotemporal patterns influence radiobiological responses. This platform is poised to optimize targeted alpha therapies and refine radiation protection frameworks.

Figures (8)

• Figure 1: The overall design principle of the alpha irradiation platform. The system features vacuum-based fluence rate control, programmable gate valve for temporal radiation modulation, exit window--air gap--cell dish bottom stack for energy control, and a programmable 3D motion stage for precise spatial radiation delivery.
• Figure 2: Schematic illustration and physical implementation of the alpha delivery system. (a) 3D design model showing major components. (b) Photograph of the fabricated system.
• Figure 3: (a) Am-241 source placed inside a plexiglass box, with a ruler shown for scale.(b) Source mounting system installed inside the vacuum chamber.(c) Geant4-simulated alpha energy spectra before ("bare") and after ("Au-coated") transmission through a 2.0 $\mu$m gold layer.(d) Alpha energy spectra after transmission through a 330 mm vacuum path at pressures of $10^{-1}$, $10^{-2}$, and $10^{-3}$ hPa. Here, E1, E2, and E3 correspond to the three primary alpha emission energies of the Am-241 source: 5.388 MeV, 5.443 MeV, and 5.486 MeV, respectively.
• Figure 4: Principle of alpha-particle energy determination from CR-39 track measurements. (a) Geometry of etch pit formation for alpha particles with different energies corresponding to ranges $R_1$ and $R_2$. (b) Relationship between the track-to-bulk etch rate ratio ($V_T/V_B$) and the alpha-particle range in CR-39, as provided by Track Analysis Systems Ltd., UK (https://www.tasl.co.uk/downloads/tastrak-alpha-specifications.pdf).
• Figure 5: Time stamps for the programmed irradiation via gate valve control.