Introduction Toxicity and efficacy mechanisms remain largely unknown for targeted alpha therapy (TAT) with Ac-225. This is driven by two aspects of TAT treatments with Ac-225: the heterogeneous distribution of radiolabeled vectors within tumors and normal organs and the complex Ac-225 decay chain: daughter alpha emitters which can redistribute independently of the parent vector, leading to activity uptake in some specific organs. Both aspects make accurate dosimetry challenging. In this context, we present a new autoradiographic method that combines a position sensitive charge-particle detector and a gamma spectrometer, to spatially tag selected daughters in the Ac-225 decay chain. By separating the spatial distributions of these daughters, we can generate micrometric (∼20 μm) isotope-specific activity maps, which will in turn support estimating their individual local dose-rate contributions. Objectives We aimed to develop a spectroscopic autoradiographic method to differential Ac-225 decay-chain elements for improving dosimetry calculation at the microscopic scale. Materials and Methods The present study is based on an autoradiographic system combining a gamma spectrometer and a large–field-of-view gaseous charged-particle detector, enabling isotope discrimination and spatial localization with high spatial resolution (∼20 μm) through (α,β)/γ time-coincidence (TC). This setup aims to capture only the photon signal at the instant a β particle triggers the autoradiograph electronics. Two samples were analyzed with the TC algorithm: (i) a drop of Ac-225 solution at secular equilibrium was used to characterize the time-coincident γ spectrum and (ii) an Ac-225-DOTATOC solution eluted on an instant thin-layer chromatography (iTLC) plate to assess the spatial identification of daughter nuclides. To fully understand the Ac-225 coincidence spectrum equilibrium dependence, the setup was modeled with the Geant4 Monte Carlo (MC) simulation. Results The TC γ-spectrum of Ac-225 sample at secular equilibrium, corroborated by the MC simulation, shows well-defined (8.8% FWHM @ 440 keV), high-intensity photopeaks that allowed Fr-221 and Bi-213 tagging by energy gating. This method was applied to the iTLC sample with differential migration, where Ac-225-DOTATOC remained at the deposition origin, while unchelated daughter nuclides migrated along the plate. Hence, we generated isotope-specific 2D maps of daughter to Ac-225 activity ratios. Conclusion This work demonstrated the feasibility of spatially resolved isotope tagging on non-biological Ac-225 samples, using (α,β)/γ TC. Extended to autoradiographic imaging of tissue, this approach will enable sub-millimeter maps of daughter-specific activity distributions, allowing for more accurate local dose-rate estimation in preclinical targeted alpha therapy studies. This capability supports both efficacy (on-target dose) and toxicity (off-target dose) assessment by quantifying microscale dose heterogeneity from daughter redistribution. Beyond Ac-225, the same framework could be applied to other alpha-emitters such as At-211, Ra-223 or Th-227, providing a general tool for TAT research under equilibrium and redistribution conditions. Funding Acknowledgements This work was supported by the LabCom AIDA (ANR-23-LCV1-0003-01)), funded by the French National Research Agency (ANR) and the “Région Pays de la Loire” (Project TN_2024_LABCOM_AIDA_Lab_GLISSANDO). We would also like to thank the AlphaMet consortium.

Introduction Targeted Alpha Therapy (TAT) with Ac-225 requires rigorous quality control (QC) to ensure radiochemical purity (RCP) prior to preclinical or clinical use. Current QC protocols rely on thin-layer chromatography (TLC) imaged after secular equilibrium (> 12 h), delaying batch release and limiting experimental throughput. We developed a rapid and predictive QC approach using digital autoradiography combined with temporal fitting, enabling reliable RCP assessment within one hour. Objectives To establish a robust, non-destructive, and time-efficient QC method for Ac-225-labeled radiopharmaceuticals, allowing RCP assessment within one hour without waiting for equilibrium. Materials and Methods Ac-225 was chelated to DOTA-TOC under standard radiolabeling conditions. One μL of labeled solution were spotted 1 cm from the bottom of iTLC-SG strips and developed (8–10 min to 8 cm) in citrate buffer (0.1 M, pH 5) as eluent. DTPA was used as a free-chelator reference to identify the migration front of unbound Ac-225. Drying was optimized (approximately 15 min) using a blade-type dryer (BLINDED). Identical TLCs were analyzed on a digital autoradiography system (BLINDED) and on a phosphor-imaging system (BLINDED). Autoradiography began 15 min post-migration and continued for up to 100 min, while phosphor imaging was performed after 24 h to reach secular equilibrium. Temporal fitting based on Bateman modeling uniquely enabled rapid isotope-specific quantification of Ac-225 and its daughters. Up to three TLCs per batch were processed in parallel to evaluate reproducibility and throughput. Results Digital autoradiography provided clear separation between bound and free fractions through two-dimensional count and temporal analysis. The ratio of bound-to-free activity decreased progressively and reached a stable plateau (≈ 2.1 %) after ∼100 min, consistent with transient equilibrium between Ac-225 and its short-lived daughters (Fr-221, At-217, Bi-213). Regulatory standards require a radiochemical purity ≥ 95 %; this threshold was accurately confirmed within only a few minutes of acquisition using digital autoradiography. Measured RCP values (≈98%) remained stable at equilibrium (≈ 97.9 ± 0.2 % by digital autoradiography vs 98 ± 2 % by phosphor imaging). Protocol optimization (drying, clean eluents, controlled spotting) ensured excellent reproducibility (CV < 1 %) and minimized artefacts. Simultaneous analysis of three samples reduced per-sample time and supported parallel QC for preclinical batches. Conclusion iTLC digital autoradiography combined with temporal fitting provides reliable within-one-hour RCP assessment for Ac-225 radiopharmaceuticals. The method offers fast, non-destructive and reproducible QC validated against a reference phosphor-imaging approach, accelerating preclinical workflows and supporting standardized development of TAT agents. This sub-hour QC reduces release time from 12–24 h to < 1 h, offering a major operational advantage for preclinical and translational production. Funding Acknowledgements This work was supported by the LabCom AIDA (ANR-23-LCV1-0003-01), funded by the French National Research Agency (ANR) and the “Région Pays de la Loire” (Project TN_2024_LABCOM_AIDA_Lab_GLISSANDO).

Introduction Digital autoradiography enables micrometric visualization of alpha-emitter distributions in preclinical tissues. Beyond quantitative activity mapping, offline qualitative analysis provides complementary information in energy, time, and spatial domains, essential for interpreting heterogeneous dose deposition and daughter redistribution in targeted alpha therapy. Such approaches improve biological interpretability and reproducibility in alpha-emitter dosimetry. Objectives To identify and illustrate how offline analytical methods enhance the interpretative and translational value of digital autoradiography for alpha-emitter dosimetry. Materials and Methods Digital acquisitions were performed using high-resolution alpha-imaging systems and multi-channel spectroscopic detectors. Offline workflows were evaluated through five analytical domains: (1) energy-resolved analysis to discriminate isotopic signals (e.g., parent and daughter alpha emitters) and suppress background; (2) time-resolved imaging to reconstruct decay kinetics and transient equilibria; (3) spatial and morphological analysis to describe heterogeneous uptake within tissues; (4) image co-registration with microscopy for biological correlation; and (5) computational modeling to integrate spatial data into microdosimetric and radiobiological frameworks. Each domain was assessed for its contribution to data interpretability and reproducibility. Results Offline analysis enhanced isotopic discrimination, temporal and spatial visualization of redistribution patterns, and biological correlation through co-registration. Combined with computational modeling, these methods connected autoradiographic patterns to absorbed-dose heterogeneity, transforming digital autoradiography from a static imaging tool into a multidimensional interpretive platform. Conclusion Offline analytical workflows substantially improve the interpretive power of digital autoradiography. By integrating energy, temporal, spatial, and biological information, they reinforce the link between activity distribution, dose deposition, and tissue response, strengthening the translational value of preclinical dosimetry in targeted alpha therapy. Funding Acknowledgements This work was supported by the LabCom AIDA (ANR-23-LCV1-0003-01), funded by the French National Research Agency (ANR) and the “Région Pays de la Loire” (Project TN_2024_LABCOM_AIDA_Lab_GLISSANDO).

Radioactive particles often contain very high radioactivity concentrations and are widespread. They pose a potential risk to human health and the environment. Their detection, quantification, and characterization are crucial if we are to understand their impact. Here, we present the use of a real-time autoradiography gaseous detector (using parallel ionization multiplier) to expedite and improve the accuracy of radioactive particle screening in complex environmental samples. First, standard particles were used to assess the detector capabilities (spatial resolution, spectrometry, and artefact contributions), then, we applied the technique to more complex and environmentally relevant samples. The real-time autoradiography technique provides data with a spatial resolution (≲100 µm) suitable for particle analysis in complex samples. Further, it can differentiate between particles predominantly emitting alpha and beta radiation. Here, the technique is applied to radioactive cesium-rich microparticles collected from the Fukushima Daiichi nuclear exclusion zone, showing their accurate detection, and demonstrating the viability of real-time autoradiography in environmental scenarios. Indeed, for more complex samples (radioactive particles in a less radioactive heterogeneous background mix of minerals), the technique permits relatively high selectivity for radioactive particle screening (up to 61.2% success rate) with low false positive percentages (~ 1%).

As part of translational research projects, mice may be irradiated on radiobiology platforms such as the one at the ARRONAX cyclotron. Generally, these platforms do not feature an integrated imaging system. Moreover, in the context of ultra-high dose-rate radiotherapy (FLASH-RT), treatment planning should consider potential changes in the beam characteristics and internal movements in the animal.A patient-like set-up and methodology has been implemented to ensure target coverage during conformal irradiations of the brain, lungs and intestines. In addition, respiratory cycle amplitudes were quantified by fluoroscopic acquisitions on a mouse, to ensure organ coverage and to assess the impact of respiration during FLASH-RT using the 4D digital phantom MOBY. Furthermore, beam incidence direction was studied from mice µCBCT and Monte Carlo simulations. Finally,in vivodosimetry with dose-rate independent radiochromic films (OC-1) and their LET dependency were investigated.The immobilization system ensures that the animal is held in a safe and suitable position. The geometrical evaluation of organ coverage, after the addition of the margins around the organs, was satisfactory. Moreover, no measured differences were found between CONV and FLASH beams enabling a single model of the beamline for all planning studies. Finally, the LET-dependency of the OC-1 film was determined and experimentally verified with phantoms, as well as the feasibility of using these filmsin vivoto validate the targeting.The methodology developed ensures accurate and reproducible preclinical irradiations in CONV and FLASH-RT without in-room image guidance in terms of positioning, dose calculation andin vivodosimetry.

Cesium-134 and -137 are prevalent, long-lived, radio-toxic contaminants released into the environment during nuclear accidents. Large quantities of insoluble, respirable Cs-bearing microparticles (CsMPs) were released into the environment during the Fukushima Daiichi nuclear accident. Monitoring for CsMPs in environmental samples is essential to understand the impact of nuclear accidents. The current detection method used to screen for CsMPs (phosphor screen autoradiography) is slow and inefficient. We propose an improved method: real-time autoradiography that uses parallel ionization multiplier gaseous detectors. This technique permits spatially resolved measurement of radioactivity while providing spectrometric data from spatially heterogeneous samples-a potential step-change technique for use after nuclear accidents for forensic analysis. With our detector configuration, the minimum detectable activities are sufficiently low for detecting CsMPs. Further, for environmental samples, sample thickness does not detrimentally affect detector signal quality. The detector can measure and resolve individual radioactive particles ≥465 μm apart. Real-time autoradiography is a promising tool for radioactive particle detection.

Purpose The ARRONAX cyclotron facility offers the possibility to deliver proton beams from low to ultra-high dose rates (UHDR). As a good control of the dosimetry is a prerequisite of UHDR experimentations, we evaluated in different conditions the usability and the dose rate dependency of several radiochromic films commonly used for dosimetry in radiotherapy. Methods We compared the dose rate dependency of three types of radiochromic films: GAFchromic (TM) EBT3 and GAFchromic (TM) EBT-XD (Ashland Inc., Wayne, NJ, USA), and OrthoChromic OC-1 (OrthoChrome Inc., Hillsborough, NJ, USA), after proton irradiations at various mean dose rates (0.25, 40, 1500, and 7500 Gy/s) and for 10 doses (2-130 Gy). We also evaluated the dose rate dependency of each film considering beam structures, from single pulse to multiple pulses with various frequencies. Results EBT3 and EBT-XD films showed differences of response between conventional (0.25 Gy/s) and UHDR (7500 Gy/s) conditions, above 10 Gy. On the contrary, OC-1 films did not present overall difference of response for doses except below 3 Gy. We observed an increase of the netOD with the mean dose rate for EBT3 and EBT-XD films. OC-1 films did not show any impact of the mean dose rate up to 7500 Gy/s, above 3 Gy. No difference was found based on the beam structure, for all three types of films. Conclusions EBT3 and EBT-XD radiochromic films should be used with caution for the dosimetry of UHDR proton beams over 10 Gy. Their overresponse, which increases with mean dose rate and dose, could lead to non-negligible overestimations of the absolute dose. OC-1 films are dose rate independent up to 7500 Gy/s in proton beams. Films response is not impacted by the beam structure. A broader investigation of the usability of OC-1 films in UHDR conditions should be conducted at intermediate and higher mean dose rates and other beam energies.

Cesium-134 and -137 are prevalent long-lived, radio-toxic contaminants released into the environment from the nuclear industry. During nuclear accidents, large quantities of 134+137Cs-bearing micro-particles can be released into the atmosphere and transported over large distances. Monitoring particulate 134+137Cs in environmental samples is essential to understand the impact of nuclear accidents. However, the current detection method used to screen for Cs-containing micro-particles in samples (phosphor screen autoradiography) is slow and inefficient. Here, we propose a new method to detect 134+137Cs microparticles: real-time autoradiography with parallel ionization multiplier gaseous detectors. This technique permits spatially resolved measurement of radioactivity and provides spectrometric data in real-time from spatially heterogenous samples—a step-change in nuclear accident response and nuclear forensics. With our detector configuration, we found that the minimum detectable activities for Cs-134 (0.95 mBq/mm2) and Cs-137 (1.02 mBq/mm2) are sufficiently low for detecting Cs micro-particles emitted from nuclear accidents. We investigated how sample thickness impacts data collection: for environmental samples, thickness does not detrimentally affect detector signal quality. Furthermore, the detector can measure and resolve individual radioactive particles separated by ≥465 µm. Our research establishes real-time autoradiography as a promising tool for radioactive particle detection in complex environmental samples (e.g., soils, air filters, etc.).

Proton therapy (PRT) is an irradiation technique that aims at limiting normal tissue damage while maintaining the tumor response. To study its specificities, the ARRONAX cyclotron is currently developing a preclinical structure compatible with biological experiments. A prerequisite is to identify and control uncertainties on the ARRONAX beamline, which can lead to significant biases in the observed biological results and dose–response relationships, as for any facility. This paper summarizes and quantifies the impact of uncertainty on proton range, absorbed dose, and dose homogeneity in a preclinical context of cell or small animal irradiation on the Bragg curve, using Monte Carlo simulations. All possible sources of uncertainty were investigated and discussed independently. Those with a significant impact were identified, and protocols were established to reduce their consequences. Overall, the uncertainties evaluated were similar to those from clinical practice and are considered compatible with the performance of radiobiological experiments, as well as the study of dose–response relationships on this proton beam. Another conclusion of this study is that Monte Carlo simulations can be used to help build preclinical lines in other setups.