Online program Overview Session: MIC-21

Abstract

Targeted Alpha Therapy (TAT) requires dedicated imaging infrastructure capable of tracking alpha-emitting therapeutics and their daughters in vivo across a wide energy range. We present the experimental imaging performance of AlphaSPECT — a whole-body CZT-based clinical SPECT scanner comprising 32 detector panels integrating 512 micro-pinhole cameras in a dual field-of-view (FOV) configuration. Each panel integrates 16 CZT detectors (20×20×6 mm³, 500-μm pixel pitch) bump-bonded to HEXITEC ASICs. A CT-derived precision rotating gantry enables seamless switching between a large-FOV mode (5-mm pinholes, 40×40×20 cm³) and a high-resolution mode (2-mm pinholes, 20 cm spherical FOV), with sub-10-μm rotational accuracy. Energy calibration across all panels achieved 4–7 keV FWHM at 122 keV following charge-sharing correction. System response matrices were generated via voxel-driven ray-tracing, with geometry parameters estimated via nonlinear optimization against experimental point-source projections. Phantom reconstructions demonstrate uniform response across all detector panels and qualitative compartmental contrast in a 3D Hoffmann brain phantom (8 mCi Tc-99m, 30-minute acquisition), with resolution-limited blurring and partial-volume effects motivating investigation into angular sampling and reconstruction improvements. Ongoing studies include spatial resolution evaluation using a NEMA-compliant hot-rod phantom, collimator micro-rotation to enhance angular sampling, and joint dual-FOV reconstruction — to be presented at the conference.

Abstract

Boron Neutron Capture Therapy (BNCT) requires precise, real-time monitoring of the distribution of boron neutron capture reactions to maximize its therapeutic selectivity.

This work presents a major hardware evolution of the BeNEdiCTE detector, a SPECT-based system designed to track the 478 keV prompt gamma rays emitted during neutron capture.
The detector is based on a co-doped LaBr3(Ce, Sr) monolithic crystal read out by Silicon Photomultipliers.
The custom readout electronics have been entirely redesigned, utilizing boron-free substrates to eliminate background interference at 478 keV.
Furthermore, the new module features embedded AI on a high-performance FPGA for real-time reconstruction of interaction coordinates (X, Y, and Depth-of-Interaction) of the gamma rays on the scintillator.
To meet the high-flux demands of clinical BNCT, the dead time of the system has been reduced from 5.4 μs to 2.1 μs, and an hardware-based energy discrimination circuit has been designed to process only the small percentage of useful gamma rays across the whole spectrum.

We report on the system’s design and its upcoming validation at Nagoya University Accelerator-driven Neutron Source (Japan), marking the first SPECT measurement performed in a clinical-like facility.
Preliminary Monte Carlo simulations using a Derenzo-like phantom demonstrate the system’s high spatial resolution and its ability to distinguish lesion-sized volumes with boron concentrations as low as a few hundred ppm.
These results set the stage for the upcoming SPECT validation, which aims to prove the system's readiness for the non-invasive, live monitoring of boron distribution during clinical patient treatment.

Abstract

Targeted alpha therapy (TAT) has shown strong promise for cancer treatment because of its high linear energy transfer and localized cytotoxic effect. However, quantitative in-vivo imaging of TAT radiopharmaceuticals and its daughter remains challenging. The clinically administered activity is typically low, while the emitted gamma rays have low branching ratios, making conventional SPECT imaging sensitivity-limited and often requiring impractically long acquisition times. These limitations restrict accurate assessment of biodistribution, pharmacokinetics, and dosimetry, which are essential for optimizing TAT agents. This study investigates Compton imaging as a high-sensitivity alternative for visualizing TAT radiopharmaceuticals using a 5 cm × 5 cm single-layer 3D position-sensitive cadmium zinc telluride (CZT) camera. We performed a pilot imaging study with the alpha therapy radionuclide 225Ac in a clinical phantom filled with a low concentration of 6.2 kBq/mL surrounded by non-radioactive water. The phantom was scanned at 45^o rotational steps with 15-minute acquisitions each, and Compton images were reconstructed to evaluate source localization below clinically relevant low-activity conditions. This is the first time such a low-activity concentration has been imaged in a clinical phantom. The results demonstrate clear visualization of the radioactive inserts, supporting the feasibility of CZT-based Compton imaging for TAT monitoring. Based on these measurements, a multi-head configuration with at least eight detector modules could enable in-vivo imaging of ²²⁵Ac daughters of target organs within less than 30 minutes, and is being planned as the next step. Additional experiments with ²¹²Pb further suggest that the proposed approach can operate across a broad photon-energy range. Overall, this work provides experimental validation that compact 3D CZT Compton cameras may overcome key sensitivity barriers in alpha-emitter imaging and support future image-guided TAT.

Abstract

Lu-177, a promising theranostic radionuclide emitting β particles for therapy and γ photons for imaging, enables integrated diagnosis and therapy. Lu-177 imaging is increasingly important in treatments where imaging guides therapy. Previous work has demonstrated the use of scintillator as collimators to achieve simultaneous and separate imaging of F-18 and Tc-99m. In this work, we present a novel three-layer shared detector with variable collimator thickness, enabling simultaneous PET, SPECT, and Lu‑177 imaging. The first two crystal layers are perforated, with the top layer functioning as a low-energy high-sensitivity (LEHS) collimator, the top and middle layers combined acting as a low-energy high-resolution (LEHR) collimator and medium-energy general-purpose (MEGP) collimator. This design allows flexible adaptation for Tc‑99m and Lu‑177 imaging without hardware changes.A 96 mm-diameter system was simulated to evaluate two collimation schemes. Simulation results indicate that for Tc‑99m, the system can achieve both LEHS and LEHR imaging, with hot-rod phantom spatial resolution reaching 3.5 mm. For Lu‑177 (208 keV), inserting high-density LYSO or BGO in the middle layer improved peak-to-valley ratio compared to GAGG, and BGO yielded 4 mm spatial resolution for hot-rod phantom imaging. This flexible collimator design enhances detector versatility and offers a promising solution for multi-radionuclide theranostic applications. Future work will focus on optimizing collimator thickness and evaluating the performance of a prototype system.

Abstract

Conventional radiotherapy is a well-establish treatment for Non-Melanoma Skin Cancers (NMSCs). In this context, patient-specific quality assurance (PSQA) relies on accurate dose distribution measurements. However, current state-of-the-art technologies do not provide sufficient accuracy in assessing dose deposition within the superficial skin layers.
To compensate for the buildup effect in radiotherapy, a bolus material is commonly applied over the tumor to mimic tissue equivalence. Nevertheless, anatomical changes during treatment, such as tumor shrinkage, may introduce air gaps between the bolus and the skin, potentially leading to underdosage.
To address these limitations, a prototype detector, referred to as DQX, has been developed at Laboratoire de Physique Corpusculaire de Caen and experimentally evaluated at Centre François Baclesse . The device is based on a 100 μm thick plastic scintillator coupled to wavelength-shifting fibers and is designed to measure radiation dose in superficial tissue layers, targeting a relative measurement uncertainty below 1% for a 2 Gy photon beam at depths as shallow as 70 μm beneath the skin surface.
This contribution presents a comparison of the DQX prototype and a range of commonly used dosimetric devices employed in PSQA for conventional radiotherapy. These include tools such as ionization chambers and radiochromic films, each of which exhibits inherent limitations when applied to superficial dose measurements. The evaluation focuses on the response under possible clinical conditions such as air gaps variations. By benchmarking the DQX detector against these established technologies, this study also aims to assess its potential to improve dose verification in the buildup region.