arXiv subjects

Lars Eggimann

Publications and source records attributed to Lars Eggimann.

3 recordsLinked to original sources

arXiv2026

Terbium-149 PET/CT: First Quantitative Imaging with a Clinical Long-Axial Field-of-View Scanner

Introduction: Terbium-149 ($^{149}$Tb) is a promising radionuclide for targeted $α$ therapy that has a non-zero branching ratio (BR) for positron decay. However, its relatively low positron branching fraction and multiple prompt $γ$ emissions may challenge quantitative imaging. This study evaluates, for the first time, the imaging performance and quantitative accuracy of $^{149}$Tb using a clinical long axial field-of-view (LAFOV) PET/CT system. Methods: Quantitative accuracy of $^{149}$Tb was assessed with a NEMA IEC body phantom, which was filled with about 45 MBq $^{149}$Tb and a sphere-to-background ration of 10:1. The phantom was scanned for 20 min and shorter scan times and lower activities were simulated. Recovery coefficients, coefficient of variation, and lung residual error were evaluated for different reconstruction settings and compared to the EARL standard 2 for $^{18}$F. Results: High-quality PET images of $^{149}$Tb were obtained, even with a simulated total activity of 4.5 MBq. The 20 min and full activity scan yielded a mean recovery coefficient $RC_\textit{mean}$ of $0.55$, $0.69$, $0.73$, $0.76$, $0.79$, and $0.81$ for the six phantom spheres. Despite the low count statistics, the coefficient of variation stays mostly below $15\,\%$. Relative scatter correction combined with prompt $γ$ modeling provided robust quantification. Conclusion: $^{149}$Tb can be imaged using a commercial LAFOV PET/CT with a quantitative accuracy comparable to the EARL standard 2 for $^{18}$F. These findings demonstrate the feasibility of PET-based treatment verification and dosimetry for targeted $α$ therapy with $^{149}$Tb.

physics.med-ph↗

arXiv2026

Non-Destructive Beam Monitoring via Secondary Radiation Detection with Ce-Doped Silica Fibers

Non-destructive beam diagnostics are essential for low-energy medical cyclotrons, where even thin interceptive devices can severely degrade beam quality. We investigate an external fiber monitor (EFM) based on Ce-doped silica scintillating fibers that detects secondary radiation generated at existing beamline components of the 18 MeV Bern Medical Cyclotron beam transfer line (BTL). Three use cases were studied: (i) beam intensity monitoring around an electrically isolated, water-cooled beam dump; (ii) beam-loss monitoring around a 10 mm collimator under varying the beam focusing; and (iii) by steering a 6.5 mm $\times$ 6.5 mm beam spot on a beam dump. For case (i), the summed EFM signal exhibits a linear dependence on the current on target over nearly three orders of magnitude. In case (ii), a normalized EFM-based beam-loss proxy scales monotonically with an electrical loss proxy across several focusing settings. Furthermore, opposing-fiber signal ratios provide decoupled, monotonic sensitivity to horizontal and vertical beam displacements.

physics.ins-det↗

arXiv2025

Beam Energy Measurement using a Bayesian Approach with the Stacked Foil Method

We present a practical method to measure the energy of proton beams at a medical cyclotron using the stacked foil technique in combination with a Bayesian inference method. By measuring the $^{48}$V activity induced in a stack of irradiated titanium foils, the proton energy can be inferred without relying on direct current or charge measurements, making the method suitable even for low-vacuum environments or air-exposed setups. This technique is further extended to configurations where the beam energy is degraded to levels around 8 MeV. A Bayesian fit of the measured activity profile allows not only for a robust energy estimation but also for a consistent treatment of uncertainties and nuisance parameters. Monte Carlo simulations are employed to validate the underlying assumptions, including the impact of energy dispersion or cross-section uncertainties. Our results demonstrate that this method provides accurate beam energy measurements across several typical experimental setups used at the Bern Medical Cyclotron. Additionally, we evaluate the sensitivity of the method to the choice of nuclear cross-section data and assess how the number of foils in the stack affects the uncertainty in the inferred beam energy.

physics.acc-ph↗