Development of Microdosimetric Detectors for Radiobiology in Hadron Therapy

by Cristiana Rodrigues (LIP/FCUL)

Thursday 15 Oct 2026, 11:30 → 13:00 Europe/Lisbon

LIP-Lisboa/3-311 - Sala de Seminários (LIP Lisboa)

Microscale characterization of radiation fields in hadron therapy requires detectors capable of combining high dose sensitivity with high spatial resolution. This work explored two approaches to develop cost-effective materials for active and passive dosimetry in radiobiology: production of micrometric plastic optical fibers (mPOFs) for active dosimeters; and growth of α-Al₂O₃ crystals for luminescence dosimetry and particle tracking. 

Fiber-based microdosimetry requires micrometer-thick fibers with dimensions close to typical cell sizes. However, the smallest mPOFs available have a 200 μm diameter. Three production methods were studied with an in-house setup: electrospinning, melt-electrospinning, and melt-spinning. Melt-spinning delivered highly aligned fibers down to 80 μm. Process reproducibility was acceptable, with diameter tolerances within 30% and optical transmission comparable to that of commercial POFs. 

Luminescence-based detectors are particularly attractive as thermoluminescence (TL) and optically stimulated luminescence (OSL) provide high low-dose sensitivity, whereas fluorescent nuclear track detectors (FNTDs) enable visualization of individual charged-particle tracks with subcellular resolution. α-Al₂O₃ single crystals were grown by the flux-evaporation method, with a Li₂O–MoO₃ system. Standard C, {C,Mg} doping and novel combinations {C,Zn}, {C,Ti}, {C,Mn}, {C,Ce} and {C,Si} were investigated. The radiation-induced luminescence (30 mGy – 15 Gy) to ⁹⁰Sr/⁹⁰Y β-radiation were studied as a function of precursor purity and doping. Increasing MoO₃ and Al₂O₃ precursor purity enhanced TL and OSL intensity by up to 67× and 14×, respectively, and significantly improved low-dose sensitivity. {C,Mg} and {C,Mn(IV)} yielded the strongest TL/OSL responses, with up to a twofold TL and fourfold OSL intensity increase relative to undoped crystals. The FNTD potential of flux-grown crystals was assessed through ¹²C-ion irradiations conducted at the Heidelberg Ion-Beam Therapy Center (HIT, Germany). Both undoped and {C,Mg}-doped crystals exhibited ion tracks. {C,Mg} samples showed improved performance, with approximately 50% detection of expected tracks, although remaining less sensitive than commercial Czochralski-grown FNTDs. These results demonstrate the potential of flux-grown Al₂O₃ as a low-cost material for luminescence dosimetry and track detection, motivating further optimization of crystal growth.