Advanced Luminescence Detectors in Radiotherapy and Nuclear Medicine

The application of ionizing radiation in medicine, both for diagnostics and in cancer therapy, requires precise monitoring and control of the radiation dose absorbed by the patient. Contemporary imaging and treatment techniques, such as proton radiotherapy, brachytherapy, or boron neutron capture therapy (BNCT), place increasingly high demands on dosimetry systems. Therefore, the primary objective of our project is to develop innovative composite fiber-optic detectors (FODs) that exploit scintillation phenomena and optically stimulated luminescence (OSL) for active, in situ radiation dosimetry under clinical conditions.

Project consortium

The project consortium consists of three teams with complementary expertise: Prof. Yuriy Zorenko from the Kazimierz Wielki University (UKW) in Bydgoszcz (project coordinator), Prof. Paweł Bilski from the Institute of Nuclear Physics of the Polish Academy of Sciences in Kraków, and Prof. Andrzej Suchocki from the Institute of Physics of the Polish Academy of Sciences in Warsaw.

On the UKW side, the project also involves the teams of Dr. Janusz Winiecki and Dr. Mateusz Wędrowski from the Oncology Centre in Bydgoszcz, where  testing of the developed FOD detectors will be conducted.

Professor Y. Zorenko, Prof. P. Bilski and Prof. A. Suchocki in the technological and research laboratories, from left: Department of Optoelectronic Materials at UKW in Bydgoszcz, Institute of Nuclear Physics of the Polish Academy of Sciences in Kraków and Institute of Physics of the Polish Academy of Sciences in Warsaw.

Materials and methods

The project focuses on research into new luminescent materials, including crystals, thin single-crystalline films, and composite film-crystal structures based on oxide compounds. The materials under study include, among others, heavy mixed (Y,Lu)₃(Al,Ga,Sc)₅O₁₂ garnets, (Y,Lu)AlO₃ perovskites, as well as tissue-equivalent MgAl₂O₄ spinel and Al₂O₃ sapphire, containing dopants of rare-earth ions (Ce, Pr) and transition metals (Mn).

Composite detectors will be created using the liquid-phase epitaxy (LPE) growth method – a technology that enables the precise deposition of thin-film structures onto crystalline substrates. This method has already been successfully employed by the UKW project team to create composite luminescent materials for optoelectronic applications (Fig. 2, left).

Principle of detector operation

The designed detectors will have a multilayered structure, consisting of several functional layers of materials with varied luminescent properties. The purpose of this design is to enable the simultaneous detection of different components of mixed ionizing radiation beams, including X-rays and gamma rays, electrons, protons, neutrons, alpha particles, and ions. The primary challenge is to effectively separate signals originating from various detector layers after absorption of  different types of radiation.

We intend to achieve this by analysing differences in radioluminescence spectra (Fig. 2), as well as by studying variations in the OSL signal decay kinetics of the individual layers and the substrate. This approach enables for the selective analysis of signals from each layer, allowing for a significantly more precise measurement of both the composition and intensity of the radiation.

RFig. 1. Secondary nuclear radiation in BNCT therapy and a schematic of the proposed composite detector for measuring the dose from various types of ionising radiation (⁷Li ions, α-particles, and γ-rays)

Novelty and scientific significance

A key innovative aspect of the project is utilization of scintillation phenomena in the design of FOD detectors, as well as the application of scintillation parameters of the materials, such as emission spectra and light yields, for  direct in-situ measurement of radiation dose. It is essential that the radioluminescence signal remains linear with respect to dose over a wide range of values and that the individual layers emit light with characteristic spectra, allowing for their unambiguous differentiation.

In addition to scintillation properties, it is also essential to utilise the phenomenon of infrared-stimulated luminescence (IRSL), which has been recently observed in cerium-doped garnets (GAGG:Ce, YAG:Ce, LuAG:Ce). These materials exhibit very high sensitivity, enabling detection of doses on the order of micrograys. Similarly, promising IRSL properties have been observed in Pr³⁺ doped and Mn²⁺ doped perovskites as well as in MgAl₂O₄ spinel with selected dopants. The combination of their properties along with the possibility of creating layered structures using the LPE method, opens up new prospects for  designing composite detectors.

Basic research and applied experiments

In parallel with the work on detector design, in-depth studies will be conducted on the mechanisms responsible for IRSL and OSL phenomena. Although it is known that the emission of the materials mainly originates from dopant ions Ce³⁺ and Pr³⁺ or Mn2+, little is known about the nature of the charge traps. It is assumed that structural defects, such as oxygen vacancies or antisite defects, may play a significant role in this process. The project will include studies employing advanced spectroscopic techniques, such as synchrotron radiation, high-pressure spectroscopy, and band-gap engineering, aimed at identifying trap centres and elucidating the mechanisms of energy storage and transfer in the investigated materials.

Clinical applications

In the final phase of the project, applied studies will be conducted – the detectors will be tested under real clinical conditions at the Oncology Centre in Bydgoszcz (Fig. 3). They are planned for use in therapeutic practice, including boron neutron capture therapy (BNCT), proton therapy and brachytherapy, as well as in the monitoring of radiation from liquid radioactive sources and medical waste.

On the left: Prof. Y. Zorenko and Dr J. Winięcki – Head of the Medical Physics Department at the Oncology Centre in Bydgoszcz – in a treatment room during testing of a fibre-optic detector prototype for X-ray dose measurement in a teletherapy procedure. On the right: project team members from the Oncology Centre in Bydgoszcz – Dr J. Winięcki, M.Sc. B. Sobeich and P. Michalska.

Summary

The project combines advanced basic research with direct clinical applications, aiming to develop innovative multilayer luminescent detectors for active dosimetry in medicine. The results of this work will contribute not only to enhancing the safety and precision of therapies using ionizing radiation but also to advancing the understanding of fundamental physical phenomena occurring in modern luminescent materials.