(Tuesday, 7/31/2018) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 4
Purpose: X-ray-stimulated photodynamic therapy (X-PDT) is a burgeoning therapeutic modality that involves the use of radioluminescent nanomaterials as transducers to accomplish excitation of traditional photosensitizer molecules, circumventing the light penetration issues encountered with conventional PDT. The efficiency of an X-PDT system is expected to depend on several physical parameters of the nanomaterials involved, including radioluminescence yields, the determination of which will assist in the design of such systems.
Methods: We have synthesized and characterized a variety of new nanoparticles in the range of 13 to 50 nm, with the general composition β-NaLnF₄, incorporating known luminescent activator/sensitizer pairs. Using Monte Carlo modeling to complement luminescence measurements of nanoparticle suspensions and a reference liquid scintillator under orthovoltage x-ray excitation, we quantified in absolute terms the radioluminescence yields and intrinsic conversion efficiencies of the colloidally-dispersed nanoparticles.
Results: Distinct radioluminescence was observed from 4f-4f transitions of Gd³�, Tb³�, and Eu³� activators, spanning UV-B to NIR wavelengths. Colloidal β-NaLuF₄:Gd³�,Tb³� in toluene displayed the strongest output at 39,460 photons/MeV absorbed, comparable to some of the best non-hygroscopic bulk crystal scintillators and x-ray phosphors such as Gd₂O₂S:Tb. Other compositions displayed moderate light yields: β-NaLuF₄:Gd³�,Eu³� ranged from 5460 ph/MeV absorbed to 11670 ph/MeV absorbed, and β-NaLuF₄:Gd³�,Ce³� produced 7190 ph/MeV absorbed. Selected samples were made water-dispersible by polymer coating and conjugated to photosensitizer molecules. Preliminary results demonstrating the efficacy of an X-PDT system are presented.
Conclusion: X-PDT shows promise as a means to augment existing radiotherapy treatments. Due to the variety of materials under investigation, quantitative comparisons remain difficult. We have developed a generalized approach for determining radioluminescence yields of colloidal nanoparticles, intended to foster comparisons between systems and assist with optimization through identification of bottlenecks.
Funding Support, Disclosures, and Conflict of Interest: Funding support from: CIHR Operating Grant FRN #133500 CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (grant number: 432290)
Keywords
PDT, Fluorescence, Scintillators
Taxonomy
Not Applicable / None Entered.
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