MO-A-213AB-05: Synthesis of High Quantum Yield Nano-Scintillators for Simultaneous Photodynamic Therapy in Radiotherapy

Purpose: Radioresistant tumors provide one of the biggest challenges for improving radiation therapy efficacy. We have demonstrated that semiconductor quantum dots can be used as ‘impedance matching’ devices converting high energy X-rays to visible photon range for a simultaneous and mechanistically independent treatment; photodynamic therapy (PDT). Application of quantum dots was limited by it toxicity and relatively low quantum yield with X-ray excitation. To further improve the combined therapy strategy, we synthesize and screen for safer and more efficient nanoparticles. Methods: Colloidal GdSe and Gd2O3 nanoparticles were synthesized in octadecene using octylamine and oleic acid as surfactants. The average diameter of the nanoparticles was 10 nm. The samples in organic solution was secured in a light tight box and irradiated by 300 kVp X-rays with a dose rate of 300 cGy/min. The visible photon yield is collected by a lens and transferred to the photomultiplier tube via optic fibers. The average photon counts for 100 seconds were compared between GdSe, Gd2O3 and CdSe quantum dots. Results: Different than quantum dots with fixed band gap and emission peaks, the fluorescent peaks of GdSe and Gd2O3 were excitation light dependent. Shorter emission wavelengths were resulted from higher incident photon energies but the spectra overlap well with the Soret band of porphyrin photosensitizers. While their fluorescence is substantially weaker compared with QDs under UV excitation, fluorescence from both GdSe and Gd2O3 is one order of magnitude stronger than that of QD when excited by 300 kV X-rays. Conclusions: Metal oxide nanoparticle scintillators are more efficient X-ray scintillators than Quantum dots. Moreover, Metal oxide nanoparticle can utilize the Soret band of photosensitizers for more effective energy transfer and excitation. These improvements will reduce the required radiation dose and drug concentration for simultaneous photodynamic therapy.