Integrating a Tool to Automatically Determine Necessity of Online Adaptive Replanning

PURPOSE/OBJECTIVE(S)

As online adaptive replanning (OLAR) is labor-intensive and time-consuming, it's desirable to determine when OLAR is necessary before OLAR is initiated. We have previously reported a novel method to automatically determine the necessity of OLAR using machine leaning algorithms based on the structural similarity maps (SSIM) and wavelet texture maps (WMT) extracted from the daily MRI during MR-guided adaptive radiation therapy (MRgART). This study aims to integrate this method into a commercial software platform that has been used during our routine MRgART.

MATERIALS/METHODS

The method of automatically determining the necessity of OLAR based on daily MRI was implemented and integrated into the software platform through a specifically developed workflow. The obtained workflow was tested using 25 daily MRI sets acquired from 5 patients with pancreatic cancer in the following procedure: 1) rigidly registering the daily and reference MRIs, 2) identifying the region enclosed by the 50-100% iso-dose surfaces on the daily MRI by transferring the iso-dose surfaces from the reference to the daily MRIs, 3) launching our in-house codes to calculate significant changes in textures extracted from SSIM and WMT maps, 4) inputting the feature values into the pre-trained classifier models for SSIM and WMT, and 5) outputting results considering the WMT based prediction as the primary indicator and the SSIM-based as the secondary (validation) indicator on whether OLAR is needed for the daily MRI.

RESULTS

The execution of the developed workflow was fast and can be used to streamline the process. It provides the ability to scroll through the images for better decision making while providing quantitative prediction within 30-38 seconds. Eighty percent of the daily MRIs required OLAR. The SSIM map displayed was able to successfully captured the areas of similarity between the reference and daily MRIs and the WMT prediction agreed with the prediction class.

CONCLUSION

The integration of the prediction method for automatically determining the necessity of OLAR based on two independent machine learning classifiers into a commercially available software is feasible and can be used to streamline the process of MRgART. With larger verification studies, this workflow-based tool may be developed into a generalized tool that assist in OLAR using different platforms.

Influence of Shell Formation on Morphological Structure, Optical and Emission Intensity on Aqueous Dispersible NaYF4:Ce/Tb Nanoparticles

A highly water-dispersible NaYF4:Ce/Tb (core), NaYF4:Ce/Tb@NaYF4(core/shell) and NaYF4:Ce/Tb@NaYF4@SiO2 (core/shell/SiO2) nanoparticles (NPs) were synthesized via a general synthesis approach. The growth of an inert NaYF4 and silica shell (~14 nm) around the core-NPs resulted in an increase of the average size of the nanopaticles as well as broadening of their size distribution. The optical band-gap energy slightly decreases after shell formation due to the increase the crystalline size. To optimize the influence of shell formation a comparative analysis of photoluminescence properties (excitation, emission, and luminescence decay time) of the core, core/shell, and core/shell/SiO2 NPs were measured. The emission intensity was significantly enhanced after inert shell formation around the surface of the core NPs. The Commission International de l'Eclairage chromaticity coordinates of the emission spectrum of core, core/shell, core/shell/SiO2 NPs lie closest to the standard green color emission at 545 nm. By quantitative spectroscopic measurements of surface-modified core-NPs, it was suggested that encapsulation with inert and silica layers was found to be effective in retaining both luminescence intensity and dispersibility in aqueous environment. Considering the high aqueous dispersion and enhanced luminescence efficiency of the core-NPs make them an ideal luminescent material for luminescence bioimaging and optical biosensors.

Enhanced up-conversion and temperature-sensing behaviour of Er(3+) and Yb(3+) co-doped Y2Ti2O7 by incorporation of Li(+) ions

Y2Ti2O7:Er(3+)/Yb(3+) (EYYTO) phosphors co-doped with Li(+) ions were synthesized by a conventional solid-state ceramic method. X-ray diffraction studies show that all the Li(+) co-doped EYYTO samples are highly crystalline in nature with pyrochlore face centred cubic structure. X-ray photon spectroscopy studies reveal that the incorporation of Li(+) ions creates the defects and/or vacancies associated with the sample surface. The effect of Li(+) ions on the photoluminescence up-conversion intensity of EYYTO was studied in detail. The up-conversion study under ∼976 nm excitation for different concentrations of Li(+) ions showed that the green and red band intensities were significantly enhanced. The 2 at% Li(+) ion co-doped EYYTO samples showed nearly 15- and 8-fold enhancements in green and red band up-converted intensities compared to Li(+) ion free EYYTO. The process involved in the up-conversion emission was evaluated in detail by pump power dependence, the energy level diagram, and decay analysis. The incorporation of Li(+) ions modified the crystal field around the Er(3+) ions, thus improving the up-conversion intensity. To investigate the sensing application of the synthesized phosphor materials, temperature-sensing performance was evaluated using the fluorescence intensity ratio technique. Appreciable temperature sensitivity was obtained using the synthesized phosphor material, indicating its applicability as a high-temperature-sensing probe. The maximum sensitivity was found to be 0.0067 K(-1) at 363 K.

Influence of Gd3+ co-doping on structural property of CaMoO4:Eu nanoparticles

A facile auto-combustion route is used for the synthesis of Gd(3+) (2, 5, 7 and 10 at%) co-doped CaMoO4:Eu nanoparticles. X-ray diffraction study suggests that as-prepared samples have extra impurity phases in addition to main tetragonal phase of CaMoO4, and such extra phases decrease as the annealing temperature increases from 600 to 900 °C. The crystal structure has been analysed using Rietveld program. It has space group I4₁/a (88) and Z = 4 (number of CaMoO4 formula units per unit cell). Average crystallite sizes of as-prepared, 600 and 900 °C annealed samples for 2 at% Gd(3+) are found to be ~33, 48 and 61 nm, respectively. The lattice strains of 5 at% Gd(3+) co-doped CaMoO4:Eu for as-prepared and 900 °C are 0.001 and 0.002, respectively. Fourier transform infrared spectroscopy gives the absorption bands at ~815 and 427 cm(-1), which are related to asymmetric stretching and bending vibrations of MoO4(2-) tetrahedron. Particle morphology is studied using scanning and transmission electron microscopy (SEM and TEM), and aggregation of particles is found. X-ray photoelectron spectroscopy (XPS) is utilized to examine the oxidation states of metal ions/oxygen and oxygen ion vacancies in Gd(3+) co-doped CaMoO4:Eu. With an increase in Gd(3+) concentration, peaks corresponding to the Gd(3+) (2p(3/2) and 2p(5/2)) binding energy could be detected.

Enhanced photoluminescence in CaMoO4:Eu3+ by Gd3+ co-doping

We have studied the luminescence property of CaMoO4:Eu(3+). The emission peaks at 590 ((5)D0→(7)F1) and 613 nm ((5)D0→(7)F2) for Eu(3+) are observed after excitation at 266 nm (i.e. Mo-O charge transfer band). The peak intensity of the latter dominates over the former indicating an asymmetric environment of Eu(3+) in EuO8 polyhedron or parity mixing. Luminescence intensity increases significantly with co-doping of Gd(3+). This is ascribed to energy transfer from Mo-O/Gd(3+) to Eu(3+). Luminescence intensity increases with annealing up to 900 °C due to the extent of decrease of non-radiative rates. Very high asymmetric values (A21) of 12-16 are found indicating a red emitter. As-prepared samples are dispersible in polar solvents like water, ethanol, methanol, dimethyl sulfoxide (DMSO) and ethylene glycol (EG); and among them, optimum luminescence is found in methanol. Polymer film shows red emission. The quantum yields of as-prepared 2 and 10 at% Gd(3+) co-doped CaMoO4:Eu(3+) under 277 nm (UV excitation) are 21 and 80%, respectively.

Effect of surface coating on optical properties of Eu(3+)-doped CaMoO4 nanoparticles

A simple polyol method has been used for the synthesis of CaMoO4:Eu (core), CaMoO4:Eu@CaMoO4 (core/shell) and their silica coated CaMoO4:Eu@CaMoO4 (core/shell/shell) nanoparticles. X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), UV/Vis absorption and photoluminescence (PL) spectroscopies techniques has been employed for their characterization. XRD patterns and FT-Raman spectra showed that these nanoparticles have a scheelite-type tetragonal structure without the presence of deleterious phases. These nanoparticles were easily dispersed in water, producing a transparent colloidal solution. The optical energy band-gap decreases after core/shell formation due to increase the crystalline size. The photoluminescence (PL) spectra of the as-synthesized core, core/shell and core/shell/shell nanoparticles measured with an excitation source wavelength of 325nm showed that the emission intensity was increases after shell formation around the surface of core nanoparticles.

Enhanced luminescence of CaMoO₄:Eu by core@shell formation and its hyperthermia study after hybrid formation with Fe₃O₄: cytotoxicity assessment on human liver cancer cells and mesenchymal stem cells

Highly water dispersible Eu³⁺ doped CaMoO₄ nanoparticles (core) covered by CaMoO₄ (shell) have been prepared using the polyol method. Significant enhancement in luminescence intensity by core@shell formation is observed due to the decrease of non-radiative rate arising from surface/defect of particles. Effect of 266 nm laser excitation (Mo-O charge transfer band) on the asymmetric ratio (A₂₁ = intensity ratio of electric to magnetic dipole transitions) has been studied and compared with a xenon lamp source. Luminescence intensity increases with the increase of power at 532 nm laser excitation. In order to explore materials, which can show dual functionalities such as luminescence as well as magnetic properties (magnetization of ∼14.2 emu g⁻¹), water dispersible Fe₃O₄-CaMoO₄:Eu hybrid magnetic nanoparticles (MN) have been prepared. This shows good heating ability up to ∼42 °C (hyperthermia) and luminescence in the red region (∼612 nm), which is in a biological window (optical imaging). Biocompatibility of the synthesized Fe₃O₄-CaMoO₄:Eu hybrid magnetic nanoparticles has been evaluated in vitro by assessing their cytotoxicity on human liver cancer cells (HepG2 cells) and hTERT cells using the MTT assay and fluorescent microscopy studies.

In-vitro cyto-toxicity, geno-toxicity, and bio-imaging evaluation of one-pot synthesized luminescent functionalized mesoporous SiO2@Eu(OH)3 core-shell microspheres

Luminescent functionalized mesoporous SiO2@Eu(OH)3 core-shell microspheres (LFMCSMs) were prepared by coating of europium hydroxide (Eu(OH)3) shell on mesoporous silica (SiO2) nanospheres via a facile one-pot process at low temperature. The FETEM images revealed that a well-defined luminescent europium hydroxide shell was successfully grafted on the surface of mesoporous silica nanospheres. These experimental results showed that the LFMCSM has a typical diameter of ca. 392 nm consisting of the silica core with about 230 nm in diameter and europium hydroxide shell with an average thickness of about 162 nm. LFMCSMs exhibited strong red emission peak upon irradiation with ultraviolet light, which originated from the electric-dipole transition (5)D0 → (7)F2 (614 nm) of Eu(3+) ion. The biocompatibility of the synthesized LFMCSMs was evaluated in vitro by assessing their cytotoxic and genotoxic effect on human hepatoblastoma (HepG2) cells using MTT, TUNEL, fluorescent staining, DNA ladder and Gene expression assays respectively.

FROM THE CLINICAL EDITOR

This paper describes the development of a one-pot synthesis of luminescent mesoporous SiO2@Eu(OH)3 core-shell microspheres and evaluates their favorable in vitro cyto-toxicity and geno-toxicity, and their applications in bio-imaging of these particles that emit bright red signal under UV exposure.