Kathriarachchi, Vindu

The purpose of the study is to investigate the effect of preparation temperature on the
crystal structure and magnetic properties of nanophase Fe-substituted Hydroxyapatite. Multisubstituted
Hydroxyapatite (HAp), Ca5(PO4)3OH, is the main mineral phase in physiological
apatite, ~70 wt% in bones and dentin, and ~96 wt% in enamel. Iron is one of the minor
substitution elements (0.01-0.1 wt% in bone and 0.003 wt% in enamel) replacing Ca in the HAp
structure. Research interest on Fe-HAp is related to the fact that Fe for Ca substitution reduces
the solubility of HAp therefore it functions as a cavities preventive agent. In contrast, Fe
overload causes a decrease in bone mechanical strength. Furthermore, Fe-HAp can find
applications in hyperthermia based anti-cancer treatments and in magnetic resonance imaging
(MRI) contrast agents. Two sets of Ca5-xFex(PO4)3OH samples (x=0,0.05,0.1,0.2,0.3) were
synthesized by a chemical precipitation method at physiological temperature (370C) and 800C.
The samples were calcinated at 6500C and deuterated at 6000C. The samples were characterized
by x-ray powder diffraction (XRD), neutron powder diffraction (NPD) and SQUID
Magnetometry. A single-phase system was detected for nominal iron content x≤0.1 by XRD
phase identification in both sets of samples, while hematite (α-Fe2O3) and/or maghemite (γ-
Fe2O3) develops starting at x=0.1. According to the magnetic measurements, sample with x=0
showed diamagnetic behavior while samples with Fe showed paramagnetic behavior. Combined
Rietveld refinements of XRD and NPD patterns will provide accurate information on the effect
of processing temperature on the crystallographic parameters of the nano-materials.

The effect of processing temperature on the crystal structure properties of the Fe-substituted Hydroxyapatite (Fe-HAp) was studied by using the Rietveld refinement method of powder x-ray (XRD) and neutron diffraction (NPD) patterns. Superconducting QUantum Interference Device (SQUID) magnetometry, transmission electron microscopy (TEM) and x-ray fluorescence spectroscopy (XRF) were used to study the magnetic properties, particle morphology and chemical composition of the prepared samples. Two sets of samples of chemical formula Ca5-xFex(PO4)3OH were prepared with x = 0, 0.05, 0.1, 0.2 and 0.3 by using processing temperatures of 37°C and 80°C, following a two-step co-precipitation method. A single phase HAp was identified in samples with x = 0 and 0.05. Processing temperature affects the type and percentage of secondary phases: hematite was detected in samples prepared at 37°C with x ≥ 0.1, hematite and maghemite were detected in samples prepared at 80°C with x = 0.2 and 0.3. Rietveld refinements of NPD and XRD patterns showed that the a lattice constants are greater in Fe-substituted samples prepared at 37°C, whereas the c lattice constants are greater in the 80°C samples for x ≥ 0.05. Fe preferentially substitutes at the Ca2 site in the 80°C samples, whereas Ca1 is the preferred substitution site in the 37°C samples. Fe substitution results to a decrease of the lattice constants at both preparation temperatures. The ratios Fe/(Fe + Ca) of the refined atomic fractions of the samples prepared at 80°C are greater than those of the 37°C samples. Further, more secondary phases form in samples prepared at 37°C compared to 80°C samples. The magnetic measurements reveal that pure HAp is diamagnetic, whereas samples with x = 0.05 and 0.1 are paramagnetic. Samples with x = 0.3 showed superparamagnetic behavior based on ZFC and FC measurements. Similar hysteresis loops in samples x = 0.2 and 0.3 indicate that the samples with x = 0.2 may show superparamagnetic properties. For x = 0.2 and 0.3, the samples prepared at 80°C showed higher magnetization compared to the 37°C samples, because of the maghemite secondary phase. Based on the TEM images, Fe substituted HAp nanoparticles prepared at 37°C are mainly spherically shaped, and the 80°C particles are mainly elongated. Increase of the Fe concentration favors formation of elongated particles and larger spherical particles. The XRF measurements confirm the Fe for Ca substitution in the HAp structure based on the decrease of the Ca/P and the increase of the Fe/(Fe + Ca) atomic ratios with the Fe concentration.

An improved method is introduced for prediction of local tumor control following lung
stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer
(NSCLC) patients using 18F-fluorodeoxyglucose positron emission tomography (18F-FDG
PET). A normalized background-corrected tumor maximum Standard Uptake Value
(SUVcmax) is introduced using the mean uptake of adjacent aorta (SUVref), instead of
the maximum uptake of lung tumor (SUVmax). This method minimizes the variations
associated with SUVmax and objectively demonstrates a strong correlation between the
low SUVcmax (< 2.5-3.0) and local control of post lung SBRT. The false positive rates
of both SUVmax and SUVcmax increase with inclusion of early (<6 months) PET scans,
therefore such inclusion is not recommended for assessing local tumor control of post
lung SBRT.