Relative energy response of indigenously developed optically stimulated luminescence dosimeters Al2 O3 :C, LiMgPO4 :B and LiCaAlF6 :Eu,Y in therapeutic photon and electron beams.

The relative energy responses of three indigenously developed optically stimulated luminescence (OSL) phosphors in the disc form were studied in therapeutic photon and electron beams. Calibration in terms of absorbed dose was carried out in the dose range 5-500 cGy in 60 Co gamma rays, high energy X-rays, and electron beams used in radiotherapy. The combined standard uncertainty in the estimation of absorbed dose using these OSL discs (OSLDs) was 3.3%. Dose-response curves of these OSLDs in 60 Co gamma rays, 6 and 10 MV (flat and unflat), 15 MV and 6 and 15 MeV electron beams were found to be linear. Furthermore, these OSLDs exhibited a relative energy-dependent response for both photon and electron beams. The relative energy response correction factor for photon and electron beams were in the range 1.01-1.05 and 1.03-1.06, respectively.

Photoluminescence Studies of Rare Earth Doped Apatite Structured Phosphors.

We developed novel phosphors based on Y6Ba4(SiO4)6F2(YBSF) apatite doped with Dy3+. Phosphors with different doping concentrations of Dy3+ were prepared and their morphological, structural and spectral properties were analyzed. XRD pattern confirms the formation of Y6Ba4(SiO4)6F2 apatite structured phosphors with space group P63/m and Debye scherrer formula gives the average crystalline size 33.4 nm. The morphological and topographical studies were done by FESEM and HRTEM analysis. EDX spectra show presence of all initial reactants in the final product. Photoluminescence spectra show two prominent peaks at 487 nm and 573 nm corresponding to magnetic dipole transitions (4F9/2 → 6H15/2) and electric dipole transitions (4F9/2 → 6H13/2) for 350 nm excitation wavelength. The chromaticity coordinate of the prepared phosphors was found to be in the region of near white light which shows that prepared phosphor are potential single phased phosphor for white light emitting diodes.

Radiation dose measurements in a dental orthopantogram unit using indigenously developed optically stimulated luminescence dosimeters.

Dental orthopantogram (OPG)/cone beam computed tomography (CBCT) scanners are gaining popularity due to their 3D imaging with multiplanar view that provides clinical benefits over conventional dental radiography systems. Dental OPG/CBCT provides optimal visualization of adjacent overlaying anatomical structures that will be superpositioned in any single projection. The characteristics of indigenously developed optically stimulated luminescence dosimeters, namely, aluminium oxide doped with carbon (Al2 O3 :C), lithium magnesium phosphate doped with terbium and boron (LiMgPO4 :Tb,B) and lithium calcium aluminium fluoride doped with europium and yttrium (LiCaAlF6 :Eu,Y) were evaluated for their use in dental dosimetry. The dose-response of these dosimeters was studied at X-ray energies 60 kV, 70 kV and 81 kV. Radiation doses were also measured using Gafchromic film for comparison. Radiation dose was measured at eight different locations of a polymethyl methacrylate (PMMA) head phantom including eyes. The optically stimulated luminescence (OSL) sensitivity of LiMgPO4 :Tb,B is about 1.5 times and LiCaAlF6 :Eu, is about 20 times higher than the sensitivity of Al2 O3 :C. It was found that measured radiation doses by the three optically stimulated luminescence dosimeters (OSLDs) and Gafchromic film in the occipital region (back side) of a PMMA phantom, were consistent but variations in dose at other locations were significantly higher. The three OSLDs used in this study were found to be suitable for radiation dose measurement in dental units.

Photoluminescent and Thermoluminescent Studies of Dy3+ and Eu3+ Doped Y2O3 Phosphors.

Eu3+ doped and Dy3+ codoped yttrium oxide (Y2O3) phosphors have been prepared using solid-state reaction technique (SSR). The prepared phosphors were characterized by X-ray diffractometer (XRD), energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM) and Fourier transforms infrared spectroscopy (FTIR) techniques. Photoluminescence (PL) and Thermoluminescence (TL) properties were studied in detail. PL emission spectra were recorded for prepared phosphors under excitation wavelength 254 nm, which show a high intense peak at 613 nm for Y2O3:Dy3+, Eu3+ (1:1.5 mol %) phosphor. The correlated color temperature (CCT) and CIE analysis have been performed for the synthesized phosphors. TL glow curves were recorded for Eu3+doped and Dy3+codoped phosphors to study the heating rate effect and dose response. The kinetic parameters were calculated using peak shape method for UV and γ exposures through computerized glow curve deconvolution (CGCD) technique. The phosphors show second order kinetics and activation energies varying from 5.823 × 10- 1 to 18.608 × 10- 1 eV.

Multi-institutional dose audit in radiotherapy facilities using in-house developed optically stimulated luminescence disc dosimeters.

Aim: The aim of this study was to carried out the audit of radiotherapy centers practicing conformal radiotherapy techniques and demonstrate the suitability of this indigenous optically stimulated luminescence (OSL) disc dosimeters in beam quality audit and verification of patient-specific dosimetry in conventional and conformal treatments in radiotherapy. Materials and Methods: Dose audit in conventional and conformal (intensity-modulated radiotherapy and volumetric-modulated arc therapy) radiotherapy techniques was conducted using in-house developed Al2O3:C-based OSL disc dosimeter and commercially available Gafchromic EBT3 film in 6 MV (flat and unflat) photon and 6 and 15 MeV electron beams. OSL disc dosimeter and Gafchromic EBT3 film measured dose values were verified using the ionization chamber measurements. Results: Percentage variations of doses measured by OSL disc dosimeters and EBT3 Gafchromic film for conventional radiotherapy technique were in the range of 0.15%-4.6% and 0.40%-5.45%, respectively, with respect to the treatment planning system calculated dose values. For conformal radiotherapy techniques, the percentage variations of OSL disc and EBT3 film measured doses were in the range of 0.1%-4.9% and 0.3%-5.0%, respectively. Conclusion: The results of this study supported by statistical evidence provided the confidence that indigenously developed Al2O3:C-based OSL disc dosimeters are suitable for dose audit in conventional and advanced radiotherapy techniques.

PATIENT-SPECIFIC DOSIMETRY USING IN-HOUSE DEVELOPED OSL DISC DOSEMETERS.

Circular discs of diameter 5 mm were made from three indigenously developed optically stimulated luminescent (OSL) phosphors for medical dosimetry. Dosimetric characteristics of these discs were evaluated for their use in machine and patient-specific dosimetry in radiotherapy. Uncertainty in dosimetric measurements using these discs was also estimated, and combined standard uncertainty in measurement of absorbed dose was found to be 3.34%. Characterisation studies indicate that OSL discs are suitable for dosimetric application in radiotherapy. These discs were also used for patient-specific dosimetry in conventional and conformal radiotherapy treatments (five different cases) vis-à-vis ionisation chamber and Gafchromic EBT3 film. Doses measured by OSL discs were found comparable to ionisation chamber and Gafchromic EBT3 film measured values and radiotherapy treatment planning system (TPS) calculated dose values in all the cases. The variation between TPS calculated dose values and OSL discs measured dose values was found within the measurement uncertainty.

Effect of rare earth doping on optical and spectroscopic characteristics of BaZrO3:Eu3+,Tb3+ perovskites.

This paper reports structural investigations of rare earth doped BaZrO3 phosphors synthesized by Solid state reaction technique with varying concentrations of Eu3+ and Tb3+ from 0 mol% to 2 mol%. The synthesized phosphors show enhanced variable emissions in the visible region corresponding to different hypersensitive electronic transitions of Eu3+ and Tb3+ ions. With cubic structure confirmed in XRD analysis, the FESEM images show uniform grain connectivity and homogeneity of prepared samples. The TEM micrographs of the synthesized phosphors show agglomerated irregular structures. The synthesized phosphors were also subjected to FTIR, Raman, EDXS analysis along with studies of thermoluminescent and photoluminescent characteristics. On subjecting to 229 nm (UV) excitation, the phosphors show enhanced PL emissions corresponding to 571 nm (5D0-7F0), 591 nm (5D0-7F1), 615 nm (5D0-7F2) and 678 nm (5D0-7F4) hypersensitive transitions of Eu3+ ions and emission peaks at 489 nm (5D4-7F6), 539 nm (5D4-7F5), 589 nm (5D4-7F4) and 632 nm (5D4-7F3) accounting for electronic transitions of Tb3+ ions respectively. The computed average PL lifetime is 14.014 s. In the TL analysis, the second order of kinetics with the activation energy varying from 5.0 × 10-1 eV to 6.6 × 10-1 eV is reported. The maximum TL lifetime is estimated as 19.4985 min in the TL lifetime analysis.