Radiophotoluminescence Research Articles

OUT-OF-FIELD DOSES IN CHILDREN TREATED FOR LARGE ARTERIOVENOUS MALFORMATIONS USING HYPOFRACTIONATED GAMMA KNIFE RADIOSURGERY AND INTENSITY-MODULATED RADIATION THERAPY.

The purpose of this study was to measure out-of-field organ doses in two anthropomorphic child phantoms for the treatment of large brain arteriovenous malformations (AVMs) using hypofractionated gamma knife (GK) radiosurgery and to compare these with an alternative treatment using intensity-modulated radiation therapy (IMRT). Target volume was identical in size and shape in all cases. Radiophotoluminescent (RPL), thermoluminescent (TL) and optically stimulated luminescent (OSL) dosimeters were used for out-of-field dosimetry during GK treatment and a good agreement within 1-2% between results was shown. In addition, the use of multiple dosimetry systems strengthens the reliability of the findings. The number of GK isocentres was confirmed to be important for the magnitude of out-of-field doses. Measured GK doses for the same distance from the target, when expressed per target dose and isocentre, were comparable in both phantoms. GK out-of-field doses averaged for both phantoms were evaluated to be 120 mGy/Gy for eyes then sharply reduced to 20 mGy/Gy for mandible and slowly reduced up to 0.8 mGy/Gy for testes. Taking into account the fractionation regimen used to treat AVM patients, the total treatment organ doses to the out-of-field organs were calculated and compared with IMRT. The eyes were better spared with GK whilst for more distant organs doses were up to a factor of 2.8 and 4 times larger for GK compared to IMRT in 5-year and 10-year old phantoms, respectively. Presented out-of-field dose values are specific for the investigated AVM case, phantoms and treatment plans used for GK and IMRT, but provide useful information about out-of-field dose levels and emphasise their importance.

Eu-doped Ca2SiO4 as a New Radio-photoluminescence Phosphor

Eu-doped Ca2SiO4 ceramics have been newly found to show radio-photoluminescence (RPL). An as-prepared material shows photoluminescence (PL) only due to Eu3+ whereas an additional broad emission due to Eu2+ appears in the red region as a result of RPL after X-ray irradiation. The RPL is attributed to the intravalence conversion of the Eu ion (Eu3+ → Eu2+), and this response can be detected as low as 10 mGy of X-ray dose.

Radiophotoluminescence and thermoluminescence characteristics of undoped and Mg doped LiF phosphor in the high dose region

Radiophotoluminescence (RPL) and thermoluminescence (TL) from undoped and Mg-doped LiF powder samples were investigated for high dose dosimetric applications. F-aggregate centres in LiF are created by radiolysis. The RPL emission at 530 nm and 650 nm from F3+ and F2 centres respectively (on excitation at 450 nm) in undoped commercial LiF powder enhanced with increasing sintering temperature. Its TL glow curve showed peaks at 145, 290 and 365 °C. The RPL-TL correlation studies carried out for the first time showed that the thermal annihilation of F3+ and F2 centes following Fi0 - Va (interstitial-vacancy) recombination cause 290 °C and 365° TL peaks respectively. This showed that F2 centres are thermally more stable than F3+ centres. Its integrated TL response kept increasing nearly linearly up to 14 kGy, in contrast to the response of the TL peaks in dosimetry grade LiF:Mg, Ti (TLD-100). However, the TL from LiF suffers from fading problems. A 100 °C, 15 min pre-read annealing treatment erased most of the 145 °C TL peak without disturbing the other high temperature peaks. A 750° C, 22 h sintering treatment in carbon atmosphere shifted the major TL glow peak of undoped LiF to 200 °C but reduced its TL sensitivity by more than a factor of 10. Mg-doped LiF samples exhibit a TL glow curve peaking at ∼240 °C with satellite peaks typical of Mg doped LiF whose shape did not change significantly with gamma dose. However it showed lower TL and RPL sensitivities as compared to those of undoped LiF. All LiF except LiF alfa (750 °C, 1 h, CB) showed sublinear increase in TL with dose and therefore will cause inaccuracy in dose measurements especially at high doses due to reduced sensitivity. LiF alfa 750 °C, 22 h and 1000 °C, 6 min sintered powder samples are better than others because their RPL sensitivity increases nearly linearly with dose. However, a low fading observed in the latter sample supports its application. The bright yellow RPL emission seen through a 550 nm cut on filter illuminated with a 450 nm blue LED or He-Cd laser light could quickly confirm an irradiated consignment on which LiF samples are affixed. The increase in green to red emission ratio with dose and post-irradiation storage period might be related to slow migration of anion vacancies created by one secondary electron track to F centres created by another track and consequent conversion of F2 → F3+ centres.

Two-photon excited microscale colour centre patterns in Ag-activated phosphate glass written using a focused proton beam

We report a demonstration of microscale patterns in Ag-activated phosphate glass fabricated using a focused proton beam with an energy range of 1–3 MeV. Various microscale patterns are based on blue and orange radiophotoluminescent (RPL) centres. Two- and three-dimensional (2D and 3D) microstructures are visualised by combining two-photon confocal microscopy with femtosecond (fs) laser pulses generated from a mode-locked Ti:sapphire laser operating at 700 nm. The reconstructed images are analytically evaluated using lateral/axial dose mapping and RPL spectra. In addition, the advantages of two-photon excitation applied to Ag-activated phosphate glass are discussed, and this method is compared with single-photon excitation.

Fast skin dose estimation system for interventional radiology.

To minimise the radiation dermatitis related to interventional radiology (IR), rapid and accurate dose estimation has been sought for all procedures. We propose a technique for estimating the patient skin dose rapidly and accurately using Monte Carlo (MC) simulation with a graphical processing unit (GPU, GTX 1080; Nvidia Corp.). The skin dose distribution is simulated based on an individual patient’s computed tomography (CT) dataset for fluoroscopic conditions after the CT dataset has been segmented into air, water and bone based on pixel values. The skin is assumed to be one layer at the outer surface of the body. Fluoroscopic conditions are obtained from a log file of a fluoroscopic examination. Estimating the absorbed skin dose distribution requires calibration of the dose simulated by our system. For this purpose, a linear function was used to approximate the relation between the simulated dose and the measured dose using radiophotoluminescence (RPL) glass dosimeters in a water-equivalent phantom. Differences of maximum skin dose between our system and the Particle and Heavy Ion Transport code System (PHITS) were as high as 6.1%. The relative statistical error (2 σ) for the simulated dose obtained using our system was ≤3.5%. Using a GPU, the simulation on the chest CT dataset aiming at the heart was within 3.49 s on average: the GPU is 122 times faster than a CPU (Core i7–7700K; Intel Corp.). Our system (using the GPU, the log file, and the CT dataset) estimated the skin dose more rapidly and more accurately than conventional methods.

Radio-photoluminescence in non-doped K2CO3 ceramics

In this letter, we report a discovery of a new radio-photoluminescence (RPL) material. The RPL appeared in vacuum-sintered non-doped K2CO3 ceramics as an evolution of PL emission band peaking at 440nm. The RPL signal was confirmed to be sensitive to X-rays and stable at room temperature. The RPL response was observed as low as 1mGy although the sample was not optimized. We strongly believe that this material should be a promising candidate as RPL dosimeter materials.

Non-doped Na2CO3 Ceramics as a New Radio-photoluminescence (RPL) Material

In this letter, we report a new radio-photoluminescence (RPL) material. RPL is a phenomenon that new luminescent centers are generated by ionizing radiations. Sintered Na2CO3 ceramics in a vacuum s...

Background variation and radiation-induced darkening of radiophotoluminescent detectors

Radiophotoluminescent (RPL) detectors are used extensively for measurement of γ, X and β radiations. While these detectors show excellent dosimetric properties, we point out behaviors observed in their routine use that can affect the accuracy of their results. There is a radiation-induced darkening of the detector and a background noise limit beyond which the impact of ionizing radiation on the measurement becomes unclear. Tests show that after several measurement-anneal cycles, the RPL detectors reach a threshold value of intrinsic background, which causes measurements of small doses to be unreliable.

Dynamics of radio-photoluminescence and thermally-stimulated luminescence in KBr:Sm

Sm-doped KBr single crystals were prepared by the Bridgman–Stockbarger technique. The samples show both radio-photoluminescence (RPL) and thermally-stimulated luminescence (TSL). The RPL is due to the valence change of the Sm ion (Sm3+ → Sm2+), induced by X-rays, so the photoluminescence emission by Sm2+ appears as a result of irradiation and the intensity increases with the irradiation dose. The emission of Sm2+ is due to the 5d–4f transitions. The RPL response seems to be related with the thermally-stimulated luminescence (TSL) on the same samples. The TSL emission is predominantly due to Sm2+, instead of Sm3+, indicating that capture of a hole by Sm2+ takes place. As a result of TSL (or heat treatment), Sm2+ reverts to Sm3+ as the original state. The thermal activation energies have been derived from TSL isothermal analyses, and the obtained values are 1.42, 1.55, 1.65, and 1.74 eV.

A comparative evaluation of luminescence detectors: RPL-GD-301, TLD-100 and OSL-AL2O3:C, using Monte Carlo simulations

The luminescent dosimeters are widely used in clinical practice, for the monitoring of patient dose in external radiation therapy. Three of the most common dosimeter categories are the thermoluminescence (TLDs), the radiophotoluminescence (RPLs) and the optically stimulated luminescence (OSLs), with similar physical processes on their properties. The aim of the present study is to compare and evaluate the dosimetric properties of three specific luminescent detectors namely: a) RPL glass dosimeter, commercially known as GD-301, b) lithium fluoride TLD-100 (LiF:Mg,Ti) and c) carbon-doped aluminum oxide (Al2O3:C). For this purpose, Monte Carlo simulations were applied, using the MCNP5 code to estimate the responses of these dosimeters in terms of absorbed dose, output factor, the angular and energy dependence. In the present study, we found that the differences between the output factors were less than ± 4.2% for all detector materials RPLGD, TLD and OSLD. The variations in sensitivity for angles up to ± 80 degrees from the central axis of the beam were approximately 0.5%, 0.8% and 1.5% for the TLD-100, GD-301 and Al2O3:C, respectively. The energy dependence of the RPL and OSL dosimeters are stated as less than a 2.2%, and within 5.8% for TLD.

Where is the best position to place a dosemeter in order to assess the eye lens dose when lead glasses are used?

The objective of this study was to evaluate the feasibility of assessing the eye lens dose when lead glasses are used, by attaching a small radiophotoluminescent (RPL) glass dosemeter to the lead glasses. RPL dosemeters were placed over and under the shielding of the glasses and their response was evaluated for a range of parameters, including irradiations in a standard X-ray beam and Monte Carlo simulations of a cardiac/radiologic intervention (scattered beam). For the specific situations taken into account in this study, the optimal position was found to be a dosemeter placed close to the bridge of the lead glasses, over its shielding.

Micro-PIXE analysis and imaging of radio-photoluminescence glass bead microdosimeters

Sub-millimeter-sized radio photoluminescence (RPL) glass bead microdosimeters using Ag and Cu activators were developed for micrometer-scale dose measurement in particle therapy. To obtain the desired size of RPL glass beads, the RPL glasses containing Ag or Cu activators were heated with carbon microparticles. The elemental composition of RPL glass beads with diameters of 400μm were evaluated by particle-induced X-ray emission analysis using proton microbeam probe with different energy of 1.7 and 3MeV. A nearly uniform elemental distribution was observed in both the Ag and Cu dosimeters indicating the uniform distribution of activator ions, which create the luminescence centers. These results indicate that the sub-millimeter-sized RPL glass bead dosimeters possess the basic properties required for particle dosimetry.

Paediatric organ doses from CT-simulation in brain tumour GK radiosurgery treatment – Phantom study

For the preparation of Gamma Knife (GK) treatments of brain tumours, a head CT examination is necessary when using a new CT-based convolution dose calculation algorithm included in Leksell Gamma Plan software (version 10.1.1). The purpose of this study was to measure the organ doses in paediatric anthropomorphic phantoms during a head CT scan and compare them with the measured GK treatment doses. CT doses were measured with radiophotoluminescence (RPL) dosimeters and compared with results of MC simulations. Measured doses for organs within the CT scan volume were comparable for both phantoms. The highest organ CT dose was evaluated for eyes: 27.6 ± 0.2 mGy and 27.3 ± 0.6 mGy for 5 and 10 year old phantom respectively. Doses for organs not included in the scan volume decreased with distance from the scan volume and were on average 3.5 times higher for the 5 year old phantom compared with the 10 year old phantom. Comparison of measured and MC dose values showed good agreement. For the 10 year old phantom, CT doses were 22%, 6%, 5% and 3% of the GK dose for thyroid, lungs, eyes and breasts respectively. Enhancement of the total organ doses for the whole GK treatment due to CT scanning is not negligible but nevertheless, the use of the new convolution algorithm seems reasonable.

Scintillation, TSL and RPL properties of MgF2 transparent ceramic and single crystal

We have prepared MgF2 transparent ceramics by spark plasma sintering (SPS) and investigated the scintillation and dosimeter properties compared with those of a single crystal. Under X-ray irradiation, a transparent ceramic showed scintillation with a broad feature over 300–600nm with decay times of 310 and 1940μs while the single crystal did not show such emission. It was found that MgF2 show radio-photoluminescence (RPL), which is a generation of new luminescence center by ionizing radiation. The RPL was only observed in the transparent ceramic samples, which appeared as two emission bands peaking around 415 and 700nm under 340±40nm excitation. During the PL reading, the emission band at 415nm effectively increased over 50s. This result suggested that the RPL in MgF2 shows a build-up phenomenon. From PL emission/excitation characteristics and decay time, it was suggested that the RPL peak around 415nm was due to M(C2h) center.

Fluorescent nuclear track images of Ag-activated phosphate glass irradiated with photons and heavy charged particles

In this paper we report about the demonstration of the nuclear track imaging capabilities of Ag-activated phosphate glass. A 375nm laser and confocal laser scanning microscopy (CLSM) were respectively used for track excitation and detection. Specifically, the blue and orange radiophotoluminescent (RPL) tracks and dose distributions observed after irradiation with soft X-rays, gamma rays and heavy charged particles (HCPs) are examined. In addition, the origins of the reductions in RPL efficiency for high-dose X-ray irradiation and for irradiation with HCPs with high linear energy transfer (LET) values are investigated via a CLSM and a conventional fluorescent reader and discussed.

Radiophotoluminescence and optically stimulated luminescence from Al2O3:C,Mg films using a 1D modular reader

The radiophotoluminescence (RPL) and optically stimulated luminescence (OSL) combined signals from Al2O3:C,Mg films were investigated in the dose range of interest in radiotherapy medical dosimetry (0.1–40 Gy). The results showed that the RPL signal is linear over the dose range investigated. The systems based on red excitation have a better dose detection range (starting from 0.2Gy), compared to the system based on UV excitation (1 Gy). The RPL dose measurements are performed using a modular system by illumination of the Al2O3:CMg detectors with 335 nm or 650 nm light and measuring the intensity of the 750 nm fluorescence, while OSL is measured using the modular system with blue 470 nm light. We demonstrated the feasibility of combining RPL and OSL readouts by proposing a protocol where one can acquire cumulative dose response (RPL) and dose reproducibility (OSL). The main challenge was to account for sensitization caused by accumulated dose when using the OSL technique, without affecting the RPL readouts.

Radio-photoluminescence observed in non-doped Mg2SiO4 single crystal

The aim of this research is to investigate radiation-induced luminescence of non-doped Mg2SiO4 single crystal. The Mg2SiO4 single crystals were synthesized by the Czochralski process. The obtained crystal samples were studied to characterize the radio-photoluminescence (RPL), radio-luminescence (RL), and thermally-stimulated luminescence (TSL) properties. A non-irradiated (or as-prepared) sample shows no particular PL features whereas X-ray treated sample shows a broad PL emission around 630 nm under excitation at 270 nm. The latter observation indicates that RPL centre has been generated by X-ray irradiation. The X-ray induced RL can be observed due to the RPL centre around 630 nm, and the intensity monotonically increases with accumulating the incident radiation dose. TSL glow curve consists of three peaks at 160, 260, and 390 °C, and the initial rise method derived the activation energies of 1.33, 1.47, and 1.85 eV, respectively. The first two TSL are associated with some shallow trapping centres, and annealing at this temperature range builds up the RPL response. On the other hand, annealing at higher temperatures supresses the RPL response; thus, the RPL centre is located at deeper site.

Radio-photoluminescence in Sm-doped BaF2-Al2O3-B2O3 glass-ceramics

In this research we have found that Sm-doped BaF2-Al2O3-B2O3 glass ceramics show radio-photoluminescence (RPL) properties associated with X-ray irradiation. Before X-ray irradiation, the photoluminescence (PL) emission is only due to the 4f-4f transitions of Sm3+ observed around 600 nm; however, after X-ray irradiation it shows additional PL emissions due to the 4f-4f transitions of Sm2+. We attributed the origin of this RPL due to the inter-valence conversion of Sm ion (Sm3+ → Sm2+). The glass ceramic sample includes BaAlBO3F2 crystallites in the glass matrix, and the RPL is only valid for Sm included in the crystalline phase since the precursor glass (without the crystalline phase) does not show RPL. The RPL response is so stable that it does not show any indication of fading even by heating at high temperatures up to 400 °C. For radiation sensing applications, we have confirmed that it shows a monotonically increasing response with X-ray dose at least over the 10–10,000 mGy; and it has been demonstrated for 2D dosimetry applications.

Radiophotoluminescence properties of Ag-doped phosphate glasses

The radiophotoluminescence (RPL) of Ag-doped phosphate glass has been used for personal dosimetry for a long time. In this study, we investigated the optical properties of Ag-doped various phosphate glasses. It is revealed that alkali metals in the phosphate are required to achieve the RPL, and that the alkali metals content has an influence on the RPL properties. Also, the ESR signal corresponding to the valence change of Ag was observed only for the phosphate glasses containing alkali metals. These results indicate that the RPL occurs based on the change in Ag valence state, which is consistent with commercial phosphate glasses used for dosimetry. In addition, the decay-time constants of the RPL were on the order of microseconds. Furthermore, initialization of the RPL was observed after heating at 473 K, which indicates that these glasses can be used repeatedly.

Radiation Dose Response of Ag-Doped Phosphate Glasses with Different Alkali Metal Compositions in the Host

Introduction For many years, the radiophotoluminescence (RPL) of Ag-doped phosphate glass has been exploited in personal dosimeters. On exposure to X-ray, gamma ray, and high-intensity laser irradiations, the electrons and holes are captured by the Ag+ ions in the glass structure, thereby changing the Ag+ ions into Ag0 and Ag2+, respectively [1]. Thus, Ag-doped phosphate glasses enable the estimation of the exposure dose due to the correlation between the amount of irradiation and the relative intensity of luminescence of the Ag0 and Ag2+ ions excited with ultraviolet light. In a previous research, we found that the peak wavelengths of the RPL bands depend on the alkali metal species used [2]. In this study, we investigated the radiation dose response of various Ag-doped phosphate glasses, containing alkali metals as cations, to optimize their composition and develop a higher-performance dosimeter. Experimental Methods The glass samples were prepared according to a conventional melt-quenching method in air. The raw materials, AgCl and (LiPO3)n (Li/Ag), were mixed, loaded into an alumina crucible and melted at 1073 K, for 30 min, in an electric furnace. The melt was then quenched on a stainless steel plate at 573 K, which is below the glass transition temperature. The same operations were also performed for NaPO3 (Na/Ag), (KPO3)n (K/Ag)，RbH2PO4 (Rb/Ag)and CsH2PO4 (Cs/Ag) instead of LiPO3. The Ag concentration was 0.1 mol% for all samples. In addition, phosphate glasses with mixed alkali metals were prepared in the same manner Li/Na-Ag, K/Na-Ag, Rb/Na-Ag, and Cs/Na-Ag. The samples were irradiated at room temperature with X-rays using an X-ray tube operating at 40 mA and 40 kV. The PL (photoluminescence) and RPL properties were analyzed using both PL and RPL spectra and the temporal luminescence profiles. The PL and RPL spectra were collected using an F-7000 (Hitachi) fluorescence spectrometer. The temporal profiles were recorded using a DeltaFlex 3000U-TMK2 (Horiba). The absorption spectra were measured using a spectrophotometer (Hitachi U-3500). Results The RPL spectra of the various Ag- doped phosphate glasses, irradiated with a dose of 50-Gy X-rays, are shown in Fig. 1. The sample K/ Na-Ag shows two emission band peaks, observed at 550 nm and 680 nm, with excitation at 310 nm. The peak of K is also detected at 550 nm with a line shapesimilar to that of the sample K/Ag. On the other hand, the peak of K/ Na-Ag observed at 680 nm shows a line shape similar to that of Na/Ag . These results indicate that Na-K/Ag is composed of K/Ag and Na/Ag domains and that Na and K phosphate layers are separately formed around fluorescent centers.