Medical Dosimetry Research Articles

Exploring the viability of desiccant silica gel beads as A novel material for radiation dosimetry: A preliminary investigation

Silica gel bead material, with its porous structure, high surface area, uniform particle size, stability, and excellent adsorption capacity, is a key material for advancing dosimeter technologies. These qualities make it ideal for accurately measuring and monitoring ionizing radiation in various environments. The research aims to characterize the response of different ionizing radiation sources on desiccant silica gel beads, laying the groundwork for potential applications in medical dosimetry. In this study, silica gel bead samples were subjected to various radiation sources, including gamma rays with an average energy of 1.25 MeV, photons (6 MV), and electrons (6 MeV). The radiation was administered at doses within the range of 2 Gy–20 Gy, which is commonly used in radiotherapy to evaluate the dosimetric behaviour of the desiccant silica gel bead samples using the conventional thermoluminescence (TL) technique. The silica gel bead samples have been found to provide a highly linear dose response within the dose range of interest, with the coefficient of determination (R2) ranging between 0.91 and 0.96. Additionally, the samples show high sensitivity at lower doses and maintain excellent reproducibility, with a standard deviation of less than 4%. In regard to fading evaluation, desiccant silica gel beads exhibit minimal signal loss within 35 days post-irradiation, averaging between 20% and 38%. The findings of this study are promising for developing a new dosimeter, which will enhance radiation monitoring and measurement practices in various environments. These improvements cover dosimetric applications in medical and industrial fields including food safety and agricultural development.

LiAlO2:Gd-Based Versatile and Ultrasensitive Detector for Gamma and Neutrons by Thermal and Optical Stimulation.

Considering the low-level dose detection requirement for neutron and γ radiation in cancer therapy, synthesis and exploratory studies have been performed on a newly developed phosphor LiAlO2:Gd. Our results reveal that the presence of both Li and Gd makes it sensitive to both gamma and thermal neutrons. The applicability of LiAlO2:Gd for beta, gamma, and neutrons in both thermally stimulated and optically stimulated modes has been verified by extensive experiments followed by kinetic parametric evaluation with theoretical calculations. The current work confirms that LiAlO2:Gd is a highly sensitive phosphor with a minimum detectable dose of 5.7 μSv for gamma and 92 μSv for themral neutrons. The phosphor is found to show very high sensitivity at low energy and dose. Its ability for detection and discrimination of both gamma and thermal neutrons makes it a potential material to be used in medical dosimetry.

H-BN layered material: A new frontier in radiation dosimetry

This study explores the potential of hexagonal boron nitride (h-BN) nanostructures for dosimetry of diverse ionizing radiation. We focus on the crucial thermoluminescence (TL) properties of h-BN, including glow curve, dose-response, reproducibility, sensitivity, and fading, within the conventional framework of TL dosimetry. The h-BN powder samples were exposed to different ionizing radiations, including 60Co gamma-rays with a mean energy of 1.25 MeV, electrons (6 MeV), and photons (6 MV), at levels of dose familiar in radiotherapy ranging from 2 Gy to 15 Gy. The h-BN's effective atomic number of 6.25, similar to human tissue, opens up exciting possibilities for applications in medical imaging and dosimetry. Notably, h-BN demonstrates a linear response within the dose range of interest, showcasing excellent sensitivity, particularly at low doses and low photon energies. Additionally, h-BN samples exhibit remarkable reproducibility, with a standard deviation of less than 2.4%, albeit accompanied by significant fading. Regarding the trapping parameters underpinning the manifestation of the glow curves of the irradiated samples, use was made of the peak shape method with different models to estimate the order of kinetics (b), activation energy (E), and frequency factor (s) or escape probability and trap lifetime (τ). The data suggest that the TL glow peaks of the h-BN obey general-order kinetics. These findings underscore the transformative potential of h-BN layered material in advancing radiation dosimetry, particularly in medical physics fields. The inherent characteristics of h-BN, coupled with its effective atomic number, excellent linearity over a wide range of radiation doses especially for electron irradiation and better reproducibility, positioned it as a suitable tool for precise and reliable dose measurement in medical imaging and therapy, heralding a new frontier in radiation dosimetry.

Research on water equivalence and angle dependence of medical POF scintillation dosimeters

In radiation dosimetry and medical dosimetry, optical fiber dosimeters have great advantages in application due to their small size and long transmission distance. However, in some low-dose radiation environments, the water inequivalence error and angle error of optical fiber dosimeters can have significant impacts that cannot be ignored. In this paper, the effects of ray energy, ray solid angle and optical fiber probe size on water inequivalence error and angle error are analyzed by using Monte Carlo simulation. Due to the complexity of the influencing factors of the angle error, which is difficult to be analyzed precisely and quantitatively, a correction method based on BP neural network is proposed. The final validation results demonstrate that the correction scheme can reduce the total angle error of the optical fiber dosimeter to 2.72%.

Position-resolved charge collection of silicon carbide detectors with an epitaxially-grown graphene layer

Silicon carbide (SiC) has outstanding physical properties therefore, diodes based on SiC are being considered for many radiation detection applications such as particle accelerator experiments and medical dosimetry. Moreover, by reducing the metal on the surface of the diode there is the potential to enhance its performance in some fields where the presence of metal is detrimental. To this end, SiC detectors with an epitaxially-grown graphene layer (EG), that substitutes the metallic contact, in the sensitive region were produced at IMB-CNM, profiting from the conductivity of the mono-atomic layer material. To isolate the effect of the graphene on the charge collection, samples without graphene were produced in parallel. In this paper, the effect of EG on Silicon Carbide p-in-n radiation detectors is studied in terms of charge collection with a radioactive source and by means of the transient current technique (TCT), which allows for position-dependent signal formation analysis. As a result of the former, we show the capability of the EG-SiC sensor for charge collection after signal integration, to a resolution close to that of a sensor fully metallised. Moreover, from the TCT studies, we observe uniform charge collection across the active region, as well as an up-to ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document}40% transient amplitude damping which, compared with the ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document}90% on the sample containing no metallic contact, proves that the presence of graphene benefits the performance of the device and that the technology is viable for radiation detection as an alternative to metal.

Efficacy and Safety of Radiation Segmentectomy with 90Y Resin Microspheres for Hepatocellular Carcinoma.

Background Limited data are available on radiation segmentectomy (RS) for treatment of hepatocellular carcinoma (HCC) using yttrium 90 (90Y) resin microsphere doses determined by using a single-compartment medical internal radiation dosimetry (MIRD) model. Purpose To evaluate the efficacy and safety of RS treatment of HCC with 90Y resin microspheres using a single-compartment MIRD model and correlate posttreatment dose with outcomes. Materials and Methods This retrospective single-center study included adult patients with HCC who underwent RS with 90Y resin microspheres between July 2014 and December 2022. Posttreatment PET/CT and dosimetry were performed. Adverse events were assessed using the Common Terminology Criteria for Adverse Events, version 5.0. Per-lesion and overall response rates (ie, complete response [CR], objective response, disease control, and duration of response) were assessed at imaging using the Modified Response Evaluation Criteria in Solid Tumors, and overall survival (OS) was assessed using Kaplan-Meier analysis. Results Among 67 patients (median age, 69 years [IQR, 63-78 years]; 54 male patients) with HCC, median tumor absorbed dose was 232 Gy (IQR, 163-405 Gy). At 3 months, per-lesion and overall (per-patient) CR was achieved in 47 (70%) and 41 (61%) of 67 patients, respectively. At 6 months (n = 46), per-lesion rates of objective response and disease control were both 94%, and per-patient rates were both 78%. A total of 88% (95% CI: 79 99) and 72% (95% CI: 58, 90) of patients had a per-lesion and overall duration of response of 1 year or greater. At 1 month, a grade 3 clinical adverse event (abdominal pain) occurred in one of 67 (1.5%) patients. Median posttreatment OS was 26 months (95% CI: 20, not reached). Disease progression at 2 years was lower in the group that received 300 Gy or more than in the group that received less than 300 Gy (17% vs 61%; P = .047), with no local progression in the former group through the end of follow-up. Conclusion Among patients with HCC who underwent RS with 90Y resin microspheres, 88% and 72% achieved a per-lesion and overall duration of response of 1 year or greater, respectively, with one grade 3 adverse event. In patients whose tumors received 300 Gy or more according to posttreatment dosimetry, a disease progression benefit was noted. © RSNA, 2024 Supplemental material is available for this article.

TEAM participation in the irradiation of IROC phantoms for cooperative group clinical trials

The participation of radiation oncology team members in the irradiation of Imaging and Radiation Oncology Core (IROC) phantom for cooperative group clinical trials is essential to comply with the latest quality management philosophy. Medical dosimetrists are expected to develop treatment plans for the irradiation of IROC phantoms. For advanced treatment techniques, such as three-dimensional conformal radiation therapy (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT), the irradiation of the IROC phantoms serves as quality audit. If successful, the irradiation processes demonstrate that the institution has the knowledge of the protocol, and has the appropriate equipment to comply with the protocol requirements. This article describes three IROC phantoms used for credentialing external beam photon beam therapy, delivered using conventional medical linear accelerators, to the medical dosimetry community. Guidance and strategies for the development of treatment plans are discussed. Our institutional irradiation of the three IROC phantoms, delivered using the Truebeam medical linear accelerator, resulted in consistent dose accuracy to within ±1%. The participation of the team members may reduce the overall published failing rate stated to be about one-third of all participating institutions.

Structural Properties of Thermoluminescence Dosimeter Materials, Preparation, Application, and Adaptability: A Systematic Review

Thermoluminescence dosimeters (TLDs) are widely used in radiation dosimetry due to their excellent properties, such as high sensitivity, small size, and ability to measure low doses of radiation. This review focuses on the structural properties of TLD materials, as well as their preparation, application, and adaptability. The review covers the various types of TLD materials, crystal structure, and properties, including energy response and fading characteristics. The different methods used to prepare TLD materials, such as solid-state synthesis, sol-gel synthesis, and solution growth methods, are discussed in detail. The review also includes a detailed discussion of the various applications of TLDs, including medical, environmental, and industrial radiation dosimetry. Extensive information on TLD is reviewed, and the TL characteristics that have a noticeable impact on the TL dosimetry potential for human and other purpose utilisation, such as mineral, oil, and gas resource investigation, can be done using natural and artificial TL signals. Information on TL measurement process requirements and the TL characteristics that have a noticeable impact on a compound TL dosimetry potential are also addressed. Finally, the review concludes by highlighting the adaptability of TLD materials to different dosimetry applications and their potential use in the future.

Investigation of structural, photo and thermoluminescence properties of YAGG:Ce nanogarnet for medical dosimetry application

Cerium-doped yttrium aluminum gallium garnet (YAGG:Ce3+) nanophosphors were synthesized using the sol-gel method. Mixed garnet of Y2.97Al5-xGaxO12:Ce0.03 was prepared with varying gallium content: x = 0, 1, 2 and 3 Ga. The effect of gallium substitutions on the structural, photo and thermoluminescence properties of the prepared nanophosphors were studied by X-ray diffraction (XRD), photoluminescence (PL) and thermoluminescence (TL) techniques. XRD results indicated that the single and pure cubic crystal phase was formed for all nanophosphor samples regardless of the Ga content. The PL spectra of all the samples exhibited a green-yellow emission band centered at 522 nm attributed to the 5d → 4f transitions of Ce3+ ions. The TL glow curve spectra recorded after β-particle irradiation showed a strong dependence in terms of position, shape and intensity, of all temperature peaks with the Ga content. The highest TL sensitivity was observed for the sample prepared with x = 2 Ga, with main peak arising at low temperature (85 °C). The sample prepared at x = 1 Ga exhibited also high TL sensitivity with a simple glow curve spectrum showing a main peak at high temperature (∼158 °C). Thus, the linear dose response of this sample has been investigated in the wide dose range from 0.125 to 100 Gy in order to evaluate the potentiality of this material for radiation dosimetry applications.

First use of silicon carbide detectors with graphene-enhanced contacts for medical dosimetry

Silicon Carbide (SiC) is a radiation hard wide bandgap semiconductor, which makes it an interesting alternative for radiation detector fabrication, with potential applications such as High Energy Physics, synchrotron and radiotherapy instrumentation. In addition, by reducing the amount of metal over the active area of said detectors (typically used for electrical connectivity with the implant of the pn-junction) unwanted effects from secondary interactions which can affect the accuracy of the measurement can be diminished, essential to meet the medical standards of precision. In this article, the use of epitaxially-grown graphene is explored as an alternative to metallic contacts with these prototypes. To this end, the first prototypes of SiC diodes with epitaxial graphene contacts were produced at IMB-CNM for radiation detection,along with reference devices. In order to characterise the feasibility of the technology in the medical application, the dose rate linearity of the SiC device with graphene was measured in a radiotherapy Linac in the dose rate range of 1–6 Gy/min. The response of the device was compared to that observed on devices with similar geometries reported elsewhere. To fully characterise the devices, the same exercise was repeated in a laboratory X-ray tube. Under the later set-up, the prototype is compared against a device with a fully metallised active region.

On the gamma radiation response of commercially available 3D printing materials for medical dosimetry

3D printing technology has rapidly spread for decades, allowing the fabrication of medical implants and human phantoms and revolutionizing healthcare. The objective of this study is to evaluate some radiological properties of commercially available 3D printing materials as potential tissue mimicking materials. Among fifteen materials, we compared their properties with nine human tissues. In all materials and tissues, exposure and energy absorption buildup factors were calculated for photon energies between 0.015 and 15 MeV and penetration depths up to 40 mean free path. Furthermore, the Geant4 Monte Carlo toolkit (version 10.5) was used to simulate their percentage depth dose distributions. In addition, equivalent atomic numbers, effective atomic numbers, attenuation coefficients, and CT numbers have been examined. All parameters were considered in calculating the average relative error (σ), which was used as a statistical comparison tool. With σ between 6 and 7, we found that Polylactic Acid (PLA) was capable of simulating eye lenses, blood, soft tissue, lung, muscle, and brain tissues. Moreover, Polymethacrylic Acid (PMAA) material has a σ value of 4 when modeling adipose and breast tissues, respectively. Aside from that, variations in 3D printing materials’ infilling percentage can affect their CT numbers. We therefore suggest the PLA for mimicking soft tissue, muscle, brain, eye lens, lung and blood tissues, with an infill of between 92.7 and 94.3 percent. We also suggest an 89 percent infill when simulating breast tissue. Furthermore, with a 96.7 percent infill, the PMAA faithfully replicates adipose tissue. Additionally, we found that a 59 percent infill of Fe-PLA material is comparable to cortical bone. Due to the benefits of creating individualized medical phantoms and equipment, the results might be seen as an added value for both patients and clinicians.

Exploring the role of combined external beam radiotherapy and targeted radioligand therapy with [177Lu]Lu-PSMA-617 for prostate cancer - from bench to bedside.

Management of prostate cancer (PC) might be improved by combining external beam radiotherapy (EBRT) and prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) with lutetium-177 (177Lu)-labeled PSMA inhibitors. We hypothesized a higher efficacy of the combination due to augmentation of the radiation dose to the tumor and interactions of EBRT with PSMA expression potentially increasing radiopharmaceutical uptake. Therefore, this study analyzed the influence of radiation on PSMA expression levels in vitro. The results were translated to evaluate the efficacy of the combination of photon EBRT and [177Lu]Lu-PSMA-617 in a murine PC xenograft model. Finally, a clinical case report on a combined elective field EBRT with RLT dose escalation illustrates a proof-of-concept. Methods: PSMA gene and protein expression were assessed in human PSMA-overexpressing LNCaP cells after irradiation using reverse transcription quantitative polymerase chain reaction (RT-qPCR), flow cytometry and On-Cell Western assays. In the in vivo therapy study, LNCaP tumor-bearing BALB/c nu/nu mice were irradiated once with 2 Gy X-ray EBRT and injected with 40 MBq [177Lu]Lu-PSMA-617 after 4 h or received single or no treatment (n = 10 each). Tumor-absorbed doses by [177Lu]Lu-PSMA-617 were calculated according to the Medical Internal Radiation Dosimetry (MIRD) formalism after deriving time-activity curves using a gamma probe. An exemplified patient case is demonstrated where fractionated EBRT (54 Gy to prostate; 45 Gy to pelvic lymphatics) and three cycles of [177Lu]Lu-PSMA-617 (3.4-6.0 GBq per cycle) were sequentially combined under concurrent androgen deprivation for treating locally advanced PC. Results: At 4 h following irradiation with 2-8 Gy, LNCaP cells displayed a PSMA protein upregulation by around 18% relative to non-irradiated cells, and a stronger upregulation on mRNA level (up to 2.6-fold). This effect was reversed by 24 h when PSMA protein levels were downregulated by up to 22%. Mice treated with the combination therapy showed significantly improved outcomes regarding tumor control and median survival (p < 0.0001) as compared to single or no treatment. Relative to monotherapy with PSMA-RLT or EBRT, the tumor doubling time was prolonged 1.7- or 2.7-fold and the median survival was extended by 24% or 60% with the combination, respectively. Additionally, tumors treated with EBRT exhibited a 14% higher uptake of the radiopharmaceutical as evident from the calculated tumor-absorbed dose, albeit with high variability in the data. Concerning the patient case, the tri-modality treatment was well tolerated and the patient responded with a long-lasting complete biochemical remission for five years following end of PSMA-RLT. The patient then developed a biochemical relapse with oligo-recurrent disease on follow-up imaging. Conclusion: The present preclinical and clinical data demonstrate that the combination of EBRT with dose escalation by PSMA-RLT improves tumor control and potentially prolongs survival. This may pave the way for further clinical investigations of this approach to explore the curative potential of the combination therapy.

Monte Carlo investigation of S-values for 111In radionuclide therapy

Novel therapeutic strategy in radionuclide therapy use cell-penetrating monoclonal antibodies to carry Auger-emitting radionuclides into the cells. Estimation of dose in normal and tumor cells are important to investigate the efficacy and toxicity of treatment. Monte Carlo simulation is the most suitable method for estimation of absorbed dose at microscopic level. It is therefore useful to carry out Monte Carlo simulation of Auger emitting radionuclides in order to assess the sensitivity of the results with respect to transport approximations generally used in Monte Carlo codes. There are several Auger emitting radionuclides with potential clinical applications, however, based on their half-life 111In is the most suitable for Auger therapeutic purposes and was considered in the present investigation. Geant4 Monte Carlo simulation was performed and specific absorbed dose fraction (or S-values) for 111In were calculated by using different physics model (Standard, Livermore, Penelope and Geant4-DNA) and compared with Medical Internal Radiation Dosimetry (MIRD) S-values. Source was distributed in the cytoplasm (Cy), surface (Cs) and nucleus (N). Average of relative differences (RD) (%) were calculated for self and cross absorbed dose. RD(%) for self-absorption (NßN) were 4.4, 2.36, 6.21 and 1.1 for Standard, Penelope, Livermore and Geant4-DNA respectively. For cross-absorption these values were higher (e.g. for NßCy 15.4, 18.36, 19.21 and 24.8 for Standard, Penelope, Livermore and Geant4-DNA respectively). Cutoff energy considered for electrons and gamma photons affect the results in dose estimation for Auger electrons in Monte Carlo simulation.

Magnetic field influence on the light yield from fiber-coupled BCF-60 plastic scintillators of relevance for output factor dosimetry in MR-linacs

Organic plastic scintillators are of interest for ionizing radiation dosimetry in megavoltage photon beams because plastic scintillators have a mass density very similar to that of water. This leads to insignificant perturbation of the electron fluence at the point of measurement in a water phantom. This feature is a benefit for dosimetry in strong magnetic fields (e.g., 1.5 T) as found in linacs with magnetic resonance imaging. The objective of this work was to quantify if the light yield per dose for the scintillating fiber BCF-60 material from Saint-Gobain Ceramics and Plastics Inc. is constant regardless of the magnetic flux density. This question is of importance for establishing traceable measurement in MR linacs using this detector type. Experiments were carried out using an accelerator combined with an electromagnet (max 0.7 T). Scintillator probes were read out using chromatic stem-removal techniques based on two optical channels or full spectral information. Reference dosimetry was carried out with PTW31010 and PTW31021 ionization chambers. TOPAS/GEANT4 was used for modelling. The light yield per dose for the BCF-60 was found to be strongly influenced by the magnitude of the magnetic field from about 1 mT to 0.7 T. The light yield per dose increased (1.3 ± 0.2)% (k = 1) from 1 mT to 10 mT and it increased (4.5 ± 0.9)% (k = 1) from 0 T to 0.7 T. Previous studies of the influence of magnetic fields on medical scintillator dosimetry have been unable to clearly identify if observed changes in scintillator response with magnetic field strength were related to changes in dose, stem signal removal, or scintillator light yield. In the current study of BCF-60, we see a clear change in light yield with magnetic field, and none of the other effects.

The role of standards laboratories in reducing uncertainty in clinical dosimetry: A Canadian perspective

As a National Metrology Institute, the National Research Council Canada (NRC) provides confidence in measurement results, and data traceable to SI units. This paper outlines some of the ways that the NRC contributes to reducing measurement uncertainty in clinical medical physics dosimetry. These activities include, (i) the improvement of existing primary standards and traceability for established beam modalities, such as MV photon and electron beams; (ii) improving measurement accuracy for new beam modalities through the development of transportable systems which permit operation at the user’s facility; (iii) contributing to new dosimetry protocols, best practice reports and educational outreach; and (iv) supporting the verification of clinical implementation by offering dosimetry auditing capabilities through coordination with the clinical medical physics community.

Testing the [formula omitted] procedure using TLDs and OSLDs and a lexsyg smart automated reader for precise dosimetry

This work demonstrates the precision achieved with thermoluminescence (TL) and optically stimulated luminescence (OSL) detectors (TLDs and OSLDs) using a procedure that takes advantage of the capabilities of automated TL/OSL readers (lexsyg smart), for potential applications in medical dosimetry. The procedure makes use of the 90Sr/90Y beta source present in the reader to correct for sample-to-sample sensitivity variations. Typical data obtained using four types of TLDs (LiF:Mg,Ti, LiF:Mg,Cu,P, CaF2:Tm, Al2O3:C single crystal) and two types of OSLDs (BeO and Al2O3:C film) are presented along with the estimated uncertainties achieved. The results demonstrate that the material-specific optimized procedure enables a precision (standard deviation of the data) better than 3% in the 0.2Gy–2Gy dose range with all the materials, except for the TL signal of Al2O3:C single crystal. The highest precision (¡ 1%) is achieved using the OSL from Al2O3:C film over a wide dose range (∼0.2Gy to 10Gy).

Occupational radiation exposure in anesthesia for hepatic chemoembolization: a prospective study

Introduction: Anesthetists play an important role during interventional radiology procedures. Like the main operator, anesthetists may also be subject to significant radiation levels in the fluoroscopy suite. Due to its complexity, hepatic chemoembolization procedures demand high fluoroscopic times and digital subtraction angiography images, exposing patients and medical staff to high radiation doses.&#x0D; Objetive: To assess and quantify the radiation to which one anesthetist was exposed over the course of seven consecutive hepatic chemoembolization procedures, and compare it to the exposure received by the main operator.&#x0D; Methods: Medical staff dosimetry was evaluated during seven consecutive hepatic chemoembolization procedures conducted in a private hospital in Recife (Brazil), using thermoluminiscent dosimeters placed in regions of the head and torso.&#x0D; Results: For the seven procedures evaluated in this study, the anesthetist received, on average, absorbed doses to the glabella, left eyebrow, right eyebrow and effective dose of 142.4 ± 72 µSv, 117.3 ± 66 µSv, 137.8 ± 71 µSv and 12.4 ± 8.4 µSv, respectively. &#x0D; Conclusions: In some cases, ocular dose and effective dose received by the anesthetist may be 4 and 4.7 times greater, respectively, when compared to the main operator. According to the results of this study, the current occupational annual dose limit to the lens of the eye of 20 mSv can be exceeded with only two hepatic chemoembolization procedures per week if adequate radiation protection conditions are not guaranteed.

Defect Induced MgO: Li, Sm nanophosphor as a new highly sensitive material for thermoluminescence dosimetry

MgO is drawing considerable attention owing mainly due to its tissue equivalency (Zeff = 10.8) and excellent luminescence response. In this work, we report the synthesis and investigation of a highly sensitive MgO: Li, Sm phosphor in nanocrystalline form for TL dosimetry application. The structural and morphological study has been done using X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). TL intensity of gamma irradiated MgO nanophosphor increases with doping of Li and further improves by co-doping with Sm. The MgO: Li, Sm nanophosphor exhibit TL glow curve structure having isolated single peak at 169 °C and linearity in the low dose (13 mGy-5 Gy) as well as high dose range (10–1000 Gy). The TL structure and peak position remains stable at all doses. The phosphor shows excellent stability (low fading rate) and repeatability. TL intensity of MgO: Li, Sm is 12 times higher than that of commercially available LiF: Mg, Ti (TLD 100) and almost equivalent to LiF: Mg, Cu, P (TLD-700 H). This may be attributed to the formation of greater number of density of traps and suitable trapping levels with optimum dopant selection in MgO nanophosphor. The incorporation of the Sm3+ has improved the TL intensity manifold with appearance of desired isolated single peak. The photoluminescence (PL) spectra confirm the Sm3+ emission at 566, 603, 651 and 708 nm with an excitation wavelength of 315 nm. Further the role of dopants has been discussed on the basis of charge transfer mechanism and corelated with associated kinetic parameters for better understanding of TL process. The newly explored MgO: Li, Sm nanophosphor has shown attractive TL dosimetry properties owing to its high sensitivity, stable glow curve structure, dose linearity, low fading and repeatability which meet all the requirement to establish this as a next generation TL phosphor for medical and personal dosimetry application.

Carbon rich media for luminescence-based surface dosimetry and study of associated surface defects

The present study continues research into the utilisation of carbonaceous media for medical radiation dosimetry, focusing on the effects of surface area-to-volume ratio and carbon content on structural interaction alterations and dosimetric properties in sheet- and bead-type graphitic materials (with the respective carbon content of ∼98 wt% and ∼90 wt%). Using 60Co gamma-rays and doses from 0.5 Gy to 20 Gy, the study has been made of the response of commercially available graphite in the form of 0.1 mm, 0.2 mm, 0.3 mm and 0.5 mm thick sheets, also of activated carbon beads. Confocal Raman and photoluminescence spectroscopy have been employed, examining radiation-induced structural interaction alterations. Dose-dependent variation in the Raman intensity ratio ID/IG relates to the varying dominance of defect generation and dose-driven defect annealing. Of the various thickness graphite sheets, the 0.1 mm thick medium possesses the greatest surface area-to-volume ratio. Perhaps unsurprisingly, it also exhibits the greatest thermoluminescence (TL) yield compared to that of the other carbonaceous sheet foils used herein. Moreover, the second greatest mass-normalised TL yield has been observed to be that of the porous beads, reflected in the greater defect density (ID/IG > 2) when compared to the other media, due in part to their inherent feature of large internal surface area. Considering the challenge posed in matching skin thickness with skin dose, the near tissue equivalent graphite sheets show particular promise as a skin dosimeter, sensitive as a function of depth.

Prompt gamma ray activation analysis for determining chemical composition of 3D printing and casting materials used in biomedical applications.

Three-dimensional printing and casting materials were analyzed by prompt gamma-ray activation analysis (PGAA) to determine their suitability as human tissue surrogates for the fabrication of phantoms for medical imaging and radiation dosimetry applications. Measured elemental compositions and densities of five surrogate materials simulating soft tissue and bone were used to determine radiological properties (x-ray mass attenuation coefficient and electron stopping power). When compared with radiological properties of International Commission on Radiation Units and Measurements (ICRU) materials, it was determined that urethane rubber and PLA plastic yielded the best match for soft tissue, while silicone rubber and urethane resin best simulated the properties of bone.