IR Source Research Articles

Trials of transmission imaging using clinically used Ir-192 source for high-dose-rate brachytherapy

In high-dose-rate (HDR) brachytherapy, verification of an Ir-192 source's position during treatment is required. One of the methods for this used a high-energy pinhole gamma camera to image the position of the source, but the absolute position of the source cannot be measured. To confirm the absolute position, it will be useful to acquire the transmission image of a subject in addition to the gamma photon image at the same time without using an additional X-ray system. To measure the transmission images, we tried to use the high-energy gamma photons emitted from the Ir-192 source used for the therapy. We developed a high-energy gamma photon imaging system composed of 1-mm-thick Pr doped Gd2O2S (GOS), a surface mirror, and a cooled charge-coupled device (CCD) camera. The developed imaging system achieved transmission imaging of high-energy gamma photons by transporting the Ir-192 source in front of the imaging system. The spatial resolution of the imaging system was better than 2.4 mm FWHM with and without a 10-cm-thick acrylic block set between the imaging system and the source. Moderate spatial resolution and contrast images of phantoms were obtained with the system. For the dynamic imaging mode, continuous images of the phantoms were measured with 1-sec intervals. There was no observable difference in the transmission images by the movement of the Ir-192 source. Transmission imaging of subjects using an Ir-192 source for HDR brachytherapy could be achieved using our developed imaging system. The system offers a new method to measure the real-time transmission images of the subject during HDR brachytherapy.

Technical note: Analysis of brachytherapy source movement by high-speed camera.

To assess the accuracy of the movement of a brachytherapy source using a high-speed camera for evaluating source position, dwell time, and transit dose. A high-speed camera was used to record the source position of an Ir-192 source relative to a ruler within a custom positioning jig in a remote afterloading system. The analyzed frames can be used to assess dwell positions and times. Treatment plans had multiple dwell times equal to 0.1, 0.5, 1.0, and 2.0 s in 2.5- and 5-mm step sizes. Images were acquired at a rate of 146 frames/s. Acquired images were processed to automatically track the actual source using the correlation between a template image and each frame. The brachytherapy dose calculation formalism (AAPM TG43-U1) was applied to each frame to evaluate the transit dose contribution to the total dose. The differences in measured source positions from the nominal for dwell times equal to 0.1, 0.5, 1.0, and 2.0 s in treatment plans were approximately ≤1mm. The corresponding differences in measured dwell times from the nominal values at 5 mm steps were -15, -9, -5, and 5 ms, respectively. The source velocities at 5mm steps were approximately 393mm/s. The dose differences at 5mm from the source movement with and without the transit dose for these dwell times were 38%, 7%, 3%, and 2%, respectively. Recording a brachytherapy source using a high-speed camera allowed the evaluation of positional and dwell time accuracies as well as dosimetry assessments, such as the transit dose, based on the application of AAPM TG-43U1.

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Determination of variation in dosimetric parameters of treatment planning with Co-60 and Ir-192 sources in high dose rate brachytherapy of cervical carcinoma

AimTo determine the differences in dosimetric parameters in patients of intracavitary brachytherapy and interstitial HDR brachytherapy using Co-60 and Ir-192 sources. Materials and methodsComputed tomography (CT) based treatment plans of 20 cervical carcinoma patients treated with intracavitary and interstitial high dose rate brachytherapy were retrospectively studied. Patients were planned using Co-60 and Ir-192 sources, keeping the same dwell positions and dose objectives. The dosimetric parameters such as V100, D90, homogeneity index (HI) and conformal index (CI) for target and D2cc, D1cc and D0.1cc for organs at risk (OAR) were compared for both sources. ResultsFor interstitial brachytherapy plans, HR-CTV mean V100 values for Co-60 and Ir-192-based plans were 97.03 ± 1.93% and 96.42 ± 2.18%, respectively. There was no significant difference found in target coverage (p = 0.370). Ir-192 based plans were more homogeneous (HI = 0.68 ± 0.09) than the Co-60 plans (HI = 0.59 ± 0.10). However, the conformity was similar with both the sources. No significant difference was found between D2cc, D1cc, and D0.1cc values of bladder and rectum. In intracavitary brachytherapy plans, we did not find any significant difference in the dosimetric parameters such as point A values, D90, V100, and OAR doses on comparing plans from both sources. ConclusionThere are no significant differences in dosimetric parameters and no clinical advantage of using Co-60 over Ir-192-based brachytherapy. However, when it comes to cost management, Co-60 has a longer half-life, which reduces the cost of frequent source replacement and disposal.

Evaluating dosimetric accuracy of the 6 MV calibration on EBT3 film in the use of Ir-192 high dose rate brachytherapy.

PurposeTo evaluate the dosimetric accuracy of EBT3 film calibrated with a 6 MV beam for high dose rate brachytherapy and propose a novel method for direct film calibration with an Ir‐192 source.MethodsThe 6 MV calibration was performed in water on a linear accelerator (linac). The Ir‐192 calibration was accomplished by irradiating the film wrapped around a cylinder applicator with an Ir‐192 source. All films were scanned 1‐day post‐irradiation to acquire calibration curves for all three (red, blue, and green) channels. The Ir‐192 calibration films were also used for single‐dose comparison. Moreover, an independent test film under a H.A.M. applicator was irradiated and the 2D dose distribution was obtained separately for each calibration using the red channel data. Gamma analysis and point‐by‐point profile comparison were performed to evaluate the performance of both calibrations. The uncertainty budget for each calibration system was analyzed.ResultsThe red channel had the best performance for both calibration systems in the single‐dose comparison. We found a significant 4.89% difference from the reference for doses <250 cGy using the 6 MV calibration, while the difference was only 0.87% for doses >600 cGy. Gamma analysis of the 2D dose distribution showed the Ir‐192 calibration had a higher passing rate of 91.9% for the 1 mm/2% criterion, compared to 83.5% for the 6 MV calibration. Most failing points were in the low‐dose region (<200 cGy). The point‐by‐point profile comparison reported a discrepancy of 2%–3.6% between the Ir‐192 and 6 MV calibrations in this low‐dose region. The linac‐ and Ir‐192‐based dosimetry systems had an uncertainty of 4.1% (k = 2) and 5.66% (k = 2), respectively.ConclusionsDirect calibration of EBT3 films with an Ir‐192 source is feasible and reliable, while the dosimetric accuracy of 6 MV calibration depends on the dose range. The Ir‐192 calibration should be used when the measurement dose range is below 250 cGy.

Development and evaluation of a thallium (I) bromide dosimeter for intracavitary radiotherapy quality assurance

In intracavitary radiotherapy, incorrect source locations can result in excessive doses to normal tissues. Therefore, it is essential to accurately evaluate the source location. In this study, we investigated a digital line dosimeter based on thallium (I) bromide (TlBr) to improve the existing analogue verification method. Therefore, a polycrystalline TlBr unit cell dosimeter was manufactured, and the measurement performance of iridium-192 (Ir-192) sources was evaluated. We found that the dosimeter's reproducibility satisfied the evaluation criteria of 1.5% with a relative standard deviation of 1.44%. Moreover, the linearity showed excellent results (linear coefficient, R 2 = 0.9999). The distance dependence showed a difference of 0.03 cm at 50% intensity when compared to the inverse square value, whereas the angular dependence showed a large difference when compared to a diode. As the angle increased, the intensity gradually decreased, resulting in a difference of up to 41.9%. These results demonstrate the excellent performance of the TlBr dosimeter. However, because of the significant influence of angular dependence, a measurement distance that minimises this error should be applied when manufacturing line dosimeters in the future.

Near-IR and X-Ray Variability of Cyg X-3: Evidence for a Compact IR Source and Complex Wind Structures

Abstract We study near-infrared (JHK) and X-ray light curves of Cyg X-3 obtained with the 2.5 m telescope of the Caucasian Mountain Observatory of MSU SAI and collected from the RXTE ASM and MAXI archives. The light curves in the X-ray and IR domains are strongly affected by irregular variations. However, the mean curves are remarkably stable and qualitatively similar in both domains. This means that the IR flux of the system originates not only from the free–free radiation of the Wolf–Rayet (WR) wind but also from a compact IR source located near the relativistic companion. The shape of the mean X-ray and IR light curves suggest the existence of two additional structures in the WR wind—a bow shock near the relativistic companion and a so-called “clumpy trail.” Modeling of the mean X-ray and IR light curves allowed us to obtain important system parameters: the orbital phase of the superior conjunction of the relativistic companion ϕ 0 = −0.066 ± 0.006, the orbital inclination angle i = 29.°5 ± 1.°2, and the WR mass-loss rate M ̇ = ( 0.96 ± 0.14 ) × 10 − 5 M ⊙ yr − 1 . By using relations between M ̇ and the rate of the period change and between M ̇ and the WR mass, we estimated the probable mass of the relativistic companion M C ≃ 7.2 M ⊙, which points toward the black hole hypothesis. However, this estimate is based on the assumption of a smooth WR wind. Considering the uncertainty associated with clumping, the mass-loss rate can be lower, which leaves room for the neutron star hypothesis.

Exploring the High-redshift PBH-ΛCDM Universe: Early Black Hole Seeding, the First Stars and Cosmic Radiation Backgrounds

Abstract We explore the observational implications of a model in which primordial black holes (PBHs) with a broad birth mass function ranging in mass from a fraction of a solar mass to ∼106 M ⊙, consistent with current observational limits, constitute the dark matter (DM) component in the universe. The formation and evolution of dark matter and baryonic matter in this PBH-Λ cold dark matter (ΛCDM) universe are presented. In this picture, PBH-DM mini-halos collapse earlier than in standard ΛCDM, baryons cool to form stars at z ∼ 15–20, and growing PBHs at these early epochs start to accrete through Bondi capture. The volume emissivity of these sources peaks at z ∼ 20 and rapidly fades at lower redshifts. As a consequence, PBH DM could also provide a channel to make early black hole seeds and naturally account for the origin of an underlying DM halo–host galaxy and central black hole connection that manifests as the M bh–σ correlation. To estimate the luminosity function and contribution to integrated emission power spectrum from these high-redshift PBH-DM halos, we develop a halo occupation distribution model. In addition to tracing the star formation and reionization history, it permits us to evaluate the cosmic infrared and X-ray backgrounds. We find that accretion onto PBHs/active galactic nuclei successfully accounts for the detected backgrounds and their cross-correlation, with the inclusion of an additional IR stellar emission component. Detection of the deep IR source count distribution by the James Webb Space Telescope could reveal the existence of this population of high-redshift star-forming and accreting PBH DM.

Dose Distribution of 192Ir HDR Brachytherapy Source Measurement using Gafchromic® EBT3 Film Dosimeter and TLD-100H

This study aims to measure the radial dose function and anisotropy function F(r, θ) of high Dose Rate (HDR) 192Ir source in a fabricated water-equivalent phantom using Gafchromic® EBT3 film and TLD-100H and to compare the results obtained with the MCNP5 calculated values. The phantom was fabricated using Perspex PMMA material. For, the EBT3 films with a required dimension and TLD-100H chips were placed at r=1, 2, 3, 5, and 10 cm from the source. The F(r, θ) measurements were carried out at r=1, 2, 3, 5, and 10 cm with the angle range from 10° to 170°. The result of from EBT3 film and TLD-100H was in good agreement (2.10%±1.99). Compared to MCNP5, the differences are within 0.31% to 11.47% for EBT3 film and 0.08% to 10.58% for TLD-100H. For the F(r, θ), an average deviation with the MCNP5 calculation is 4.94%±2.7. For both and F(r, θ), the effects are prominent at r=10 cm. At this distance, the response of both Gafchromic® EBT3 film and TLD-100H shows less sensitivity as the dose followed the inverse square law. This work demonstrates that Gafchromic® EBT3 film dosimeter and TLD-100H are suitable dosimeters in 192Ir dosimetric measurements at a radial distance of ˂5 cm

CONTEMPORARY APPROACHES TO PROGNOSTICATION AND MANAGEMENT OF PELVIC RADIATION INJURIES IN GYNECOLOGICAL CANCER PATIENTS.

Rapid development of radiotherapeutic techniques and implementation of radiation therapy (RT) nanotechnologies in practice, taking into account principles of radiobiology, ensures that the planned dose will bedelivered to the target volume with minimal irradiation of healthy tissues while maintaining the guaranteed RTquality. Therefore, further advance of RT involves not only implementation of the new technologies in radiationpractice, but also the intensive developments in fields of radiation medicine and clinical radiobiology. search for optimal models of the high-energy (HDR - high dose rate) brachytherapy (BT) using the 192Irsource in comparison with effects of the reference gamma radiation from 60Co, thereby, to increase the effectivenessof chemoradiation therapy (CRT) of gynecological cancer patients (GCPs) with minimal radiation loads on criticalorgans and tissues in the tumor environment. The radiobiological study was aimed to determine the feasibility ofusing the transmembrane potential (TMP) and intensity of reactive oxygen species (ROS) production in peripheralblood lymphocytes (PBL) as predictors of radiosensitivity of non-malignant cells from the tumor environment or itsbed in order to minimize the RT complications in GCPs. Patients (n = 115) with cancer stages II-III, T2-3N0-1M0 were managed with comprehensiveconservative treatment. Three groups of patients were selected depending on the applied HDR BT method against abackground of the administered chemosensitizing agents. Blood samples of GCPs (n = 24) before the RT initiationand of apparently healthy individuals (AHIs, i.e. the control group, n = 18) were taken for the radiobiologicalresearch. Review of the direct results of 60Co or 192Ir sources use in HDR BT and of the follow-up data showed theincreased tumor positive response in the main study groups after CRT course by respectively 16.6 % and 20.1 % incomparison with 60Со HDR BT administration. Concerning local reactions it was noted that grade II radiation reactions were almost absent in the main groups. According to the results of radiobiological studies, it was establishedthat TMP level in PBL of GCPs was 1.36 times higher than in AHIs. Thus, the emerging of late radiation injuries depended on the accuracy of of individual computer planning and correct reproduction of the planned RT course, timely correction of treatment programs, use of a complexof rational medical prophylaxis, severity of tumor process and concomitant disorders, as well as on the used type ofHDR radiation sources (192Ir and 60Co). Changes in TMP values and intensity of ROS production in PBL of GCPs in comparison with AHIs, and the high values of these parameters in PBL of individual patients are a rationale to specifythem as additional indicators characterizing the possibility of radiation complications before the RT planning.

Calculation of attenuation parameter for Ir-192 gamma source in shielding materials

Purpose:Calculation of photon attenuation is necessary for the selection of shielding materials for an irradiation facility.Methods and Materials:In this work, a Monte Carlo simulation was utilized to assess the effectiveness of clay-polyethylene mixture and clay as the radiation shielding materials for high-energy gamma sources (Ir-192). Ordinary concrete was also studied as the benchmark.Results:The calculated linear attenuation values for ordinary concrete are within 0.44% of the standard XCOM value for 380 keV photon. In the case of a multienergy Ir-192 gamma source, the calculated linear attenuation coefficient (μ) for ordinary concrete is 15.5% and 7.25% higher than clay and fabricated clay-polyethylene, respectively. Meanwhile, the μ value for fabricated clay-polyethylene is 8.3% higher than that of clay.Conclusion:In conclusion, a 10 cm thickness of clay and clay-polyethylene mixture is sufficient to attenuate 87% and 89% of photons from Ir-192 source. The calculated linear attenuation coefficients for the three shielding materials are also consistently higher, about 7.5%, than that of the XCOM value for 380 keV photon.

Intra-cavitary brachytherapy in endometrial carcinoma: experience with cobalt-60 source.

PurposeTo report vaginal cuff brachytherapy (VCB) dosimetry parameters and clinical outcomes of patients with localized endometrial cancer treated with adjuvant high-dose-rate (HDR) brachytherapy using a cobalt-60 (60Co) source.Material and methodsBetween 2011 and 2017, we identified patients with endometrial cancer treated with surgery and adjuvant VCB. Dosimetry variables analyzed included D2cc, D1cc, and D0.1cc for organs at risk (OARs) and distance from cylinder surface to 150% and 200% isodose line in vaginal mucosa. Local relapse (LR), regional relapse (RR), distant metastasis (DM), progression-free survival (PFS), and overall survival (OS) were analyzed using Kaplan-Meier, and log-rank test was applied to assess differences between groups. Toxicity evaluation was tested for possible cross-correlation within dosimetric parameters using Pearson r test and stepwise multivariate linear regression.ResultsWe identified 93 suitable patients. Mean age at diagnosis was 66 years (range, 45-85 years). Most patients had endometrioid adenocarcinoma (61.3%), followed by papillary-serous carcinoma (11.8%). 71% of patients presented with FIGO stage I (35.5% IA and 35.5% IB), 11.8% were stage II, and 17.2% were stage III. Adjuvant external beam radiotherapy (EBRT) (range, 46-50.4 Gy) was used in 53.8% of patients, and adjuvant chemotherapy in 38.7%. Median follow-up was 39 months (range, 5-84 months). Three-year OS and PFS were 87.5% and 85.5%, respectively. LR was seen in 2.2% of cases, RR in 7.5%, and DM in 12.9%. Mean rectum D2cc/D0.1cc were 88.1% and 116%, and mean bladder D2cc/D0.1cc were 79.2% and 103.2%, respectively. The most common acute toxicity was vaginal mucositis (8.9% ≥ G2), and the most frequent chronic toxicity was vaginal stenosis (25.3% ≥ G1).ConclusionsAdjuvant high-dose-rate VCB with 60Co source for patients with endometrial cancer is well tolerated, with clinical and toxicity outcomes comparable to those reported with iridium-192 (192Ir) source.

Monte Carlo Study on Dose Distributions Around 192Ir, 169Yb, and 125I Brachytherapy Sources Using EGSnrc-based egs_brachy User-code.

As per the recommendations of the American Association of Physicists in Medicine Task Group 43, Monte Carlo (MC) investigators should reproduce previously published dose distributions whenever new features of the code are explored. The purpose of the present study is to benchmark the TG-43 dosimetric parameters calculated using the new MC user-code egs_brachy of EGSnrc code system for three different radionuclides 192Ir, 169Yb, and 125I which represent high-, intermediate-, and low-energy sources, respectively. Brachytherapy sources investigated in this study are high-dose rate (HDR) 192Ir VariSource (Model VS2000), 169Yb HDR (Model 4140), and 125I -low-dose-rate (LDR) (Model OcuProsta). The TG-43 dosimetric parameters such as air-kerma strength, S k, dose rate constant, Λ, radial dose function, g(r) and anisotropy function, F(r,θ) and two-dimensional (2D) absorbed dose rate data (along-away table) are calculated in a cylindrical water phantom of mass density 0.998 g/cm3 using the MC code egs_brachy. Dimensions of phantom considered for 192Ir VS2000 and 169Yb sources are 80 cm diameter ×80 cm height, whereas for 125I OcuProsta source, 30 cm diameter ×30 cm height cylindrical water phantom is considered for MC calculations. The dosimetric parameters calculated using egs_brachy are compared against the values published in the literature. The calculated values of dose rate constants from this study agree with the published values within statistical uncertainties for all investigated sources. Good agreement is found between the egs_brachy calculated radial dose functions, g(r), anisotropy functions, and 2D dose rate data with the published values (within 2%) for the same phantom dimensions. For 192Ir VS2000 source, difference of about 28% is observed in g(r) value at 18 cm from the source which is due to differences in the phantom dimensions. The study validates TG-43 dose parameters calculated using egs_brachy for 192Ir, 169Yb, and 125I brachytherapy sources with the values published in the literature.

RSC: Dosimetry in high-dose-rate brachytherapy with a radio-fluorogenic gel dosimeter

A nanoclay-based radio-fluorogenic gel (NC-RFG) was used to verify the source position and dose distribution in high-dose-rate (HDR) brachytherapy. The dose response confirmed linearity up to 60 Gy. The source position could be detected with an accuracy of ≤0.3 mm, and the dose distribution near the Ir-192 source showed good agreement with the Monte Carlo simulation. NC-RFG can be expected to be a quality assurance tool suitable for the evaluating the dose distribution in HDR brachytherapy.

DEVELOPMENT OF 5 DOF ROBOTIC ARM PROTOTYPE CONTROL SYSTEM IN BRACHYTHERAPY PREPARATION BASED ON ARTIFICIAL NEURAL NETWORK

Brachytherapy is a cancer treatment that uses radioactive sources with temporary or permanent implantation in cancer tissue. The theraphy uses a radioactive Ir-192 source wrapped in a stainless steel capsule with a diameter of 0.5 mm and a length of 4 mm. The Center for Radioisotopes and Radiopharmaceutical Technology applies a remote manipulator to manufacture microcapsules, which affects the accuracy and risks of the radiation received by the operator. Therefore, to solve this problem, it is necessary to design a 5 DoF robotic arm based on artificial neural networks as a radioactive source transfer tool to improve the precision and safety of operators in preparing the radioactive sources. In developing the 5 DoF robotic arm control system, the NImyRIO was employed, which can control the servo motor, relay pump and valve reality, image processing, and inverse kinematic. The inverse kinematic uses the neural network method with a forward kinematic validation. The inverse kinematic test obtains the RMSE value of 2.78932 for x, 5.05205 for y, and 12.641 for z in the inverse kinematic test of artificial neural networks. Therefore, the inverse kinematic accuracy of the artificial neural network needs to be redeveloped.

Infrared multiple photon dissociation (IRMPD) spectroscopy and its potential for the clinical laboratory

Infrared multiple photon dissociation (IRMPD) spectroscopy is a powerful tool used to probe the vibrational modes–and, by extension, the structure—of an ion within an ion trap mass spectrometer. Compared to traditional FTIR spectroscopy, IRMPD spectroscopy has advantages including its sensitivity and its relative ability to handle complex mixtures. While IRMPD has historically been a technique for fundamental analyses, it is increasingly being applied in a more analytical fashion. Notable recent demonstrations pertinent to the clinical laboratory and adjacent interests include analysis of modified amino acids/residues and carbohydrates, structural elucidation (including isomeric differentiation) of metabolites, identification of novel illicit drugs, and structural studies of various biomolecules and pharmaceuticals. Improvements in analysis time, coupling to commercial instruments, and integration with separations methods are all drivers toward the realization of these analytical applications. Additional improvements in these areas, along with advances in benchtop tunable IR sources and increased cross-discipline collaboration, will continue to drive innovation and widespread adoption. The goal of this tutorial article is to briefly present the fundamentals and instrumentation of IRMPD spectroscopy, as an overview of the utility of this technique for helping to answer questions relevant to clinical analysis, and to highlight limitations to widespread adoption, as well as promising directions in which the field may be heading.

A small-scale realistic inter-laboratory accident dosimetry comparison using the TL/OSL from mobile phone components

An inter-laboratory comparison of a small-scale field experiment was conducted in the framework of the Korea retrospective dosimetry network (KREDOS) to verify the reliability and compatibility of thermoluminescence and optically stimulated luminescence techniques for accident dosimetry. Three institutes participated in this comparison, including the Korea Atomic Energy Research Institute, the Korea Institute of Nuclear Safety and the University of Salzburg. Two adult CIRS torso phantoms were used as virtual subjects exposed to a high-activity Ir-192 source, developing both homogeneous and inhomogeneous exposures in a shielded enclosure. The target materials for dose estimation were mobile phone components, such as resistors, display glasses, and chip cards. LiF:Mg,Cu, Si thermoluminescent (TL) detectors were used as reference dosimeters. The mobile phones were attached to the chest, hip, and thighs of the anthropomorphic phantoms. The measured doses ranged from 100 mGy to 2 Gy, depending on the position of the mobile phone on the phantom. The proficiency of the dose assessment was tested at three laboratories. Using the applied protocols, the local dose distribution on the display glasses was unclear, but the distribution around the body was confirmed.

The Dose Distribution from Iridium-192 Source on Cervical Cancer Brachytherapy by Manchester System Using Monte Carlo Simulation

One treatment for cervical cancer is to use radioactive sources that directly target the cancer cell called brachytherapy. This study is aimed to determine dose distribution at phantom pelvis using the DOSXYZnrc Monte Carlo code. The phantom was derived from a CT scan image of the DICOM-type pelvis with a size of 50 × 50 × 28.8 cm obtained from Santosa Kopo Hospital. The source used was Ir-192, which makes an asymmetrical beam with a size of 0.45 × 0.09 × 0.09 cm. Monte Carlo simulation was performed to determine the dose distribution of the Ir-192 source on cervical cancer CT images based on the Manchester system. The Monte Carlo simulation was divided into two models with distance variations on the applicator. Model A used TPS data with a distance between sources of 0.9 cm, while model B had a distance between sources of 0.5 cm. The distribution of dose resulting from the Monte Carlo simulation was analyzed and compared with TPS data. The results showed that at the range of 50 %, dose distribution in model A reaches the end of 3.9 cm. When compared to the range of 50 % dose distribution at the TPS results that reaches the point of 4 cm, it produces a deviation value of 2.5 %, which is still within the tolerance range. Model A and Model B provide different dose distribution. In model B, it reaches 3.86 cm, resulting in a deviation of 1.02 %, which is still within the tolerance range. The resulting γ-index value for the 50 % dose distribution was 2.26, while the whole area's GPR value was 94.13 %. This indicates a difference in dose distribution between the two models. Therefore, the smaller the distance between the sources, the shorter the dose distribution range with relatively more uniform dose distribution.

Metallo-dielectric metasurfaces for thermal emission with controlled spectral bandwidth and angular aperture

We introduce thermal metallo-dielectric metasurfaces as mid IR sources. The emitter is a lossy metal. The spectral and angular emission is controlled using a periodic array of high refractive dielectric resonators. We introduce a design that allows to control independently the emission bandwidth and the angular aperture while ensuring a large emissivity. To validate the concept, we fabricated and characterized a metasurface, showing a good agreement with the theory.

Development of a simultaneous imaging system to measure the optical and gamma ray images of Ir-192 source for high-dose-rate brachytherapy

In high-dose-rate (HDR) brachytherapy, verification of the Ir-192 source's position during treatment is needed because such a source is extremely radioactive. One of the methods used to measure the source position is based on imaging the gamma rays from the source, but the absolute position in a patient cannot be confirmed. To confirm the absolute position, it is necessary to acquire an optical image in addition to the gamma ray image at the same time as well as the same position. To simultaneously image the gamma ray and optical images, we developed an imaging system composed of a low-sensitivity, high-resolution gamma camera integrated with a CMOS camera. The gamma camera has a 1-mm-thick cerium-doped yttrium aluminum perovskite (YAIO3: YAP(Ce)) scintillator plate optically coupled to a position-sensitive photomultiplier (PSPMT), and a 0.1-mm-diameter pinhole collimator was mounted in front of the camera to improve spatial resolution and reduce sensitivity. We employed the concept of a periscope by placing two mirrors tilted at 45 degrees facing each other in front of the gamma camera to image the same field of view (FOV) for the gamma camera and the CMOS camera. The spatial resolution of the imaging system without the mirrors at 100 mm from the Ir-192 source was 3.2 mm FWHM, and the sensitivity was 0.283 cps/MBq. There was almost no performance degradation observed when the mirrors were positioned in front of the gamma camera. The developed system could measure the Ir-192 source positions in optical and gamma ray images. We conclude that the developed imaging system has the potential to measure the absolute position of an Ir-192 source in real-time clinical measurements.