IR Source Research Articles

Precise determination of thermal parameters of a microbolometer

Determination of microbolometer thermal properties such as thermal capacitance, conductance, time constant, and IR responsivity is of the utmost importance as they directly influence microbolometer performance. Here we show a technique to measure them by using a minimized self-heating effect, thus leading to their precise determination via measurements based on an AC-biased Wheatstone bridge containing a microbolometer. The bridge outputs were subtracted from each other by a differential voltage preamplifier with its output processed by a lock-in amplifier. The lock-in amplifier output as a function of the amplitude of AC bias provided an amplitude of microbolometer thermal conductivity. A microbolometer temperature response to pulse irradiation of its membrane provided the value of its thermal time constant and, thus, its thermal capacitance. Finally, we also extracted microbolometer responsivity using a blackbody IR source. The method was experimentally verified using a micromachined bolometer, which showed excellent agreement with the analytical solution.

Theoretical rationale and identification of heat and mass transfer processes in vibration dryers with IR-energy supply

The paper contains theoretical substantiation of the processes of radiation-convective heat and mass transfer between all the defining objects inside the vibration dryer with IR energy supply. The presented equations, developed on the basis of the heat and material balance, describe the basic dynamic characteristics of the drying mode for oil-bearing grain material in a continuously operating IR dryer.Since there is no exact analytic solution of the presented mathematical model shaped as a system of differential equations with partial derivatives, the authors propose an approximate solution. The latter allows identifying the dependences between the distribution of temperature and moisture content of grain and oil-containing materials along the length of the dryer for any moment of time.The numerical solution of the reduced mathematical model is possible only with the presence of certain interconnected kinetic coefficients. The kinetic coefficients can not be found experimentally by direct measurements; therefore, the article proposes a method to overcome these difficulties. The presented approximate analytical solution of the synthesized mathematical model, with the use of the method of inverse problems, has allowed determining sets of coefficients by the results of the experimental identification of dehydration. In the future, experimentally identified parametric complexes of the model can be used in the analysis of the drying process for approximate solutions or for further exact numerical solution.Experimental studies of dehydration of grain material have proved that when the power of an IR source is increased from 400 to 500 W, the time for drying from the initial moisture content of 11 % to 8.75 % decreases from 9 to 7 minutes. It is determined that the Rebinder effect characterizing the dampness and thermal properties of the material decreases with a decrease in the moisture content from 0.04 at 11 % to 0.01 at 9 %. This is interesting from the practical point of view as the obtained results and the developed mathematical model can be used for increasing the energy efficiency of the processes of thermal drying in typical facilities that prepare oil-bearing grain materials for their processing.

Automated source tracking with a pinhole imaging system during high-dose-rate brachytherapy treatment

The transportation accuracy of sealed radioisotope sources influences the therapeutic effect of high-dose-rate (HDR) brachytherapy. We have developed a pinhole imaging system for tracking an Ir-192 radiation source during HDR brachytherapy treatment. Our system consists of a dual-pinhole collimator, a scintillator, and a charge-coupled device (CCD) camera. We acquired stereo-shifted images to infer the source position in three dimensions using a dual pinhole collimator with 1.0 mm diameter pinholes. The CCD camera captured consecutive images of scintillation light that corresponds to the source positions every 2 s. The system automatically tracks scintillation light points using template-matching technique and measured the source positions therefrom. By integrating a series of CCD images, we could infer the source dwell time from the pixel values in the integrated image.We investigated the tracking accuracy of our system in monitoring simulated brachytherapy as it would be performed for cervical cancer by using water as a stand-in for human tissue. Ir-192 pellet was moved through a water tank using tandem and ovoid applicators. The CCD camera captured clear images of the scintillation light produced by the underwater Ir-192 source in conditions equivalent to common clinical situations. The differences between the measured and the reference 3D source positions and dwell times were 1.5 ± 0.7 mm and 0.8 ± 0.4 s, respectively.This system has the potential to track in vivo Ir-192 source in real time and may prove a useful tool for quality assurance during HDR brachytherapy treatments in clinical settings.

Impact of different Ir-192 source models on dose calculations in high-dose-rate brachytherapy.

In high-dose-rate brachytherapy, the geometry of the radioactive source is sometimes updated. Some institutions use a different source model for the dose calculation in treatment planning and treatment. The effects of this discrepancy were examined for four types of treatment plans, and ten patients were selected for each treatment plan. The impact of different source models depended on the types of treatment plan, patients, and dose index. To reduce the uncertainty and improve the reliability of the data, it would be better to use more robust metrics (D90 and D2cc) for treatment planning evaluation in facilities with this problem.

Convective losses of thermal infrared emitters with cantilevered heating elements

Non-dispersive infrared- (NDIR-) gas sensors usually consist of a thermal infrared emitter, a tube and a pyroelectric detector with a filter that is transparent to the characteristic wavelength of the gas to be detected. Since pyroelectric sensors are only sensitive to alternating radiation, the radiation must be modulated. This is easiest to achieve by electrical modulation of the emitter. Under this cyclic excitation the thermodynamic properties of the IR source affect the emitted infrared radiation and, in consequence, the sensor signal. Optimal gas sensor operations (e.g. with regard to gas measurement resolution) require to know which factors influence the thermodynamic properties of thermal emitters. In the course of miniaturization and with regard to portable use, gas measuring devices must also become more compact and energy-efficient. Consequently, the radiation source must have low power consumption and high (radiation) efficiency. The heating and cooling curves measured during electrical (square-wave) modulation contain all information about the thermal losses of real emitters and, therefore, about their energy efficiency as well. In this paper, a thermodynamic model of an infrared emitter will be introduced, which also includes all thermal losses (radiation, heat conduction and convection in the filling gas). The comparison of the measured and calculated heating and cooling curves allows to quantify the thermal losses of the emitter and to draw conclusions about its energy efficiency. As a result, this paper reveals that the majority of the electrical energy supplied is dissipated into the filling gas by convection and heat conduction, which significantly reduces the energy efficiency of the radiation source. Vacuum measurements confirm this assumption and support the model.

Comparison of Yb169, Ir192, and Co60 Hdr Sources for Use with a Conventional Tandem and Ring Applicator for Cervical Cancer Treatment

Comparison of Yb169, Ir192, and Co60 Hdr Sources for Use with a Conventional Tandem and Ring Applicator for Cervical Cancer Treatment

Alternative Approach to Calibrate Hdr Ir192 Source

Alternative Approach to Calibrate Hdr Ir192 Source

Direction modulated brachytherapy (DMBT) tandem applicator for cervical cancer treatment: Choosing the optimal shielding material.

To investigate the dose modulation capability of a novel MRI-compatible direction modulated brachytherapy (DMBT) tandem applicator design with various high-density shielding materials for brachytherapy treatment of cervical cancer. The shield materials that have been evaluated are tantalum (Ta), pure tungsten (W), gold (Au), rhenium (Re), osmium (Os), platinum (Pt), iridium (Ir), and W' tungsten alloy (95%W, 3.5%Ni, 1.5%Cu). The recently proposed six-channel DMBT tandem is composed of nonmagnetic tungsten alloy (W') rod with diameter of 5.4mm and coated with 0.3-mm thick bio-safe plastic sheath. The tandem shielding material can, however, be individually replaced with various other shields to create directional radiation. Monte Carlo N-Particle (MCNP) code was used to calculate the three-dimensional (3D) dose distributions in a water phantom for an HDR 192 Ir (mHDR-v2) source inside each DMBT tandem with various shields and a plastic conventional tandem (Con.T). Then, the 3D dose distributions were imported into an in-house-coded inverse planning optimization algorithm to obtain optimal plans for 12 clinical cases chosen at random from the international RetroEMBRACE dataset involving conventional tandem and ring (Con.T&R) applicators. All plans generated by the DMBT tandem and ring (DMBT&R) with the tungsten alloy [DMBT(W')&R] were compared with the corresponding Con.T&R plans, to generate benchmark results. These benchmark results were then considered as reference plans for other shields performances. Plans were normalized to receive the same high-risk clinical target volume (CTVHR ) D90 . The D100 , D10 , and V100 for CTVHR , and D2cm3 for organs at risk (OARs) of bladder, sigmoid, and rectum were calculated and compared. Transmission factor (TF), that is, the dose in the backside of the DMBT shield over that in the front opening, at a 5cm distance, were 36.6%, 34.8%, 31.9%, 28.9%, 27.9%, 26.2%, 26.2%, and 25.5%, for Ta, W', W, Re, Au, Os, Pt, and Ir shields, respectively. On average, the CTVHR values for D100 , V100 , D10 were not significantly different across all DMBT&R shields and the Con.T&R plans (P>0.219). For the D2cm3 , the benchmark results showed significant reductions (P<0.03), that is, on average, -8.3% for bladder, -10.7% for rectum, and -10.1% for sigmoid, compared to the Con.T&R plans. However, the various shields showed little improvement from the tungsten alloy (W'), where on average, rectum (bladder) [sigmoid] D2cm3 were reduced by -1.32% (-0.85%) [-1.01%], -1.25% (-0.78%) [-0.91%], -1.22% (-0.75%) [-0.86%], -0.94% (-0.60%) [-0.70%], -0.84% (-0.51%) [-0.59%], and -0.38% (-0.24%) [-0.23%] for Ir, Pt, Os, Au, Re, and W shields, relative to the benchmark W' DMBT plans, respectively. These corresponding values for Ta increased by +0.28% (+0.08%) [+0.25%], respectively. The Ir, Pt, Os, Au, Re, and W shielding materials, respectively, in descending order, lead to better OAR sparing than the DMBT(W')&R plans. However, the amount of improvement is limited and clinically insignificant. This finding suggests that the initial W' shield remains a suitable choice given the proven MR compatibility, for use in MR-guided adaptive brachytherapy of cervical cancer.

Relativistic single-cycle tunable infrared pulses generated from a tailored plasma density structure

The availability of intense, ultrashort coherent radiation sources in the infrared region of the spectrum is enabling the generation of attosecond X-ray pulses via high harmonic generation, pump-probe experiments in the "molecular fingerprint" region and opening up the area of relativistic-infrared nonlinear optics of plasmas. These applications would benefit from multi-millijoule single-cycle pulses in the mid to long wavelength infrared (LW-IR) region. Here we present a new scheme capable of producing tunable relativistically intense, single-cycle infrared pulses from 5-14$\mu$m with a 1.7% conversion efficiency based on a photon frequency downshifting scheme that uses a tailored plasma density structure. The carrier-envelope phase (CEP) of the LW-IR pulse is locked to that of the drive laser to within a few percent. Such a versatile tunable IR source may meet the demands of many cutting-edge applications in strong-field physics and greatly promote their development.

A quality assurance device for measuring afterloader performance and transit dose for nasobiliary high-dose-rate brachytherapy

PurposeNasobiliary high-dose-rate (HDR) brachytherapy has emerged as an effective tool to boost the radiation dose for patients with unresectable perihilar cholangiocarcinoma. This work describes a quality assurance (QA) tool for measuring the HDR afterloader's performance, including the transit dose, when the source wire travels through a tortuous nasobiliary catheter path. Methods and MaterialsThe nasobiliary QA device was designed to mimic the anatomical path of a nasobiliary catheter, including the nasal, stomach, duodenum, and bile duct loops. Two of these loops, the duodenum and bile duct loops, have adjustable radii of curvature, resulting in the ability to maximize stress on the source wire in transit. The device was used to measure the performance over time for the HDR afterloader and the differences between intraluminal catheter lots. An upper limit on the transit dose was also measured using radiochromic film and compared with a simple theoretical model. ResultsThe QA device was capable of detecting performance variations among nasobiliary catheter lots and following radioactive source replacement. The transit dose from a nasobiliary treatment increased by up to one order of magnitude when the source wire encountered higher than normal friction. Three distinct travel speeds of the source wire were observed: 5.2, 17.4, and 54.7 cm/s. The maximum transit dose was 0.3 Gy at a radial distance of 5 mm from a 40.3 kU 192Ir source. ConclusionsThe source wire encounters substantially greater friction when it navigates through the nasobiliary brachytherapy catheter. A QA tool that mimics the nasal, stomach, duodenum, and bile duct loops may be used to evaluate transit dose and the afterloader's performance over time.

Does the apex optimization line matter for single-channel vaginal cylinder brachytherapy planning?

The objective of this study is to test the impact of the use of the apex optimization line for new vaginal cylinder (VC) applicators. New single channel VC applicators (Varian) that have different top thicknesses but the same diameters as the old VC applicators (2.0 cm diameter, 2.3, 2.6, 3.0, and 3.5 cm) were compared using phantom studies. Old VC applicator plans without the apex optimization line were also compared to the plans with an apex optimization line. The apex doses were monitored at 5 mm depth doses (eight points) where a prescription dose (Rx) of 6 Gy was prescribed. VC surface doses (eight points) were also analyzed. The new VC applicator plans without apex optimization line presented significantly lower 5‐mm depth doses over the Rx (on average −31 ± 7%, P < 0.00001) due to thicker VC tops (3.4 ± 1.1 mm thicker with the range of 1.2–4.4 mm) than the old VC applicators. Old VC applicator plans also showed a statistically significant reduction (P < 0.00001) due to the Ir‐192 source anisotropic effect at the apex region, but the percent reduction over the Rx was only −7 ± 9%. However, by adding the apex optimization line to the new VC applicator plans, the plans improved 5‐mm depth doses (−7 ± 9% over Rx) that were not statistically different from old VC applicator plans (P = 0.923), along with apex VC surface doses (−22 ± 10% over old VC vs −46 ± 7% without using apex optimization line). The use of the apex optimization line is important in order to avoid significant additional cold doses (−24 ± 2%) at the prescription depth (5 mm) of the apex, specifically for the new VC applicators that have thicker tops. A template‐based vaginal cylinder planning reduced the intra‐ and inter‐planner variations of manual generation of apex optimization line, along with treatment time.

Radiobiological Characterization of the Radiosensitization Effects by Gold Nanoparticles for Megavoltage Clinical Radiotherapy Beams

Gold nanoparticles (AuNPs) have been experimentally proven to induce radiosensitization effects particularly for kilovoltage photon beam. Theoretically, AuNPs bombarded with kilovoltage photon beam would increase the photoelectric interactions cross section and hence increase cell death. Despite the intriguing finding, this type of beam is not common in clinical radiotherapy and possesses limited application compare to megavoltage beams. In this study, quantification of the radiosensitization effects acquired from clinical megavoltage photon, electron, and high-dose rate (HDR) gamma rays from Ir-192 source were conducted. In addition, radiobiological characterization of the cell survival curves that are commonly described by linear-quadratic (LQ) model was also evaluated using multi-target (MT) and repairable conditionally repairable (RCR) model. Significant sensitization enhancement ratios (SER) were obtained particularly for 15 MeV electron beams in which the amplification of radiation effects by AuNPs is up to the factor of 1.78. The results also demonstrate validity of experimental models to describe the cell survival curve and determine the radiosensitization effects. However, slight variation was observed for SER values computed from each model which indicate the importance to specify the quantification method. Adoption of radiobiological models and their parameters could also be employed as indicator to explain the mechanistic events in the AuNPs’ radiosensitization effects. As conclusion effective radiosensitization by megavoltage clinical radiotherapy beams could be achieved and precise radiobiological characterization drawn from radiobiological models may provide insight towards radiobiological impacts induced by AuNPs.

Monte Carlo study of out-of-field exposure in carbon-ion radiotherapy with a passive beam: Organ doses in prostate cancer treatment

PurposeThe aim of this work was to estimate typical dose equivalents to out-of-field organs during carbon-ion radiotherapy (CIRT) with a passive beam for prostate cancer treatment. Additionally, sensitivity analyses of organ doses for various beam parameters and phantom sizes were performed. MethodsBecause the CIRT out-of-field dose depends on the beam parameters, the typical values of those parameters were determined from statistical data on the target properties of patients who received CIRT at the Heavy-Ion Medical Accelerator in Chiba (HIMAC). Using these typical beam-parameter values, out-of-field organ dose equivalents during CIRT for typical prostate treatment were estimated by Monte Carlo simulations using the Particle and Heavy-Ion Transport Code System (PHITS) and the ICRP reference phantom. ResultsThe results showed that the dose decreased with distance from the target, ranging from 116 mSv in the testes to 7 mSv in the brain. The organ dose equivalents per treatment dose were lower than those either in 6-MV intensity-modulated radiotherapy or in brachytherapy with an Ir-192 source for organs within 40 cm of the target. Sensitivity analyses established that the differences from typical values were within ∼30% for all organs, except the sigmoid colon. ConclusionsThe typical out-of-field organ dose equivalents during passive-beam CIRT were shown. The low sensitivity of the dose equivalent in organs farther than 20 cm from the target indicated that individual dose assessments required for retrospective epidemiological studies may be limited to organs around the target in cases of passive-beam CIRT for prostate cancer.

Feasibility of dose enhancement assessment: Preliminary results by means of Gd-infused polymer gel dosimeter and Monte Carlo study

This work reports the experimental development of an integral Gd-infused dosimeter suitable for Gd dose enhancement assessment along with Monte Carlo simulations applied to determine the dose enhancement by radioactive and X-ray sources of interest in conventional and electronic brachytherapy. In this context, capability to elaborate a stable and reliable Gd-infused dosimeter was the first goal aimed at direct and accurate measurements of dose enhancement due to Gd presence. Dose-response was characterized for standard and Gd-infused PAGAT polymer gel dosimeters by means of optical transmission/absorbance. The developed Gd-infused PAGAT dosimeters demonstrated to be stable presenting similar dose-response as standard PAGAT within a linear trend up to 13 Gy along with good post-irradiation readout stability verified at 24 and 48 h. Additionally, dose enhancement was evaluated for Gd-infused PAGAT dosimeters by means of Monte Carlo (PENELOPE) simulations considering scenarios for isotopic and X-ray generator sources. The obtained results demonstrated the feasibility of obtaining a maximum enhancement around of (14 ± 1)% for 192Ir source and an average enhancement of (70 ± 13)% for 241Am. However, dose enhancement up to (267 ± 18)% may be achieved if suitable filtering is added to the 241Am source. On the other hand, optimized X-ray spectra may attain dose enhancements up to (253 ± 22) %, which constitutes a promising future alternative for replacing radioactive sources by implementing electronic brachytherapy achieving high dose levels.

Physics elements of an algorithm for brachytherapy dose calculation in homogeneous media for 192Ir source

Unlike for external beam treatment, Model Based Dose Calculation Algorithms for Brachytherapy are still under development, and have been recently encouraged by the American Association of Physicists in Medicine. This delay is at least partially caused by the extreme complications associated with the multidimensional considerations underlying Brachytherapy dose calculations. These algorithms require detailed mathematical description, based on extensive radiation physics considerations, of the spatial and angular distribution of the points where the decay photon first interacts in matter, called TERMA points, along with the functions describing the radial and angular dose spread around each TERMA point, called Kernel. This work contributes to this global effort by providing these functions for the individual photon lines in the decay of the exactly modeled Nucletron microSelectron v3192Ir source. The underlying physics of all photon and electron interaction mechanisms has been extensively considered. Furthermore, the effect of the absorbing media has been also investigated. Ultimately, three-dimensional integration of dose Kernel contribution at a specified position, running all over TERMA points in the irradiated volume, has been conducted to generate the dose at that specific location. This methodology is much less time, data storage, and CPU consuming compared to repeating the extensive Monte Carlo simulations. The work is merely intended to provide a launching point and basic key physics elements for anticipated future quantitative clinical use.

PO-1021: HDR Brachytherapy dosimetry: clinical use of micro-silica bead TLD &amp; Gafchromic EBT3 film

Purpose or Objective To develop a novel high resolution experimental method for validating Monte Carlo-derived TG-43 brachytherapy source data, and model-based treatment planning systems. Experimental verification is recommended in the “Report of the High Energy Brachytherapy Source Dosimetry (HEBD) Working Group, 2012”, however, the steep dose gradients with a wide dynamic dose range and rapid change in dose rate has been a limitation for the ability of common detectors to obtain accurate measurements. In this study, we tested a micro silica bead TLDs recently developed at University of Surrey for suitability to perform accurate dose measurements around 60Co and 192Ir clinical HDR brachytherapy sources. The micro silica beads proven dosimetric characteristics (independency from dose rate and angle of radiation incidence) accompanied by small ‘donut shape’ physical dimensions (1.2 mm diameter and 0.9 mm thickness (Fig. 1 (a)) along with chemically inert nature, ease of use and reusability were considered as a very promising detectors for this application. Material and Methods Novel dosimeter positioning templates were designed and produced using AutoCAD software. The micro silica bead TLDs were threaded using cotton yarns and stitched onto the template to accurately position the dosimeters within ± 0.1 mm, in a full-scatter water tank (Fig 1(b) and 1(c)). Measurement setup for radial dose distribution and dose linearity is shown on (Fig 1(c)) and (Fig 1(b)). The used dose rates were form 10 to 4000 cGy/min and dose ranged from 0.5 to 40 Gy. The results of dose distribution measurements around the sources were compared to TG- 43 tabulated data and simultaneously irradiated EBT3 Gafchromic film. A TOLADO TL system was employed for read out of the TLDs. Triple-channel dosimetry using FilmQAPro with uncertainty reduction technique was used for film dosimetry Results The novel experimental method suitably addressed the dosimetry challenges. A linear dose response was observed in the investigated range, 0.5–40 Gy, with a correlation coefficient of R2 > 0.999. The ability of detector to assess the high gradient dose distribution with variable dose rate within the range of 10–4000 cGy/min around the sources was compared to the TG-43 data to that of EBT3 film and found to be within experimental uncertainty (Fig 2 (a) and (b)). Conclusion A novel, high spatial resolution experimental method was developed for validating brachytherapy dosimetry using micro silica bead TLDs on high precision templates. The measured radial dose distributions around both of the 60Co and 192Ir sources were comparable within the experimental uncertainty to the relevant TG-43 data and superior to that of EBT3 Gafchromic film measurement in terms of the dynamic dose range evaluated. The experimental method presented is suitable to address the challenge of HDR brachytherapy dosimetry.

Validating Fricke dosimetry for the measurement of absorbed dose to water for HDR 192Ir brachytherapy: a comparison between primary standards of the LCR, Brazil, and the NRC, Canada

Two Fricke-based absorbed dose to water standards for HDR Ir-192 dosimetry, developed independently by the LCR in Brazil and the NRC in Canada have been compared. The agreement in the determination of the dose rate from a HDR Ir-192 source at 1 cm in a water phantom was found to be within the k = 1 combined measurement uncertainties of the two standards: DNRC/DLCR = 1.011, standard uncertainty = 2.2%. The dose-based standards also agreed within the uncertainties with the manufacturer’s stated dose rate value, which is traceable to a national standard of air kerma. A number of possible influence quantities were investigated, including the specific method for producing the ferrous-sulphate Fricke solution, the geometry of the holder, and the Monte Carlo code used to determine correction factors. The comparison highlighted the lack of data on the determination of G(Fe3+) in this energy range and the possibilities for further development of the holders used to contain the Fricke solution. The comparison also confirmed the suitability of Fricke dosimetry for Ir-192 primary standard dose rate determinations at therapy dose levels.

Determination of a beam quality conversion factor from 60Co to 192Ir

Radiation dosimetry is an integral part of the radiation therapy process. The ultimate goal of radiation dosimetry is to determine the dose delivered to the tumor and to the normal tissues in a patient undergoing radiotherapy. The importance of HDR 192Ir brachytherapy as the main mode of treatment calls for an accurate dosimetry standard. A dosimetry standard for the direct measurement of absolute dose to water in 192Ir sources is not available.The AAPM TG-43, along with its update, constitutes the accepted protocol for dose to water determination based on an air kerma strength Sk,air measurement. The air kerma strength of the radioactive source is converted to dose to water via dose rate constant Λ (a calculated absolute quantify) and several relative correction factors accounting for scatter attenuation and anisotropy of the dose distribution among other effects.In this work, we proposed an absorbed dose conversion by determination of a beam quality factor (kQ) with an ionization chamber. Ideally, the kQ should be measured directly for each chamber at the same quality as the user beam. However, this is not achievable in most standards laboratories. When no experimental data are available, or it is difficult to measure kQ directly to realistic beams, in many cases the correction factors can be calculated theoretically with Monte Carlo method. The geometric design and material details of the source was provided by the manufacturer and was used to define the Monte Carlo geometry. To validate the source geometry, a few dosimetry parameters had to be calculated according to the AAPM TG-43U1 formalism. The dosimetry studies included the calculation of the air kerma strength Sk, collision kerma in water along the transverse axis with an unbounded phantom, dose rate constant and radial dose function. The Monte Carlo code system that was used was EGSnrc with a new cavity code, which is a part of EGS++ that allows calculating the radial dose function around the source. The XCOM photon cross-section library was used in subsequent simulations. Consequently, the photoelectric effect, pair production, Rayleigh scattering and bound Compton scattering were included in the simulation. Variance reduction techniques were also used in the simulations to speed up the calculation. The obtained radial dose function and dose rate constant of the Gammamed Plus 192Ir source in this work were compared with those obtained by Ballester et al. and Taylor &Rogers et al.A value of 1.109 ± 0.003 for the dose to the chamber to dose to water ratio was determined for PTW 30013 ionization chamber. The agreement between the EGSnrc calculated and TRS-398 reported result is encouragingly similar. The beam quality correction factor, kQ, was obtained at 2 cm. This ratio corresponds to the beam quality conversion factor from 60Co to 192Ir. With this kQ it is possible measure the absorbed dose to water at any point for HDR 192Ir source.

Performance evaluation of a direct-conversion flat-panel detector system in imaging and quality assurance for a high-dose-rate 192Ir source

In high-dose-rate (HDR) brachytherapy, a direct-conversion flat-panel detector (d-FPD) clearly depicts a 192Ir source without image halation, even under the emission of high-energy gamma rays. However, it was unknown why iridium is visible when using a d-FPD. The purpose of this study was to clarify the reasons for visibility of the source core based on physical imaging characteristics, including the modulation transfer functions (MTF), noise power spectral (NPS), contrast transfer functions, and linearity of d-FPD to high-energy gamma rays. The acquired data included: x-rays, [X]; gamma rays, [γ]; dual rays (X + γ), [D], and subtracted data for depicting the source ([D] − [γ]). In the quality assurance (QA) test for the positional accuracy of a source core, the coordinates of each dwelling point were compared between the planned and actual source core positions using a CT/MR-compatible ovoid applicator and a Fletcher–Williamson applicator. The profile curves of [X] and ([D] − [γ]) matched well on MTF and NPS. The contrast resolutions of [D] and [X] were equivalent. A strongly positive linear correlation was found between the output data of [γ] and source strength (r2 > 0.99). With regard to the accuracy of the source core position, the largest coordinate difference (3D distance) was noted at the maximum curvature of the CT/MR-compatible ovoid and Fletcher–Williamson applicators, showing 1.74 ± 0.02 mm and 1.01 ± 0.01 mm, respectively. A d-FPD system provides high-quality images of a source, even when high-energy gamma rays are emitted to the detector, and positional accuracy tests with clinical applicators are useful in identifying source positions (source movements) within the applicator for QA.

Mid-Infrared Standoff Spectroscopy Using a Supercontinuum Laser with Compact Fabry–Pérot Filter Spectrometers

Mid-infrared (MIR) supercontinuum (SC) lasers are an attractive new option in the field of IR spectroscopy, especially for standoff detection. Supercontinuum radiation unites high brightness, high spatial coherence, and broadband spectral coverage, thereby surpassing thermal IR sources and challenging quantum cascade lasers. The employed SC source operates in the spectral region of 1.2-4.6 µm, filling the spectral gap where quantum cascade lasers lack broader availability. In this work, the SC radiation was recorded by compact Fabry-Pérot filter spectrometers ideally suited for sensitive standoff detection with real-time capability. The noise performance of the setup and measurements of different substances at standoff distances are presented, e.g., of different paints on a metal surface and an explosive precursor. Furthermore, the real-time capability of the setup is demonstrated by monitoring the evaporation of liquid 2-propanol.