IR Source Research Articles

Markarian survey and Markarian galaxies

Markarian survey (or the First Byurakan Survey, FBS) was the first systematic survey for active galaxies and was a new method for search for such objects. Until now, it is the largest objective prism survey of the sky (17,000 deg2). It was carried out in 1965-1980 by B. E. Markarian and his colleagues and resulted in discovery of 1517 UV-excess (Markarian) galaxies. They contain many active galaxies, as well as powerful gamma-, X-ray, IR and radio sources (Mrk 180, 231, 421, 501, etc.), BCDGs (Mrk 116) and interacting/merging systems (Mrk 266, 273, etc.). They led to the classification of Seyfert galaxies into Sy1 and Sy2 and the definition of Starbursts (SB). Several catalogs of Markarian galaxies have been published (Bicay et al., 1995, Markarian et al., 1989, Mazzarella & Balzano, 1986, Petrosian et al., 2007) and they are accessible in all corresponding databases. Markarian survey also served as a basis for search for UVX stellar objects (including QSOs and Seyferts), late-type stars and optical identification of IR sources. At present the survey is digitized and DFBS database is available. We review the main characteristics of the Markarian survey, its comparison with other similar surveys and the importance of Markarian galaxies in modern astrophysics.

The 2019-2020 EURADOS WG10 and RENEB Field Test of Retrospective Dosimetry Methods in a Small-Scale Incident Involving Ionizing Radiation.

With the use of ionizing radiation comes the risk of accidents and malevolent misuse. When unplanned exposures occur, there are several methods which can be used to retrospectively reconstruct individual radiation exposures; biological methods include analysis of aberrations and damage of chromosomes and DNA, while physical methods rely on luminescence (TL/OSL) or EPR signals. To ensure the quality and dependability of these methods, they should be evaluated under realistic exposure conditions. In 2019, EURADOS Working Group 10 and RENEB organized a field test with the purpose of evaluating retrospective dosimetry methods as carried out in potential real-life exposure scenarios. A 1.36 TBq 192Ir source was used to irradiate anthropomorphic phantoms in different geometries at doses of several Gy in an outdoor open-air geometry. Materials intended for accident dosimetry (including mobile phones and blood) were placed on the phantoms together with reference dosimeters (LiF, NaCl, glass). The objective was to estimate radiation exposures received by individuals as measured using blood and fortuitous materials, and to evaluate these methods by comparing the estimated doses to reference measurements and Monte Carlo simulations. Herein we describe the overall planning, goals, execution and preliminary outcomes of the 2019 field test. Such field tests are essential for the development of new and existing methods. The outputs from this field test include useful experience in terms of planning and execution of future exercises, with respect to time management, radiation protection, and reference dosimetry to be considered to obtain relevant data for analysis.

Development of a low-sensitivity high resolution YAP(Ce) scintillation camera system toward the real-time imaging of an 192Ir source during high-dose-rate brachytherapy

Measurement of the precise position of a high activity iridium-192 (192Ir) source during high-dose-rate (HDR) brachytherapy is desired to detect the mispositioning of the source and avoid incidents. Although real-time imaging of the source position using a high-energy gamma camera is a possible method for this purpose, electronics are saturated at small distances from the source because the 192Ir source activity is so high. To solve this problem, we developed a low-sensitivity high-resolution gamma camera. We used a 1-mm-thick cerium-doped yttrium aluminum perovskite (YA1O3: YAP(Ce)) scintillator plate to reduce sensitivity. The developed low-sensitivity gamma camera consists of this thin YAP(Ce) scintillator optically coupled to a flat panel photomultiplier tube (FP-PMT). It is encased in a 20-mm-thick tungsten shield with a 0.5-mm diameter pinhole collimator mounted on its head. The spatial resolution of the gamma camera at 100 mm from the 192Ir source was 3.3 mm FWHM and the sensitivity was 0.52 cps/MBq. The count rate of the camera was ∼180-k cps at 100 mm from the 212.4-GBq 192Ir source and real-time imaging of the 192Ir source was possible. With a 100-mm-thick water phantom positioned between the gamma camera and the 192Ir source, we decreased the count rate to half, but the 192Ir source images could be observed clearly. We conclude that the developed low-sensitivity high-resolution gamma camera system has the potential to be a new real-time imaging system for HDR brachytherapy.

Monitoring the Fractional Distillation Purification of Inorganic Hydrides by Diode Laser Absorption Spectroscopy

We present our findings on the use of diode laser spectroscopy (DLS) for monitoring СО2, Н2О, СН4, C2H2, C2H4, NH3, and other gas impurities during low-temperature fractional distillation purification of gaseous hydrides. We demonstrate a lineup of instruments and techniques for continuously monitoring impurities during purification of hydrides: NH3, AsH3, РН3, and SiH4. The IR sources used are distributed feedback diode lasers (DLs) having a single mode output fiber pigtail and covering the near-IR spectral region, from 0.7 to 2.0 μm, where overtone and combination absorption bands of the impurities of interest are located. The systems offer high sensitivity and speed in impurity concentration measurements. Owing to their small size and low energy consumption, they can readily be integrated into a process equipment (components of fractionation columns) and enable prolonged continuous monitoring of the purity of hydrides. We describe gas concentration measurement techniques that use conventional high-resolution differential absorption spectroscopy and new, modulation correlation approaches for monitoring a weak molecular absorption by an impurity of interest against a strong selective absorption background of a matrix substance (hydride under study). We present results of technological experiments concerned with the low-temperature fractional distillation of hydrides and the degree of impurity removal from them as monitored by DLS.

Absorbed dose to water standard for 192Ir HDR sources using Fricke Dosimetry

The Fricke solution is a chemical dosimeter that is based on the oxidation of ferrous ions to ferric ions in the solution after interaction with ionizing radiation. It is composed of 96% water (by weight), and its density is thus remarkably similar to that of water. In addition, studies show that the Fricke dosimeter can be used as a primary dosimeter in the determination of the absorbed dose to water for high dose rate (HDR) 192Ir brachytherapy. The Radiological Sciences Laboratory of the University of Rio de Janeiro State (LCR/UERJ) has been investigating the use of the Fricke dosimeter in various applications for more than ten years, particularly in the area of radiotherapy. This review paper presents important improvements in recent years by the LCR/UERJ in the determination of the absorbed dose to water for 192Ir sources. This includes a newly designed irradiation vessel, a new reading device, a description of the need for careful temperature control during irradiation and reading, a more accurate calculation of the correction factors and the results of an intercomparison with the National Calibration Laboratory of Canada. Careful preparation of the Fricke solution is one of the most critical steps in the process. Over the years, the LCR/UERJ has tested different methods of preparing the solution and the final procedure is presented. Regarding the irradiation vessel, a molded double-walled, spherical flask for the Fricke solution was first constructed and used to measure the absorbed dose to water. However, as it was difficult to manipulate the spherical flask, a second design also made with PMMA was molded as a cylinder, with a central tube where the source was centrally positioned. Different methodologies have been reported in the determination of the G-value, a key parameter in Fricke dosimetry, and herein, two different methodologies used by the LCR are reviewed. For the absorbed-dose-to-water determination for 192Ir sources, the overall combined uncertainty associated with the measurements is estimated to be less than 1% for k = 1. Thus, the obtained uncertainties for the determination of the absorbed dose to water using Fricke dosimetry are lower than those obtained using the standard protocols. With respect to clinical practice, this could improve the accuracy in the calculation of the dose delivered to the patients. Overall, the results show that Fricke dosimetry is a reliable system to measure absorbed dose to water as a standard for HDR 192Ir.

End-to-end dosimetric audit: A novel procedure developed for Irish HDR brachytherapy centres.

A dosimetric audit of Ir-192 high dose rate (HDR) brachytherapy remote after-loading units was carried out in 2019. All six brachytherapy departments on the island of Ireland participated in an end-to-end test and in a review of local HDR dosimetry procedures. A 3D-printed customised phantom was created to position the following detectors at known distances from the HDR source: a Farmer ionization chamber, GafChromic film and thermoluminescent dosimeters (TLDs). Dedicated HDR applicator needles were used to position an Ir-192 source at 2cm distance from these detectors. The end-to-end dosimetry audit pathway was performed at each host site and included the stages of imaging, applicator reconstruction, treatment planning and delivery. Deviations between planned and measured dose distributions were quantified using gamma analysis methods. Local procedures were also discussed between auditors and hosts. The mean difference between Reference Air Kerma Rate (RAKR) measured during the audit and RAKR specified by the vendor source certificate was 1.3%. The results of end-to-end tests showed a mean difference between calculated and measured dose of 2.5% with TLDs and less than 0.5% with Farmer chamber measurements. GafChromic films showed a mean gamma passing rates of >95% for plastic and metal applicators with 2%/1 mm global tolerance criteria. The results of this audit indicate dosimetric consistency between centres. The 'end to end' dosimetry audit methodology for HDR brachytherapy has been successfully implemented in a multicentre environment, which included different models of Ir-192 sources and different treatment planning systems. The ability to create a 3D-printed water-equivalent phantom customised to accurately position all three detector types simultaneously at controlled distances from the Ir-192 source under evaluation gives good reproducibility for end-to-end methodology.

Positional and angular tracking of HDR 192 Ir source for brachytherapy quality assurance using radiochromic film dosimetry.

To quantify and verify the dosimetric impact of high-dose rate (HDR) source positional uncertainty in brachytherapy, and to introduce a model for three-dimensional (3D) position tracking of the HDR source based on a two-dimensional (2D) measurement. This model has been utilized for the development of a comprehensive source quality assurance (QA) method using radiochromic film (RCF) dosimetry including assessment of different digitization uncertainties. An algorithm was developed and verified to generate 2D dose maps of the mHDR-V2 192 Ir source (Elekta, Veenendaal, Netherlands) based on the AAPM TG-43 formalism. The limits of the dosimetric error associated with source (0.9mm diameter) positional uncertainty were evaluated and experimentally verified with EBT3 film measurements for 6F (2.0mm diameter) and 4F (1.3mm diameter) size catheters at the surface (4F, 6F) and 10mm further (4F only). To quantify this uncertainty, a source tracking model was developed to incorporate the unique geometric features of all isodose lines (IDLs) within any given 2D dose map away from the source. The tracking model normalized the dose map to its maximum, then quantified the IDLs using blob analysis based on features such as area, perimeter, weighted centroid, elliptic orientation, and circularity. The Pearson correlation coefficients (PCCs) between these features and source coordinates (x, y, z, θy , θz ) were calculated. To experimentally verify the accuracy of the tracking model, EBT3 film pieces were positioned within a Solid Water® (SW) phantom above and below the source and they were exposed simultaneously. The maximum measured dosimetric variations on the 6F and 4F catheter surfaces were 39.8% and 36.1%, respectively. At 10mm further, the variation reduced to 2.6% for the 4F catheter which is in agreement with the calculations. The source center (x, y) was strongly correlated with the low IDL-weighted centroid (PCC=0.99), while the distance to source (z) was correlated with the IDL areas (PCC=0.96) and perimeters (PCC=0.99). The source orientation θy was correlated with the difference between high and low IDL-weighted centroids (PCC=0.98), while θz was correlated with the elliptic orientation of the 60-90% IDLs (PCC=0.97) for a maximum distance of z=5mm. Beyond 5mm, IDL circularity was significant, therefore limiting the determination of θz (PCC≤0.48). The measured positional errors from the film sets above and below the source indicated a source position at the bottom of the catheter (-0.24±0.07mm). Isodose line features of a 2D dose map away from the HDR source can reveal its spatial coordinates. RCF was shown to be a suitable dosimeter for source tracking and dosimetry. This technique offers a novel source QA method and has the potential to be used for QA of commercial and customized applicators.

169 Yb-based rotating shield brachytherapy for prostate cancer.

To present a system for the treatment of prostate cancer in a single-fraction regimen using 169 Yb-based rotating shield brachytherapy (RSBT) with a single-catheter robotic delivery system. The proposed system is innovative because it can deliver RSBT through multiple implanted needles independently, in serial, using flexible catheters, with no inter-needle shielding effects and without the need to rotate multiple shielded catheters inside the needles simultaneously, resulting in a simple, mechanically robust, delivery approach. RSBT was compared to conventional 192 Ir-based high-dose-rate brachytherapy (HDR-BT) in a treatment planning study with dose escalation and urethral sparing goals, representing single-fraction brachytherapy monotherapy and brachytherapy as a boost to external beam radiotherapy, respectively. A prototype mechanical delivery system was constructed and quantitatively evaluated as a proof of concept. Treatment plans for twenty-six patients with single fraction prescriptions of 20.5 and 15Gy, were created for dose escalation and urethral sparing, respectively. The RSBT and HDR-BT delivery systems were modeled with one partially shielded 999GBq (27Ci) 169 Yb source and one 370GBq (10Ci) 192 Ir source, respectively. A prototype angular drive system for helical source delivery was constructed. Mechanical accuracy measurements of source translational position and angular orientation in a simulated treatment delivery setup were obtained using the prototype system. For dose escalation, with equivalent urethra D10% , PTV D90% for RSBT vs HDR-BT increased from 22.6±0.0Gy (average±standard deviation) to 29.3±0.9Gy, or 29.9 %±3.0%, with treatment times of 51.4±6.1min for RSBT and 15.8±2.3min for 10Ci 192 Ir-based HDR-BT. For urethra sparing, with equivalent PTV D90 % , urethra D10% for RSBT vs HDR-BT decreased for RSBT vs HDR-BT from 15.6±0.4Gy to 12.0±0.4Gy, or 23.1% ± 3.5%, with treatment times of 30.0±3.7min for RSBT and 12.3±1.8min for HDR-BT. Differences between measured vs predicted rotating catheter positions (corresponding to source position) were within 0.18mm±0.12mm longitudinally and 0.07° ± 0.78°. 169 Yb-based RSBT can increase PTV D90% or decrease urethral D10% relative to HDR-BT with treatment times of less than 1h using a single-source robotic delivery system with treatment delivered in a single fraction. The prototype helical delivery system was able to demonstrate adequate mechanical accuracy.

Monte Carlo simulation of the effect of magnetic fields on brachytherapy dose distributions in lung tissue material.

The aim of this work was to use TOPAS Monte Carlo simulations to model the effect of magnetic fields on dose distributions in brachytherapy lung treatments, under ideal and clinical conditions. Idealistic studies were modeled consisting of either a monoenergetic electron source of 432 keV, or a polyenergetic electron source using the spectrum of secondary electrons produced by 192Ir gamma-ray irradiation. The electron source was positioned in the center of a homogeneous, lung tissue phantom (ρ = 0.26 g/cm3). Conversely, the clinical study was simulated using the VariSource VS2000 192Ir source in a patient with a lung tumor. Three contoured volumes were considered: the tumor, the planning tumor volume (PTV), and the lung. In all studies, dose distributions were calculated in the presence or absence of a constant magnetic field of 3T. Also, TG-43 parameters were calculated for the VariSource and compared with published data from EGS-brachy (EGSnrc) and PENELOPE. The magnetic field affected the dose distributions in the idealistic studies. For the monoenergetic and poly-energetic studies, the radial distance of the 10% iso-dose line was reduced in the presence of the magnetic field by 64.9% and 24.6%, respectively. For the clinical study, the magnetic field caused differences of 10% on average in the patient dose distributions. Nevertheless, differences in dose-volume histograms were below 2%. Finally, for TG-43 parameters, the dose-rate constant from TOPAS differed by 0.09% ± 0.33% and 0.18% ± 0.33% with respect to EGS-brachy and PENELOPE, respectively. The geometry and anisotropy functions differed within 1.2% ± 1.1%, and within 0.0% ± 0.3%, respectively. The Lorentz forces inside a 3T magnetic resonance machine during 192Ir brachytherapy treatment of the lung are not large enough to affect the tumor dose distributions significantly, as expected. Nevertheless, large local differences were found in the lung tissue. Applications of this effect are therefore limited by the fact that meaningful differences appeared only in regions containing air, which is not abundant inside the human.

Dosimetry of a sonolucent material for an ultrasound-compatible gynecologic high-dose-rate brachytherapy cylinder using Monte Carlo simulation and radiochromic film

Purposehe purpose of this study was to study the dosimetric characterization of sonolucent material “TPX” to be used toward gynecologic high-dose-rate brachytherapy treatments using ultrasound-compatible cylinders in non–model-based dose calculation workflows. MethodsMonte Carlo simulations were performed using EGSnrc application egs_brachy in cylinders of polymethylpentene (TPX) plastic, water, and PMMA. Simulations were performed of five 192Ir sources placed longitudinally in ∼3.7 cm diameter, 5.0 cm length cylinders (matching physical cylinders used in film measurements). TPX and PMMA dose distributions and percentage depth dose curves were compared relative to water.Film measurements were performed to validate egs_brachy simulations. TPX and PMMA cylinders were placed in a water tank using 3D-printed supports to position film radially and touching the surface of the cylinders. The same five 192Ir dwell positions were delivered as simulated in egs_brachy. ResultsThe egs_brachy and film percentage depth doses agreed within film uncertainties. The egs_brachy relative dose difference between TPX and water was (0.74 ± 0.09)% and between PMMA and water was (-0.79 ± 0.09)% over the dose scoring phantom. Dose differences for TPX and PMMA relative to water were less than ± 1% within 5 cm of the cylinder surface. ConclusionsIn a solid sonolucent sheath of TPX, the dosimetric differences are comparable with PMMA and other applicator materials in clinical use. No additional uncertainty to dose calculation is introduced when treating through TPX cylinders compared with current applicator materials, and therefore, it is acceptable to perform gynecologic brachytherapy treatments with a sonolucent sheath inserted during radiation delivery.

Technical Note: Scintillation markers for real-time visual source tracking during skin high dose rate brachytherapy.

Treatment misadministration during high dose rate (HDR) brachytherapy is mainly caused due to gross errors in incorrect manual entry of catheter length and manual connection of hardware. The probability of these errors increases with increasing complexity of a surface applicator. A simple, real-time visual verification method was developed using a scintillator to enhance quality assurance (QA) measures for HDR surface brachytherapy and thus reduce manual errors and improve patient safety. Scintillation markers were fabricated from cerium-doped lutetium yttrium orthosilicate (LYSO) embedded in a polymer compound to form 5-mm diameter markers. To verify catheter-transfer tube connections, markers were attached to each channel of a Freiburg flap and irradiated with an 192 Ir source. To determine if the source reached the edge of a target, markers were placed along the periphery. The HDR source was visually tracked by following the illumination from the markers. The response of the markers was also verified in the presence of thermoplastic material overlaid on the Freiburg applicator. Scintillation markers emitted intense blue visible light upon irradiation when the HDR source was beneath the marker, verifying the source's presence in the correct catheter. The signal was clearly visible even when the marker was placed on top of the thermoplastic material covering the Freiburg Flap. Crosstalk from adjacent catheters was <50% of the maximum light intensity. Scintillation markers and paint were developed to successfully meet the challenge of visually tracking of HDR source during brachytherapy by surface applicators. This direct visualization of source allows real-time catheter verification during treatment, and correct superficial target coverage, thus preventing a medical event. It can easily be integrated into pre-existing QA program.

THE EFFECT OF GOLD NANOPARTICLES ON RADIATION DOSE DISTRIBUTION IN BREAST CANCER USING MONTE CARLO SIMULATION

The simulation model for MCNP5 code was used to study the effect of the gold nanoparticle (AuNPs) in cancer breast samples. The dose rate distribution of AuNPs in water and breast phantom was calculated using MCNP5 code. For inhomogeneities, cone cells were designed to calculate dose distribution around Ir-192 source in breast and inhomogeneous medium that includes gold nanoparticles at different concentration. Both barometers, the track length energy deposition tally (F6) and pulse height tally (*F8), were used. The result indicated that the F6 is better than *F8 for radiation dose calculation. Angular doses distribution in water was compared with data published for tally F6 and*F8 with the different percentage range of 0.0136 to 0.3019% for tally F6 at the average angle of 5˚and 175˚respectively. For *F8 tally, different percentage range of - 0.0014 to 0.8253 % was obtained at an average angle of 75˚and 5˚ respectively. For breast phantom, the result of the F6 tally with the *F8 tally was compared. The difference in calculations between the two tallies in the angular anisotropic distribution was found to be in the range from 0.0514 to 0.4596% at the average angle of 15 ˚ and 175 ˚ respectively. The obtained results showed that the AuNP dose increases when the concentration increases up to ten percent (100 mg/ml), and then decreases for concentration higher than ten percent. The concentration of AuNPs greater than ten percent is not recommended. The results indicated that tally F6 is a good tool to calculate the effect of inhomogeneities due to breast cancer on brachytherapy.

Shielding design for high-intensity Co-60 and Ir-192 gamma sources used in industrial radiography based on PHITS Monte Carlo simulations

Protection in industrial radiography facilities has been a worldwide concern for decades and the most appropriate protection for the public and operators in small scale facilities is the engineering protection including shielding first, time and distance. Monte Carlo methods were used for thickness determination in shielding design for gamma imaging using gamma sources in fixed facilities. Computation was done to develop the concrete design that can slow down the effective dose rate of the gamma rays from 100 Ci (or less) of Co-60 and 50 Ci (or less) of Ir-192 less than the value of 2.5 μSv/h (the limit for Public area) as required by the ALARA principle and regulation of different countries. The minimum concrete wall thickness necessary to achieve the ALARA principle in the previous conditions was found to be 120 cm for Co-60 source and 70 cm for the Ir-192 source. From the optimized design using a single corner maze, it was found that the central source position gives rise to high exposure and should not be used as a source position. Only the left and right positions of the source are preferred depending on the facility’s dimensions. For Co-60 with a maze corridor less than 7 m, the right position of the source is the most appropriate while the left position is preferred for larger dimensions. For Ir-192, the right position if preferred if the corridor length is less than 5 m and the left otherwise. Double-corner maze design was found to be the most appropriate shielding design for gamma radiation with the left and right position of the sources the best for both sources used. The double-corner maze required only 4 m maze length to achieve 2.5 µSv/h or less ALARA principle while single corner design requires 12 m or 14 m for left and right positions, respectively.

The Measurement of the Air-Kerma Rate in Air and a Solid Phantom with Ionization Chambers for a 192Ir HDR Brachytherapy Source.

IntroductionThis study aims to measure the air-kerma rate of 192-Ir-HDR-afterloading source with an ionization chamber in air and a solid cylindrical phantom separately and to compare the dose calibration by the American Association of Physicists in Medicine (AAPM) Task Group TG-43U1 formalism with the Abacus treatment planning system (TPS).Materials and MethodsThe air-kerma rate of 192Ir source was measured by an ionization chamber in air and a solid cylindrical phantom separately. For the interesting point position P (8cm, 90°), the values of the dose were calculated with the TG-43U1 formula and compared with data from the Abacus TPS with single and multiple dwell positions, respectively.ResultsThe air-kerma rate percentage deviations between the detector measurements in air and the source certificate were −1.28%, −0.91%, −0.71%, and 0.33% at the distances of 25cm, 50cm, 75cm, and 100cm, respectively. For the measurement in solid cylindrical phantom, the percent deviation from the air-kerma rate certificate was 1.85%. The percentage deviations of the dose calibration between Abacus TPS and TG-43U1 formalism at P (8cm, 90°) were −2.30%, 1.76%, and 2.10% with different distances (between the dwell positions) of 0cm, 0.5cm, and 1cm, respectively.ConclusionThe in-air technique was a new attempt for clinic routine measurement. Further studies are still necessary. As a treatment planning system, the Abacus TPS should apply the AAPM TG-43U1 formulism for the development required in the future.

Infrared Light Absorbance: a New Method for Temperature Compensation in Nondispersive Infrared CO2 Gas Sensor

Nondispersive infrared CO2 gas sensor was developed after the simulation of optical cavity structure and assembling the optical components: IR source, concave reflectors, Fresnel lens, a hollow disk, and IR detectors. By placing a hollow disk in front of reference IR detector, the output voltages are almost constant value, near to 70.2 mV. The absorbance of IR light, Fa, shows the second order of polynomial according to ambient temperatures at 1,500 ppm. The differential output voltages and the absorbance of IR light give a higher accuracy in estimations of CO2 concentrations with less than ± 1.5 % errors. After implementing the parameters that are dependent upon the ambient temperatures in microcontroller unit (MCU), the measured CO2 concentrations show high accuracies (less than ± 1.0 %) from 281 K to 308 K and the time constant of developed sensor is about 58 sec at 301 K. Even though the estimation errors are relatively high at low concentration, the developed sensor is competitive to the commercial product with a high accuracy and the stability.

HDR brachytherapy well chamber calibration and stability evaluated over twenty years of clinical use

PurposeThe purpose of the study was to establish, using a retrospective analysis of existing hospital records, the long-term stability and accuracy of a high-dose-rate brachytherapy well chamber. This should be assessed to determine reliability and appropriate calibration frequency. The accrual of long-term data that demonstrates the stability of our chamber may inform others of the performance they might expect from similar equipment. Methods and MaterialsWe evaluated air kerma strength measurements made with the PTW 32002 (Nucletron 077.091) high-dose-rate well chamber on 72 192Ir sources over an 18-year period and the seven calibrations of that chamber which span a 27-year period. ResultsConsecutive air kerma strength measurements agreed within 0.01% on average. The chamber measurement agreed with the source specification within 0.02% on average, but was up to 1.4% during some calibration periods. The chamber calibration coefficient varied by a maximum of 5% over seven chamber calibration measurements. ConclusionsThe constancy of the well chamber current compared with the source manufacturer suggests that our chamber has been stable to better than 2% over a period of 18 years. Although the chamber has received different calibration coefficients over time, these coefficients are within the combined uncertainties of any two calibrations and are consistent with the chamber being stable. The agreement we have observed between clinical measurements and the source manufacturer would justify an action level for further investigation of 1%, for this specific chamber.

A PRELIMINARY STUDY OF RADIATION QUALITY CORRECTION FACTOR (KQ) DETERMINATION FOR WELL-TYPE IONIZATION CHAMBER

This paper deals with the determination of the radiation quality correction factor (kQ) well-type ionization chamber for the measurement of Co-60 brachytherapy. The measurement of the brachytherapy source has been done in the hospital brachytherapy facilities. The measurement of air Kerma has been done using three different ionization chambers 0.6 cm3, 30 cm3, 80 cm3, which have calibration factor traceability for Co-60 and one well-type ionization chamber which calibrated for Ir-192. The determination of the radiation quality correction factor (kQ) was determined based on the results of the air Kerma ratio between measurements using ionization chambers, which have traceability to Co-60 and Ir-192 sources. The results of the measurement of the reference air Kerma rate (RAKR) obtained from the three chambers were 21.36, 19.87, 19.34 mGy.m2.h-1, while the results of measurements with ionization chambers get a value of 19.01 mGy.m2.h-1. The kQCal results from 0.6 cm3 ionization chamber get a value of 1.07. The kQCal value was compared with the value of Andreas Schuller’s et al. kQreff of 1.05 and get a deviation of 2.2%. Implementation of the booth kQ value on the results of the RAKR from the HDR1000Plus well-type ionization chamber in the measurement of brachytherapy in two different facilities gets maximal deviation 1.7% with dose value from Treatment Planning System (TPS). The deviation was in the acceptable range of ±5%. Based on this, the use of radiation quality correction factor (kQ) value can be implemented as one method if it does not have the traceability factor calibration of the Co-60 brachytherapy source.

The Lung and Soft Tissue Stopping Power Estimates for a Modified Phantom Using MCNPX

The Adult Male® and Adult Female® phantoms of ORNL were modified with Ir-192 source and additional tally cards from the MCNP® data library. The lung and eleven soft tissues were used for the study. The soft tissues include Liver, Stomach, Ovaries, Testes, Brain, Thyroid, Kidney, Pancreas, Gall Bladder, Heart, and the Small Intestine. The computational simulation was achieved using MCNPX with nps of 107 , and the data set of the lung and soft tissues derived for Malaysian population [14]. The relative error, R was &lt;0.05 for F4 and the F6 tallies across the energy range studied. The results obtained for 0.1-10.0 MeV energies for the F4 and F6 tallies were used to estimate the mass stopping power, S/ρ (MeVg1 cm2 ) and the linear stopping power, S (MeV/cm). The result compares favorably among the tissues. This result is very relevant and useful in validating an on-going lung and soft tissue model construction

Verification of dose distribution in high-dose-rate brachytherapy using a nanoclay-based radio-fluorogenic gel dosimeter

Dose distributions have become more complex with the introduction of image-guided brachytherapy in high-dose-rate (HDR) brachytherapy treatments. Therefore, to correctly execute HDR, conducting a quality assurance programme for the remote after-loading system and verifying the dose distribution in the patient treatment plan are necessary. The characteristics of the dose distribution of HDR brachytherapy are that the dose is high near the source and rapidly drops when the distance from the source increases. Therefore, a measurement tool corresponding to the characteristic is required. In this study, using an Iridium-192 (Ir-192) source, we evaluated the basic characteristics of a nanoclay-based radio-fluorogenic gel (NC-RFG) dosimeter that is a fluorescent gel dosimeter using dihydrorhodamine 123 hydrochloride as a fluorescent probe. The two-dimensional dose distribution measurements were performed at multiple source positions to simulate a clinical plan. Fluorescence images of the irradiated NC-RFG were obtained at a high resolution (0.04 mm pixel–1) using a gel scanner with excitation at 465 nm. Good linearity was confirmed up to a dose range of 100 Gy without dose rate dependence. The dose distribution measurement at the five-point source position showed good agreement with the treatment planning system calculation. The pass ratio by gamma analysis was 92.1% with a 2%/1 mm criterion. The NC-RFG dosimeter demonstrates to have the potential of being a useful tool for quality assurance of the dose distribution delivered by HDR brachytherapy. Moreover, compared with conventional gel dosimeters such as polymer gel and Fricke gel dosimeters it solves the problems of diffusion, dose rate dependence and inhibition of oxygen-induced reactions. Furthermore, it facilitates dose data to be read in a short time after irradiation, which is useful for clinical use.

Material characterization of polyamide 12 and related agents used in the multi-jet fusion process: complementary application of high-resolution mass spectrometry and other advanced instrumental techniques

The powder bed-based 3D printing process called multi-jet fusion from HP is used in various industries for different applications. A polymer powder, the so-called fusing and detailing agents, and an IR source are needed. These novel materials offer some challenges for analytical characterization. High-resolution mass spectrometry in combination with a data base search was used as a tool for comprehensive characterization of the agents, the methanol extract of new polyamide 12 powder, and the methanol extract of a grinded 3D printed part. In addition, thermogravimetric studies were carried out. Besides biocides and substances containing ethoxy units, 2-pyrrolidone and triethylene glycol were identified as organic solvents in the agents. The detailing agent contained 3.7% of 2-pyrrolidone and 11.1% of triethylene glycol. The fusing agent contained 18.7% of 2-pyrrolidone and 8.4% of triethylene glycol. Based on the agents’ different functionalities, the water content of the detailing agent was 18% higher as compared to the fusing agent. In addition, the fusing agent contained a carbon black amount of 5.2%. The methanol extract of new polyamide 12 powder contained remaining monomer and oligomer compounds, as well as the oxidation stabilizer Irganox 1098. In the methanol extract of the grinded 3D printed part the cyclic and linear monomer, oligomers, and oxidation stabilizer were found. Moreover, ingredients of the agents were detected. Residues of 2-pyrrolidone, triethylene glycol, 3-benzisothiazolinone, and substances containing ethoxy units were identified in the methanol extract of the grinded 3D printed part. In contrast, no 2-methyl-4-isothiazolin-3-one was observed.Graphical abstract