Search NASA⌕ Search

SEARCH · Search NASA

Results for “IRIDIUM 192”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Real-Time Verification of a High-Dose-Rate Iridium 192 Source Position Using a Modified C-Arm Fluoroscope

Purpose: High-dose-rate (HDR) brachytherapy misdeliveries can occur at any institution, and they can cause disastrous results. Even a patient's death has been reported. Misdeliveries could be avoided with real-time verification methods. In 1996, we developed a modified C-arm fluoroscopic verification of an HDR Iridium 192 source position prevent these misdeliveries. This method provided excellent image quality sufficient to detect errors, and it has been in clinical use at our institutions for 20 years. The purpose of the current study is to introduce the mechanisms and validity of our straightforward C-arm fluoroscopic verification method. Methods and Materials: Conventional X-ray fluoroscopic images are degraded by spurious signals and quantum noise from Iridium 192 photons, which make source verification impractical. To improve image quality, we quadrupled the C-arm fluoroscopic X-ray dose per pulse. The pulse rate was reduced by a factor of 4 to keep the average exposure compliant with Japanese medical regulations. The images were then displayed with quarter-frame rates. Results: Sufficient quality was obtained to enable observation of the source position relative to both the applicators and the anatomy. With this method, 2 errors were detected among 2031 treatment sessions for 370 patients within a 6-year period. Conclusions: With the use of a modified C-arm fluoroscopic verification method, treatment errors that were otherwise overlooked were detected in real time. This method should be given consideration for widespread use.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Using LiF:Mg,Cu,P TLDs to estimate the absorbed dose to water in liquid water around an {sup 192}Ir brachytherapy source

Purpose: The absorbed dose to water is the fundamental reference quantity for brachytherapy treatment planning systems and thermoluminescence dosimeters (TLDs) have been recognized as the most validated detectors for measurement of such a dosimetric descriptor. The detector response in a wide energy spectrum as that of an{sup 192}Ir brachytherapy source as well as the specific measurement medium which surrounds the TLD need to be accounted for when estimating the absorbed dose. This paper develops a methodology based on highly sensitive LiF:Mg,Cu,P TLDs to directly estimate the absorbed dose to water in liquid water around a high dose rate {sup 192}Ir brachytherapy source. Methods: Different experimental designs in liquid water and air were constructed to study the response of LiF:Mg,Cu,P TLDs when irradiated in several standard photon beams of the LNE-LNHB (French national metrology laboratory for ionizing radiation). Measurement strategies and Monte Carlo techniques were developed to calibrate the LiF:Mg,Cu,P detectors in the energy interval characteristic of that found when TLDs are immersed in water around an{sup 192}Ir source. Finally, an experimental system was designed to irradiate TLDs at different angles between 1 and 11 cm away from an {sup 192}Ir source in liquid water. Monte Carlo simulations were performed to correct measured results to provide estimates of the absorbed dose to water in water around the {sup 192}Ir source. Results: The dose response dependence of LiF:Mg,Cu,P TLDs with the linear energy transfer of secondary electrons followed the same variations as those of published results. The calibration strategy which used TLDs in air exposed to a standard N-250 ISO x-ray beam and TLDs in water irradiated with a standard{sup 137}Cs beam provided an estimated mean uncertainty of 2.8% (k = 1) in the TLD calibration coefficient for irradiations by the {sup 192}Ir source in water. The 3D TLD measurements performed in liquid water were obtained with a maximum uncertainty of 11% (k = 1) found at 1 cm from the source. Radial dose values in water were compared against published results of the American Association of Physicists in Medicine and the European Society for Radiotherapy and Oncology and no significant differences (maximum value of 3.1%) were found within uncertainties except for one position at 9 cm (5.8%). At this location the background contribution relative to the TLD signal is relatively small and an unexpected experimental fluctuation in the background estimate may have caused such a large discrepancy. Conclusions: This paper shows that reliable measurements with TLDs in complex energy spectra require a study of the detector dose response with the radiation quality and specific calibration methodologies which model accurately the experimental conditions where the detectors will be used. The authors have developed and studied a method with highly sensitive TLDs and contributed to its validation by comparison with results from the literature. This methodology can be used to provide direct estimates of the absorbed dose rate in water for irradiations with HDR{sup 192}Ir brachytherapy sources.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Limitations of the TG-43 formalism for skin high-dose-rate brachytherapy dose calculations

Purpose: In skin high-dose-rate (HDR) brachytherapy, sources are located outside, in contact with, or implanted at some depth below the skin surface. Most treatment planning systems use the TG-43 formalism, which is based on single-source dose superposition within an infinite water medium without accounting for the true geometry in which conditions for scattered radiation are altered by the presence of air. The purpose of this study is to evaluate the dosimetric limitations of the TG-43 formalism in HDR skin brachytherapy and the potential clinical impact. Methods: Dose rate distributions of typical configurations used in skin brachytherapy were obtained: a 5 cm × 5 cm superficial mould; a source inside a catheter located at the skin surface with and without backscatter bolus; and a typical interstitial implant consisting of an HDR source in a catheter located at a depth of 0.5 cm. Commercially available HDR{sup 60}Co and {sup 192}Ir sources and a hypothetical {sup 169}Yb source were considered. The Geant4 Monte Carlo radiation transport code was used to estimate dose rate distributions for the configurations considered. These results were then compared to those obtained with the TG-43 dose calculation formalism. In particular, the influence of adding bolus material over the implant was studied. Results: For a 5 cm × 5 cm{sup 192}Ir superficial mould and 0.5 cm prescription depth, dose differences in comparison to the TG-43 method were about −3%. When the source was positioned at the skin surface, dose differences were smaller than −1% for {sup 60}Co and {sup 192}Ir, yet −3% for {sup 169}Yb. For the interstitial implant, dose differences at the skin surface were −7% for {sup 60}Co, −0.6% for {sup 192}Ir, and −2.5% for {sup 169}Yb. Conclusions: This study indicates the following: (i) for the superficial mould, no bolus is needed; (ii) when the source is in contact with the skin surface, no bolus is needed for either {sup 60}Co and {sup 192}Ir. For lower energy radionuclides like {sup 169}Yb, bolus may be needed; and (iii) for the interstitial case, at least a 0.1 cm bolus is advised for {sup 60}Co to avoid underdosing superficial target layers. For {sup 192}Ir and {sup 169}Yb, no bolus is needed. For those cases where no bolus is needed, its use might be detrimental as the lack of radiation scatter may be beneficial to the patient, although the 2% tolerance for dose calculation accuracy recommended in the AAPM TG-56 report is not fulfilled.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part II. High dose rate {sup 192}Ir sources

Purpose: Historically, treatment of malignant surface lesions has been achieved with linear accelerator based electron beams or superficial x-ray beams. Recent developments in the field of brachytherapy now allow for the treatment of surface lesions with specialized conical applicators placed directly on the lesion. Applicators are available for use with high dose rate (HDR){sup 192}Ir sources, as well as electronic brachytherapy sources. Part I of this paper discussed the applicators used with electronic brachytherapy sources. Part II will discuss those used with HDR {sup 192}Ir sources. Although the use of these applicators has gained in popularity, the dosimetric characteristics have not been independently verified. Additionally, there is no recognized method of output verification for quality assurance procedures with applicators like these. Methods: This work aims to create a cohesive method of output verification that can be used to determine the dose at the treatment surface as part of a quality assurance/commissioning process for surface applicators used with HDR electronic brachytherapy sources (Part I) and{sup 192}Ir sources (Part II). Air-kerma rate measurements for the {sup 192}Ir sources were completed with several models of small-volume ionization chambers to obtain an air-kerma rate at the treatment surface for each applicator. Correction factors were calculated using MCNP5 and EGSnrc Monte Carlo codes in order to determine an applicator-specific absorbed dose to water at the treatment surface from the measured air-kerma rate. Additionally, relative dose measurements of the surface dose distributions and characteristic depth dose curves were completed in-phantom. Results: Theoretical dose distributions and depth dose curves were generated for each applicator and agreed well with the measured values. A method of output verification was created that allows users to determine the applicator-specific dose to water at the treatment surface based on a measured air-kerma rate. Conclusions: The novel output verification methods described in this work will reduce uncertainties in dose delivery for treatments with these kinds of surface applicators, ultimately improving patient care.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part I. Electronic brachytherapy source

Purpose: Historically, treatment of malignant surface lesions has been achieved with linear accelerator based electron beams or superficial x-ray beams. Recent developments in the field of brachytherapy now allow for the treatment of surface lesions with specialized conical applicators placed directly on the lesion. Applicators are available for use with high dose rate (HDR){sup 192}Ir sources, as well as electronic brachytherapy sources. Part I of this paper will discuss the applicators used with electronic brachytherapy sources; Part II will discuss those used with HDR {sup 192}Ir sources. Although the use of these applicators has gained in popularity, the dosimetric characteristics including depth dose and surface dose distributions have not been independently verified. Additionally, there is no recognized method of output verification for quality assurance procedures with applicators like these. Existing dosimetry protocols available from the AAPM bookend the cross-over characteristics of a traditional brachytherapy source (as described by Task Group 43) being implemented as a low-energy superficial x-ray beam (as described by Task Group 61) as observed with the surface applicators of interest. Methods: This work aims to create a cohesive method of output verification that can be used to determine the dose at the treatment surface as part of a quality assurance/commissioning process for surface applicators used with HDR electronic brachytherapy sources (Part I) and{sup 192}Ir sources (Part II). Air-kerma rate measurements for the electronic brachytherapy sources were completed with an Attix Free-Air Chamber, as well as several models of small-volume ionization chambers to obtain an air-kerma rate at the treatment surface for each applicator. Correction factors were calculated using MCNP5 and EGSnrc Monte Carlo codes in order to determine an applicator-specific absorbed dose to water at the treatment surface from the measured air-kerma rate. Additionally, relative dose measurements of the surface dose distributions and characteristic depth dose curves were completed in-phantom. Results: Theoretical dose distributions and depth dose curves were generated for each applicator and agreed well with the measured values. A method of output verification was created that allows users to determine the applicator-specific dose to water at the treatment surface based on a measured air-kerma rate. Conclusions: The novel output verification methods described in this work will reduce uncertainties in dose delivery for treatments with these kinds of surface applicators, ultimately improving patient care.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

SU-F-P-24: Radiological Disperse Device

Purpose: We are now living in a society of constant fear of terrorism. This topic is pertaining to give a general knowledge of what is a radiological dispersion device or RDD and in case of its detonation, what are the options open to public for a safe action in terms of reducing the exposure and knowing the proper steps. These RDD are also called dirty bombs. Methods: Compared to nuclear weapons, dirty bombs are easy to make. In order for a terrorist organization to construct and detonate a dirty bomb, it must acquire radioactive material by stealing it or buying it through legal or illegal channels. Possible RDD material could come from the millions of radioactive sources used in the industry, for medical purposes and in academic applications mainly for researches. These are, americium-{sup 241}, californium-{sup 252}, caesium-{sup 137}, cobalt-{sup 60}, iridium-{sup 192}, plutonium-{sup 238}, polonium-{sup 210}, radium-{sup 226} and strontium-{sup 90}. Results: Prompt detection of the type of radioactive material used will greatly assist advising people on the protective measures, like sheltering in place, or quickly leaving the immediate area. The effects of radiation are determined by:°the amount of radiation absorbed by body°the type of radiation °the distance from the radiation to an individual°the means of exposure absorbed by the skin, inhaled, or ingested; and length of time exposed. Conclusion: In any facility it is now much more important to keep a log list of all radioactive materials in use. In case there is a dirty bomb explosion, the chaos and economic cost could be enormous. The economic cost for the evaluation of the contamination, survey of people and surroundings and the after treatment, decontamination cost and effort will be a big challenge in any country. So awareness and preparation is the start to face this new type of challenge.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2013

Qualification tests for {sup 192}Ir sealed sources

This paper describes the results of qualification tests for {sup 192}Ir sealed sources, available in Testing and Nuclear Expertise Laboratory of National Institute for Physics and Nuclear Engineering 'Horia Hulubei' (I.F.I.N.-HH), Romania. These sources had to be produced in I.F.I.N.-HH and were tested in order to obtain the authorization from The National Commission for Nuclear Activities Control (CNCAN). The sources are used for gammagraphy procedures or in gammadefectoscopy equipments. Tests, measurement methods and equipments used, comply with CNCAN, AIEA and International Quality Standards and regulations. The qualification tests are: 1. Radiological tests and measurements: dose equivalent rate at 1 m; tightness; dose equivalent rate at the surface of the transport and storage container; external unfixed contamination of the container surface. 2. Mechanical and climatic tests: thermal shock; external pressure; mechanic shock; vibrations; boring; thermal conditions for storage and transportation. Passing all tests, it was obtained the Radiological Security Authorization for producing the {sup 192}Ir sealed sources. Now IFIN-HH can meet many demands for this sealed sources, as the only manufacturer in Romania.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

Impact of an external radiation field on handheld XRF measurements for nuclear forensics applications

X-ray fluorescence (XRF) is an attractive technique for nuclear forensics applications. We evaluated a handheld, portable XRF device by applying an external radiation field (10 mR/h to 17 R/h) using two types of radiography sources: a 60 Co radiography camera to observe effects from high-energy gamma emissions and an 192 Ir radiography camera to observe effects from several low-energy gamma (0.604, 0.468, and 0.317 MeV) and decay daughter x-ray emissions. External radiation tests proved that radiation, in general, has a significant effect on the dead time or background at dose rates over 1 R/hr for both the 192 Ir and 60 Co sources.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

SU-F-T-15: Evaluation of 192Ir, 60Co and 169Yb Sources for High Dose Rate Prostate Brachytherapy Inverse Planning Using An Interior Point Constraint Generation Algorithm

Purpose: The effectiveness of using a combination of three sources, {sup 60}Co, {sup 192}Ir and {sup 169}Yb, is analyzed. Different combinations are compared against a single {sup 192}Ir source on prostate cancer cases. A novel inverse planning interior point algorithm is developed in-house to generate the treatment plans. Methods: Thirteen prostate cancer patients are separated into two groups: Group A includes eight patients with the prostate as target volume, while group B consists of four patients with a boost nodule inside the prostate that is assigned 150% of the prescription dose. The mean target volume is 35.7±9.3cc and 30.6±8.5cc for groups A and B, respectively. All patients are treated with each source individually, then with paired sources, and finally with all three sources. To compare the results, boost volume V150 and D90, urethra Dmax and D10, and rectum Dmax and V80 are evaluated. For fair comparison, all plans are normalized to a uniform V100=100. Results: Overall, double- and triple-source plans were better than single-source plans. The triple-source plans resulted in an average decrease of 21.7% and 1.5% in urethra Dmax and D10, respectively, and 8.0% and 0.8% in rectum Dmax and V80, respectively, for group A. For group B, boost volume V150 and D90 increased by 4.7% and 3.0%, respectively, while keeping similar dose delivered to the urethra and rectum. {sup 60}Co and {sup 192}Ir produced better plans than their counterparts in the double-source category, whereas {sup 60}Co produced more favorable results than the remaining individual sources. Conclusion: This study demonstrates the potential advantage of using a combination of two or three sources, reflected in dose reduction to organs-at-risk and more conformal dose to the target. three sources, reflected in dose reduction to organs-at-risk and more conformal dose to the target. Our results show that {sup 60}Co, {sup 192}Ir and {sup 169}Yb produce the best plans when used simultaneously and can thus be an alternative to {sup 192}Ir-only in high-dose-rate prostate brachytherapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-F-BRA-05: Utility of the Combined Use of Two Types of HDR Sources with the Direction Modulation Brachytherapy (DMBT) Tandem Applicator for Cervical Cancer Treatment

Purpose: To maximize the dose to HRCTV while minimizing dose to the OARs, the combination of two HDR brachytherapy sources, 192-Ir and 169-Yb, used in combination with the recently-proposed novel direction modulated brachytherapy (DMBT) tandem applicator were examined. Methods: The DMBT tandem, made from nonmagnetic tungsten-alloy rod, with diameter of 5.4mm, has 6 symmetric peripheral holes of 1.3mm diameter. The 0.3mm thick bio-compatible plastic tubing wraps the tandem. MCNPX v.2.6 was used to simulate the mHDR 192-Ir V2 and 4140 HDR 169-Yb sources inside the DMBT applicator. Thought was by combining the higher energy 192-Ir (380keV) and lower energy 169-Yb (92.7keV) sources could create unprecedented level of dose conformality when combined with the high-degree intensity modulation capable DMBT tandem applicator. 3D dose matrices, with 1 mm3 resolution, were imported into an in-house-coded inverse optimization planning system to evaluate plan quality of 19 clinical patient cases. Prescription dose was 15Gy. All plans were normalized to receive the same HRCTV D90. Results: Generally, the use of dual sources produced better plans than using either of the sources alone, with significantly better performance in some patients. The mean D2cc for bladder, rectum, and sigmoid were 11.65±2.30Gy, 7.47±3.05Gy, and 9.84±2.48Gy for 192-Ir-only, respectively. For 169 -Yb-only, they were 11.67±2.26Gy, 7.44±3.02Gy, and 9.83±2.38Gy, respectively. The corresponding data for the dual sources were 11.51±2.24Gy, 7.30±3.00Gy, and 9.68 ±2.39Gy, respectively. The HRCTV D98 and V100 were 16.37±1.86Gy and 97.37±1.92Gy for Ir-192-only, respectively. For 169-Yb-only, they were 16.43±1.86Gy, and 97.51±1.91Gy, respectively. For the dual source, they were 16.42±1.87Gy and 97.47±1.93Gy, respectively. Conclusion: The plan quality improves, in some cases quite significantly, for when dual 192-Ir and 169-Yb sources are used in combination with highly intensity modulation capable DMBT tandem applicator for image guided cervical cancer brachytherapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-787: Utility of the Two Candidate 192-Ir and 169-Yb HDR Sources for Use with a Novel Direction Modulated Brachytherapy Tandem Applicator for Cervical Cancer Treatment

Purpose: A novel tungsten alloy shielded, MRI-compatible, direction modulated brachytherapy (DMBT) concept tandem applicator, which enables unprecedented intensity modulation, was used to evaluate treatment plan quality improvement over a conventional tandem. The utility of the 192-Ir and 169-Yb HDR sources, for use with the DMBT applicator, was evaluated. Methods: The total diameter of the DMBT tandem applicator is 6.0 mm, which consists of 5.4-mm diameter tungsten alloy and 0.3 mm thick plastic sheath. The tandem has 6 symmetric peripheral 1.3-mm diameter grooves for the source to travel. MCNPX v.2.6 was used to simulate the 192-Ir and 169-Yb sources inside the DMBT applicator. First, TG-43 source parameters were evaluated. Second, 3D dose matrix with 1 mm3 resolution were imported into an in-house-coded inverse optimization treatment planning program to obtain optimal plans for 19 clinical cases. All plans were compared with the standard tandem and ring plans. Prescription dose was 15.0 Gy. All plans were normalized to receive the same HRCTV D90. Results: Generally, the DMBT tandem (and ring) plans were better than the conventional tandem and ring plans for 192-Ir and 169-Yb HDR sources. The mean data of D2cc for bladder, rectum, and sigmoid were 11.65±2.30 Gy, 7.47±3.05 Gy, and 9.84±2.48 Gy for Ir-192 DMBT tandem, respectively. These data for Yb-169 were 11.67±2.26 Gy, 7.44±3.02 Gy, and 9.83±2.38 Gy, respectively. The HR-CTV D98 and V100 were 16.37±1.86 Gy and 97.37 ± 1.92 Gy for Ir-192 DMBT, respectively. The corresponding values for Yb-169 were 16.43±1.86 Gy, and 97.51 ± 1.91 Gy. Plans with the 169-Yb source generally produced more favorable results where V100 increased by 13.65% while D2cc across all OARs reduced by 0.54% compared with the 192-Ir plans. Conclusion: For the DMBT tandem applicator, 169-Yb source seems to produce more directional beams resulting in increased intensity modulation capacity, thus resulting in more conformal plans.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-102: Determination of Dose Distributions and Water-Equivalence of MAGIC-F Polymer Gel for 60Co and 192Ir Brachytherapy Sources

Purpose: Analyse the water-equivalence of MAGIC-f polymer gel for {sup 60}Co and {sup 192}Ir clinical brachytherapy sources, through dose distributions simulated with PENELOPE Monte Carlo code. Methods: The real geometry of {sup 60} (BEBIG, modelo Co0.A86) and {sup 192}192Ir (Varian, model GammaMed Plus) clinical brachytherapy sources were modelled on PENELOPE Monte Carlo simulation code. The most probable emission lines of photons were used for both sources: 17 emission lines for {sup 192}Ir and 12 lines for {sup 60}. The dose distributions were obtained in a cubic water or gel homogeneous phantom (30 × 30 × 30 cm{sup 3}), with the source positioned in the middle of the phantom. In all cases the number of simulation showers remained constant at 10{sup 9} particles. A specific material for gel was constructed in PENELOPE using weight fraction components of MAGIC-f: wH = 0,1062, wC = 0,0751, wN = 0,0139, wO = 0,8021, wS = 2,58×10{sup −6} e wCu = 5,08 × 10{sup −6}. The voxel size in the dose distributions was 0.6 mm. Dose distribution maps on the longitudinal and radial direction through the centre of the source were used to analyse the water-equivalence of MAGIC-f. Results: For the {sup 60} source, the maximum diferences in relative doses obtained in the gel and water were 0,65% and 1,90%, for radial and longitudinal direction, respectively. For {sup 192}Ir, the maximum difereces in relative doses were 0,30% and 1,05%, for radial and longitudinal direction, respectively. The materials equivalence can also be verified through the effective atomic number and density of each material: Zef-MAGIC-f = 7,07 e .MAGIC-f = 1,060 g/cm{sup 3} and Zef-water = 7,22. Conclusion: The results showed that MAGIC-f is water equivalent, consequently being suitable to simulate soft tissue, for Cobalt and Iridium energies. Hence, gel can be used as a dosimeter in clinical applications. Further investigation to its use in a clinical protocol is needed.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

SU-F-T-33: Air-Kerma Strength and Dose Rate Constant by the Full Monte Carlo Simulations

Purpose: In general, the air-kerma strength (Sk) has been determined by the energy weighting the photon energy fluence and the corresponding mass-energy absorption coefficient or mass-energy transfer coefficient. Kerma is an acronym for kinetic energy released per unit mass, defined as the sum of the initial kinetic energies of all the charged particles. Monte Carlo (MC) simulations can investigate the kinetic energy of the charged particles after photo interactions and sum the energy. The Sk of {sup 192}Ir source is obtained in the full MC simulation and finally the dose rate constant Λ is determine. Methods: MC simulations were performed using EGS5 with the microSelectron HDR v2 type of {sup 192}Ir source. The air-kerma rate obtained to sum the electron kinetic energy after photoelectric absorption or Compton scattering for transverse-axis distance from 1 to 120 cm with a 10 m diameter air phantom. Absorbed dose in water is simulated with a 30 cm diameter water phantom. The transport cut-off energy is 10 keV and primary photons from the source need two hundred and forty billion in the air-kerma rate and thirty billion in absorbed dose in water. Results: Sk is multiplied by the square of the distance in air-kerma rate and determined by fitting a linear function. The result of Sk is (2.7039±0.0085)*10-{sup −11} µGy m{sup 2} Bq{sup −1} s{sup −1}. Absorbed dose rate in water at 1 cm transverse-axis distance D(r{sub 0}, θ{sub 0}) is (3.0114±0.0015)*10{sup −11} cGy Bq{sup −1} s{sup −1}. Conclusion: From the results, dose rate constant Λ of the microSelectron HDR v2 type of {sup 192}Ir source is (1.1137±0.0035) cGy h{sup −1} U{sup −1} by the full MC simulations. The consensus value conΛ is (1.109±0.012) cGy h{sup −1} U{sup −1}. The result value is consistent with the consensus data conΛ.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Development and implementation of a remote audit tool for high dose rate (HDR) Ir-192 brachytherapy using optically stimulated luminescence dosimetry

Purpose: The aim of this work was to create a mailable phantom with measurement accuracy suitable for Radiological Physics Center (RPC) audits of high dose-rate (HDR) brachytherapy sources at institutions participating in National Cancer Institute-funded cooperative clinical trials. Optically stimulated luminescence dosimeters (OSLDs) were chosen as the dosimeter to be used with the phantom.Methods: The authors designed and built an 8 × 8 × 10 cm{sup 3} prototype phantom that had two slots capable of holding Al{sub 2}O{sub 3}:C OSLDs (nanoDots; Landauer, Glenwood, IL) and a single channel capable of accepting all {sup 192}Ir HDR brachytherapy sources in current clinical use in the United States. The authors irradiated the phantom with Nucletron and Varian {sup 192}Ir HDR sources in order to determine correction factors for linearity with dose and the combined effects of irradiation energy and phantom characteristics. The phantom was then sent to eight institutions which volunteered to perform trial remote audits.Results: The linearity correction factor was k{sub L}= (−9.43 × 10{sup −5}× dose) + 1.009, where dose is in cGy, which differed from that determined by the RPC for the same batch of dosimeters using {sup 60}Co irradiation. Separate block correction factors were determined for current versions of both Nucletron and Varian {sup 192}Ir HDR sources and these vendor-specific correction factors differed by almost 2.6%. For the Nucletron source, the correction factor was 1.026 [95% confidence interval (CI) = 1.023–1.028], and for the Varian source, it was 1.000 (95% CI = 0.995–1.005). Variations in lateral source positioning up to 0.8 mm and distal/proximal source positioning up to 10 mm had minimal effect on dose measurement accuracy. The overall dose measurement uncertainty of the system was estimated to be 2.4% and 2.5% for the Nucletron and Varian sources, respectively (95% CI). This uncertainty was sufficient to establish a ±5% acceptance criterion for source strength audits under a formal RPC audit program. Trial audits of four Nucletron sources and four Varian sources revealed an average RPC-to-institution dose ratio of 1.000 (standard deviation = 0.011).Conclusions: The authors have created an OSLD-based {sup 192}Ir HDR brachytherapy source remote audit tool which offers sufficient dose measurement accuracy to allow the RPC to establish a remote audit program with a ±5% acceptance criterion. The feasibility of the system has been demonstrated with eight trial audits to date.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2015

A radiation quality correction factor k{sub Q} for well-type ionization chambers for the measurement of the reference air kerma rate of {sup 60}Co HDR brachytherapy sources

Purpose: The aim of this study was to investigate whether a chamber-type-specific radiation quality correction factor k{sub Q} can be determined in order to measure the reference air kerma rate of {sup 60}Co high-dose-rate (HDR) brachytherapy sources with acceptable uncertainty by means of a well-type ionization chamber calibrated for {sup 192}Ir HDR sources. Methods: The calibration coefficients of 35 well-type ionization chambers of two different chamber types for radiation fields of {sup 60}Co and {sup 192}Ir HDR brachytherapy sources were determined experimentally. A radiation quality correction factor k{sub Q} was determined as the ratio of the calibration coefficients for {sup 60}Co and {sup 192}Ir. The dependence on chamber-to-chamber variations, source-to-source variations, and source strength was investigated. Results: For the PTW Tx33004 (Nucletron source dosimetry system (SDS)) well-type chamber, the type-specific radiation quality correction factor k{sub Q} is 1.19. Note that this value is valid for chambers with the serial number, SN ≥ 315 (Nucletron SDS SN ≥ 548) onward only. For the Standard Imaging HDR 1000 Plus well-type chambers, the type-specific correction factor k{sub Q} is 1.05. Both k{sub Q} values are independent of the source strengths in the complete clinically relevant range. The relative expanded uncertainty (k = 2) of k{sub Q} is U{sub k{sub Q}} = 2.1% for both chamber types. Conclusions: The calibration coefficient of a well-type chamber for radiation fields of {sup 60}Co HDR brachytherapy sources can be calculated from a given calibration coefficient for {sup 192}Ir radiation by using a chamber-type-specific radiation quality correction factor k{sub Q}. However, the uncertainty of a {sup 60}Co calibration coefficient calculated via k{sub Q} is at least twice as large as that for a direct calibration with a {sup 60}Co source.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Sci—Fri AM: Mountain — 03: Current status of the NRC primary standard for {sup 192}Ir HDR brachytherapy sources

The Canadian primary standard for {sup 192}Ir HDR brachytherapy sources has been recently revised in a more accurate manner allowing for more realistic uncertainty estimation. Air-kerma strength S{sub k} is derived from measurements of the source's output using a graphite-walled spherical ionization chamber (2S) at several distances. Traceability to NRC primary standards for the {sup 192}Ir calibration coefficient N{sub k} is insured by estimating it as the inverse arithmetic mean of the inverse of the calibration coefficients for a {sup 137}Cs beam and the medium energy x-ray beam quality N250, both of which are traceable to NRC primary standards. The multiple-distance method is combined with a non-linear least squares fit to determine St, while at the same time removing the effects of room scatter and position offset. The previously used shadow-cone method for directly measuring the room scatter is found to be inadequate due to the increased scatter contribution from the lead cone itself, especially at short source-detector distances. Rather than including the reported 1% difference in source strength for {sup 192}Ir HDR sources of different construction into the total uncertainty, users are cautioned that the calibration coefficient provided by NRC is only valid for a microSelectron V2 model. A comprehensive uncertainty budged shows that the total one sigma uncertainty of the standard is actually 0.6% rather than the previously assumed 1.2%. NRC measured S{sub k} agrees within 0.03% of the manufacturer's value.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

IEA-R1 Nuclear Research Reactor: 58 Years of Operating Experience and Utilization for Research, Teaching and Radioisotopes Production

IEA-R1 research reactor at the Instituto de Pesquisas Energeticas e Nucleares (Nuclear and Energy Research Institute) IPEN, Sao Paulo, Brazil is the largest power research reactor in Brazil, with a maximum power rating of 5 MWth. It is being used for basic and applied research in the nuclear and neutron related sciences, for the production of radioisotopes for medical and industrial applications, and for providing services of neutron activation analysis, real time neutron radiography, and neutron transmutation doping of silicon. IEA-R1 is a swimming pool reactor, with light water as the coolant and moderator, and graphite and beryllium as reflectors. The reactor was commissioned on September 16, 1957 and achieved its first criticality. It is currently operating at 4.5 MWth with a 60-hour cycle per week. In the early sixties, IPEN produced {sup 131}I, {sup 32}P, {sup 198}Au, {sup 24}Na, {sup 35}S, {sup 51}Cr and labeled compounds for medical use. During the past several years, a concerted effort has been made in order to upgrade the reactor power to 5 MWth through refurbishment and modernization programs. One of the reasons for this decision was to produce {sup 99}Mo at IPEN. The reactor cycle will be gradually increased to 120 hours per week continuous operation. It is anticipated that these programs will assure the safe and sustainable operation of the IEA-R1 reactor for several more years, to produce important primary radioisotopes {sup 99}Mo, {sup 125}I, {sup 131}I, {sup 153}Sm and {sup 192}Ir. Currently, all aspects of dealing with fuel element fabrication, fuel transportation, isotope processing, and spent fuel storage are handled by IPEN at the site. The reactor modernization program is slated for completion by 2015. This paper describes 58 years of operating experience and utilization of the IEA-R1 research reactor for research, teaching and radioisotopes production. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

SU-G-201-16: Thermal Imaging in Source Visualization and Radioactivity Measurement for High Dose Rate Brachytherapy

Purpose: High Dose Rate (HDR) brachytherapy poses a special challenge to radiation safety and quality assurance (QA) due to its high radioactivity, and it is thus critical to verify the HDR source location and its radioactive strength. This study demonstrates a new method for measuring HDR source location and radioactivity utilizing thermal imaging. A potential application would relate to HDR QA and safety improvement. Methods: Heating effects by an HDR source were studied using Finite Element Analysis (FEA). Thermal cameras were used to visualize an HDR source inside a plastic applicator made of polyvinylidene difluoride (PVDF). Using different source dwell times, correlations between the HDR source strength and heating effects were studied, thus establishing potential daily QA criteria using thermal imaging Results: For an Ir1?2 source with a radioactivity of 10 Ci, the decay-induced heating power inside the source is ∼13.3 mW. After the HDR source was extended into the PVDF applicator and reached thermal equilibrium, thermal imaging visualized the temperature gradient of 10 K/cm along the PVDF applicator surface, which agreed with FEA modeling. For Ir{sup 192} source activities ranging from 4.20–10.20 Ci, thermal imaging could verify source activity with an accuracy of 6.3% with a dwell time of 10 sec, and an accuracy of 2.5 % with 100 sec. Conclusion: Thermal imaging is a feasible tool to visualize HDR source dwell positions and verify source integrity. Patient safety and treatment quality will be improved by integrating thermal measurements into HDR QA procedures.

60 APPLIED LIFE SCIENCES↗