90Y Source Research Articles

Age dating of liquid 90Sr–90Y sources

In the context of age dating of 90Sr, the selective adsorption of zirconium ions from the mixture with strontium and yttrium by adsorbents based on TiO2 with a chemically modified surface was investigated. The general features of the separation process of strontium, yttrium, and zirconium in batch conditions were determined. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to analyze the initial and residual concentrations of the studied cations. Separation of 90Zr and 90Sr from a liquid source containing 90Sr–90Y using adsorbents based on TiO2 was performed for the first time. The ratio of 90Zr/90Sr was measured, and the age of liquid 90Sr–90Y sources was determined. In addition, we studied the age dating of 90Sr–90Y sources using a combination of liquid-scintillation counting of 90Sr and ICP-MS measurement. The results of both methods – the method of age-dating with the chemical separation of isotopes and the combination of LSC and ICP-MS analysis – agree very well and thus serve for cross-validation. Moreover, the combination of the two methods increases the confidence in the age-dating results of 90Sr–90Y sources.

A Facile Strategy for Preparation of Yttrium-90 Therapeutic Sources for Radionuclide Therapy.

Background: Mold brachytherapy using high-energy β--emitting radioisotopes is a promising treatment modality for skin cancers and keloids. Simple methodologies for consistent and stable incorporation of radionuclides into the matrix are desired for preparation of therapeutic sources. Methods: The authors report a facile strategy for the stable incorporation of Yttrium-90 (90Y) into amidoxime-functionalized polyacrylonitrile-polyvinylidene fluoride (PAN-PVDF) membranes. The strategy consisted of surface modification of PAN-PVDF membranes by reaction with hydroxylamine, characterization of the functionalized membranes, and optimization of experimental variables for maximum loading of 90Y onto the membranes. Quality control tests essential for confirming the suitability of the 90Y therapeutic sources for human application, such as uniformity of activity distribution, absence of leaching of activity, and estimation of surface contamination, were performed. Theoretical calculations to estimate the dose imparted by the 90Y therapeutic sources at varying depths of tissue were also carried out to predict the possible therapeutic outcome of treatment. Results: A facile method for large-scale preparation of 90Y-based mold brachytherapy sources could be established. Conclusions: The source fabrication methodology standardized in this work could be tailored for fabrication of custom-made 90Y sources for individualized treatment of superficial tumors, Bowen's disease, and keloids.

SPECT performance evaluation on image of Yttrium 90 - Bremsstrahlung using Monte Carlo simulation

Yttrium-90 (90Y) is one of the most widely used radionuclides in Nuclear Medicine practice. However, characteristic energy of this beta emitter constitutes a difficulty for dose planning using SPECT imaging. This work aimed to study bremsstrahlung X-rays effects produced by 90Y beta particles during SPECT image acquisition using Monte Carlo code MCNPX. Several simulations were carried out to evaluate different aspects that could affect SPECT image quality, such as: collimator type, source-collimator distance and composition of each interacting material. Two configurations of 90Y sources were simulated: a point source in several spheres of different materials (soft tissue, water, articular cartilage, and bone) and dimensions with radius ranging from 1 to 20 mm; and a uniformly distributed source in a Lucite cylindrical phantom filled with water. It was evaluated the bremsstrahlung photon emission generated inside different materials; for this was considered the number photons that passing through every different sphere's surface for each radii and material. In case of cylindrical phantom filled with water, in order to obtain the energy deposited over NaI (Tl) crystal detector; there was considered Median Energy General Purpose (MEGP) and Low Energy High Resolution (LEHR) collimators. Moreover, using TMESH routine available in the MCNPX Monte Carlo code, energy distribution images according to the collimator type and the source-collimator distance were obtained. The simulation was validated by comparing with the spectral distribution of the 90Y bremsstrahlung X-rays obtained experimentally from an acrylic cylindrical phantom. Results corroborated the importance of Monte Carlo simulation method to evaluate a performance of SPECT image acquisition with 90Y. The best resolution was obtained with MEGP collimator independent of source-collimator distance.

Feasibility study on the use of CMOS sensors as detectors in radioguided surgery with [formula omitted]- emitters

Radioguided surgery (RGS) is a medical practice which thanks to a radiopharmaceutical tracer and a probe allows the surgeon to identify tumor residuals up to a millimetric resolution in real-time. The employment of β− emitters, instead of γ or β+, reduces background from healthy tissues, administered activity to the patient, and medical exposure. In a previous work the possibility of using a CMOS Imager (Aptina MT9V011), initially designed for visible light imaging, to detect β− from 90Y or 90Sr sources has been established. Because of its possible application as counting probe in RGS, the performances of MT9V011 in clinical-like conditions were studied.11This work financed by Istituto Nazionale Fisica Nucleare, Italy, project CHIR2, and partially supported by Universitá degli Studi di Perugia, Italy , Fondo Ricerca di Base 2017, project SEISIPO.Through horizontal scans on a collimated 90Sr source of different sizes (1, 3, 5, 7 mm), we have determined relationships between scan fit parameters and the source dimension, namely A quadratic correlation and a linear dependency of, respectively, signal integrated over scan interval, and maximum signal against source diameter, are determined. Horizontal scan measurements on a source, interposing collimators of different size, aim to determine relationships or correlations between scan fit parameters and source dimension. A quadratic correlation and a linear dependency of, respectively, signal integrated over scan interval, and maximum signal against source diameter are determined.In order to get closer to clinical conditions, agar–agar phantoms containing 90Y with different dimensions and activities were prepared. A 90Y phantom is characterized by a central spot and a ring all around, for simulating both signal (tumor) and background (surrounding healthy tissue). The relationship found between scan maximum and 90Sr source diameter is then exploited to extract the concentration ratio between spot and external ring of the 90Y phantom. This observable, defined as the ratio between the tumor and the nearby healthy tissues uptake simulates the Tumor-to-Non-tumor Ratio (TNR). With the aim of evaluating the sensor’s ability to discriminate signal from background relying on the significance parameter, a further 90Y phantom, featuring a well-known and clinical-like activity will mimic the signal only condition. This result is used to extrapolate to different source sizes, after having estimated the background for various TNR. The obtained significance values suggest that the MT9V011 sensor is capable of distinguishing a signal from an estimated background, depending on the interplay among TNR, acquisition time and tumor diameter.

Enhancement of radiation exposure risk from β-emitter radionuclides due to Internal Bremsstrahlung effect: A Monte Carlo study of 90Y case

Employment of β-decaying radionuclides, used in many fields (industrial, clinical, research) requires a correct assessment of the operators’ radiological exposure. Usually, in the dosimetric evaluation, the contribution coming from Internal Bremsstrahlung (IB) accompanying the β-decay is not kept into account; nevertheless, this negligibility does not always appear justified, at least for high-energy β-emitters. By means of Monte Carlo (MC) simulations, we showed how the contribution from IB photons is noteworthy for the evaluation of the overall radiation absorbed dose in the case of 90Y source. We evaluated an increase of the absorbed doses, respectively for a point source and the considered receptacles, up to + 34% and + 60% or + 15% and + 28%, depending on the adopted model of IB spectrum. These results demonstrate the relevance of IB phenomenon in radiation protection estimations and suggest extending future theoretical and experimental studies to other β-decaying radionuclides.

Dosimetric characterization of a novel 90Y source for use in the conformal superficial brachytherapy device

PurposeTo characterize the dose distribution in water of a novel beta-emitting brachytherapy source for use in a Conformal Superficial Brachytherapy (CSBT) device. Methods and materialsYttrium-90 (90Y) sources were designed for use with a uniquely designed CSBT device. Depth dose and planar dose measurements were performed for bare sources and sources housed within a 3D printed source holder. Monte Carlo simulated dose rate distributions were compared to film-based measurements. Gamma analysis was performed to compare simulated and measured dose rates from seven 90Y sources placed simultaneously using the CSBT device. ResultsThe film-based maximum measured surface dose rate for a bare source in contact with the surface was 3.35 × 10–7 cGy s−1 Bq−1. When placed in the source holder, the maximum measured dose rate was 1.41 × 10–7 cGy s−1 Bq−1. The Monte Carlo simulated depth dose rates were within 10% or 0.02 cm of the measured dose rates for each depth of measurement. The maximum film surface dose rate measured using a seven-source configuration within the CSBT device was 1.78 × 10−7 cGy s−1 Bq−1. Measured and simulated dose rate distribution of the seven-source configuration were compared by gamma analysis and yielded a passing rate of 94.08%. The gamma criteria were 3% for dose-difference and 0.07056 cm for distance-to-agreement. The estimated measured dose rate uncertainty was 5.34%. Conclusions90Y is a unique source that can be optimally designed for a customized CSBT device. The rapid dose falloff provided a high dose gradient, ideal for treatment of superficial lesions. The dose rate uncertainty of the 90Y-based CSBT device was within acceptable brachytherapy standards and warrants further investigation.

Characterization of an extrapolation chamber in beta radiation beams and Monte Carlo modelling

At the Calibration Laboratory (LCI) of the IPEN/CNEN, studies are in development on the establishment of a standard composed by the beta radiation sources for the dosimetry and calibration for personal monitoring in Brazil. For this purpose is used the Böhm extrapolation chamber (PTW model 23392). This chamber was already characterized at LCI in 90Sr/90Y beams using two different entrance windows: one of aluminized Mylar and another of PET (polyethylene terephthalate) known as Hostaphan. In this work, this extrapolation chamber was characterized in 85Kr and 147Pm beams. All tests were carried out with the reference 90Sr /90Y source, for comparison purposes. The Monte Carlo code MCNP5 code was used to obtain an extrapolation chamber and the BSS2 system sources computational model, based on the determination of the absorbed dose rate. Saturation curves, ion collection efficiency, ion recombination, polarity effect, stability of response, null depth, linearity of response, variation of response as a function of source-detector distance, extrapolation curves, correction factors and absorbed dose rates were obtained. The difference between the experimental absorbed dose rates and those obtained using the Monte Carlo model, compared to those from the calibration certificates, was less than 1.9% for the 108 histories for each BSS2 system source. All results of the performed tests are within the limits of the international recommendations. The results for the 90Sr/90Y source were in good agreement with previous works performed at LCI. These results are suitable for the establishment of a standard instrument for the dosimetry and calibration of beta radiation sources and detectors in the LCI/IPEN. This standard will allow the calibration of detectors in beta radiation beams in dosimetry services in Brazil.

Monte Carlo MCNP-based simulation and radiation measurement of Yttrium-90 bremsstrahlung produced from radiation shielding apparatus

Yttrium-90 (90Y) has been widely used in therapeutic nuclear medicine including in the selective internal radiation therapy with 90Y-microsphere. In the procedure 90Y source is protected within the radiation shielding apparatus made of perspex. However, bremsstrahlung radiation may be generated when 90Y interacts with matter. The aim of this study was to evaluate bremsstrahlung radiation produced from radiation shielding apparatus using a scintillation detector and Monte Carlo simulation. The 90Y source in glass vial was placed in the radiation shielding apparatus. Bremsstrahlung measurement and spectrum were performed and recorded using thallium-doped sodium iodide (NaI(Tl)) scintillation detector. Counting time and distance between the detector and apparatus were varied to obtain the optimal condition for bremsstrahlung measurement. Monte Carlo N-Particle (MCNP) 5 was used to simulate bremsstrahlung radiation with the same geometry used in the measurement. For experimental measurement results, the optimal distance and counting time were 10 cm and 120 s, respectively. Although the result of bremsstrahlung spectrum from the detector and simulation exhibited similar trend, markedly greater count rate was observed in simulations than in detector measurements. In conclusion, 90Y bremsstrahlung can be produced from radiation protection apparatus and this can be evaluated by either measurement or simulation.

Composite thermoluminescent detectors based on the Ce3+ doped LuAG/YAG and YAG/LuAG epitaxial structures

This work presents the first results on creation of composite thermoluminescent (TL) detectors based on the film-crystal epitaxial structures of garnet compounds for the simultaneous registration of the mixed ionization fluxes containing α- and β-particles. Two types of TL detectors containing combinations of the single crystalline films (SCFs) and single crystal (SC) substrates of Ce3+ doped Y3Al5O12 (YAG) and Lu3Al5O12 (LuAG) garnets, were considered. The LuAG:Ce SCF/YAG:Ce SC and YAG:Ce SCF/LuAG:Ce SC epitaxial structures were grown by the liquid phase epitaxy (LPE) method from (overcooled) supercooled? melt-solution based on the PbO–B2O3 flux and their thermoluminescent properties were examined under excitation by α- and β-particles of 242Am' and 90Sr –90Y sources. The registration of α- and β-particles was performed using differences between TL glow curves of SCFs and substrates. The first results on separation of TL signals from SCF and SC components for LuAG:Ce SCF/YAG:Ce SC and YAG:Ce SCF/LuAG:Ce SC epitaxial structures under α- and β-excitation are encouraging. This enables consideration of these epitaxial structures as prototypes at the next steps of producing the composite TL detectors based on different oxide materials using the LPE growth method.

Evaluating the doismetric characteristics of some beta- emitter radionuclides for skin lesions irradiation

Introduction: The dosimetric characteristics of patch sources including 32P, 90Y, 188Re and 166Ho, which are employed for radionuclide skin therapy, have been evaluated in current study Materials and Methods: The patch sources understudy were modeled by MCNPX Monte Carlo code and corresponding depth dose distribution, transverse dose profile and isodose curves were calculated in a realistic model of skin phantom. Results Calculated depth dose distributions had a good accordance with those reported by other measurement studies. Comparison of the calculated depth dose distributions for radionuclides understudy showed that the 166Ho and 32P have steeper dose gradient within the depth which can improve the sparing effect for underlying healthy tissues. Symmetric variations of calculated transverse dose profiles respect to the source central axis give a desirable dose uniformity within the target area for all studied patch sources. Obtained isodose curves showed that a circular area with the diameter of around 8 mm can cover the 90% isodose for all studied beta sources. Conclusion: Based on the obtained results, it can be concluded that the 166Ho and 32P have more desirable dosimetric characteristics for irradiating the superficial skin lesions. On the other hand, irradiation of deep skin tumors through 90Y and 188Re sources will improve the treatment quality viewpoint to the better coverage of target area. Size of employed patch source should be should be selected in such a way that the delivered dose to the adjacent tissues would be minimized.

Identification of Particles of Ionizing Radiation by the Analysis of Fluorescence Pulse Form of the Thin Pen Film Scintillator

Polyethylene 2.6-naphthalate (PEN) is a promising plastic scintillator material. In this paper, a thin PEN film was used for detection, identification, and energy spectrum measurements of various ionizing radiation particles. A thin PEN film was used to separate $\alpha $ (5.49 MeV) and $\beta $ (up to 2.2 MeV) particles coming from 238Pu and 90Sr + 90Y sources, respectively, as well as for the neutron (up to 14 MeV) and gamma separation from the isotopic PuBe neutron source. Acquired photomultiplier pulses were analyzed by the long tail method based on the delayed fluorescence intensity dependence on the mass and charge of particles absorbed. For determination of the separation quality, the figure of merit (FOM), based on the ratio of short and long tails, was used. It was found that depending on the FOM values of neutron/gamma and $\alpha /\beta $ separation, the thin PEN film is suitable for the ionizing radiation particle separation.

Beta-induced decrease in the content of the Si-II, Si-XII, Si-III, and α-Si silicon phases formed under an indenter

Volumes of the metastable Si-II, Si-XII, Si-III, and α-Si silicon phases in a locally deformed (Berkovich pyramid) region of unirradiated and beforehand irradiated Si single crystals are quantitatively estimated. Experimental data obtained by Raman spectroscopy and in situ detection of Si-I → Si-II silicon phase transformations under an indenter are used to calculate the volumes. The preliminary irradiation of silicon by β particles from a 90Sr–90Y source (fluence F = 3.24 × 1010 cm–2, intensity I = 1.8 × 105 cm–2 s–1) reduces the volume of these phases by a factor of more than 1.5.

Experimental checking results of mathematical modeling of the radiation environment sensor based on diamond detectors

Were conducted a series of experiments, the purpose of which had to verify the mathematical model of the radiation environment sensor. Theoretical values of the beta particles count rate from 90Sr - 90Y source registered by radiation environment sensor was compared with the experimental one. Theoretical (calculated) count rate of beta particles was found with using the developed mathematical model of the radiation environment sensor. Deviation of the calculated values of the beta particle count rate does not exceed 10% from the experimental.

Characteristics of Bremsstrahlung emissions of 177Lu, 188Re, and 90Y for SPECT/CT quantification in radionuclide therapy

PurposeBeta particles emitted by radioisotopes used in targeted radionuclide therapies (TRT) create Bremsstrahlung (BRS) which may affect SPECT quantification when imaging these isotopes. The purpose of the current study was to investigate the characteristics of Bremsstrahlung produced in tissue by three β-emitting radioisotopes used in TRT. MethodsMonte Carlo simulations of 177Lu, 188Re, and 90Y sources placed in water filled cylinders were performed. BRS yields, mean energies and energy spectra for (a) all photons generated in the decays, (b) photons that were not absorbed and leave the cylinder, and (c) photons detected by the camera were analyzed. Next, the results of simulations were compared with those from experiments performed on a clinical SPECT camera using same acquisition conditions and phantom configurations as in simulations. ResultsSimulations reproduced relatively well the shapes of the measured spectra, except for 90Y which showed an overestimation in the low energy range. Detailed analysis of the results allowed us to suggest best collimators and imaging conditions for each of the investigated isotopes. Finally, our simulations confirmed that the BRS contribution to the energy spectra in quantitative imaging of 177Lu and 188Re could be ignored. ConclusionsFor 177Lu and 188Re, BRS contributes only marginally to the total spectra recorded by the camera. Our analysis shows that MELP and HE collimators are the best for imaging these two isotopes. For 90Y, HE collimator should be used.

Organ doses from hepatic radioembolization with 90Y, 153Sm, 166Ho and 177Lu: A Monte Carlo simulation study using Geant4

90Y-radioembolization is a palliative treatment for liver cancer. 90Y decays via beta emission, making imaging difficult due to absence of gamma radiation. Since post-procedure imaging is crucial, several theranostic radionuclides have been explored as alternatives. However, exposures to gamma radiation throughout the treatment caused concern for the organs near the liver. Geant4 Monte Carlo simulation using MIRD Pamphlet 5 reference phantom was carried out. A spherical tumour with 4.3cm radius was modelled within the liver. 1.82GBq of 90Y sources were isotropically distributed within the tumour, with no extrahepatic shunting. The simulation was repeated with 153Sm, 166Ho and 177Lu. The estimated tumour doses for all radionuclides were 262.9Gy. Tumour dose equivalent to 1.82GBq 90Y can be achieved with 8.32, 5.83, and 4.44GBq for 153Sm, 166Ho and 177Lu, respectively. Normal liver doses by the other radionuclides were lower than 90Y, hence beneficial for normal tissue sparing. The organ doses from 153Sm and 177Lu were relatively higher due to higher gamma energy, but were still well below 1Gy. 166Ho, 177Lu and 153Sm offer useful gamma emission for post-procedure imaging. They show potential as 90Y substitutes, delivering comparable tumour doses, lower normal liver doses and other organs doses far below the tolerance limit.

Development of nuclear microbattery prototype based on Schottky barrier diamond diodes

We designed, fabricated, and tested for the first time a prototype of nuclear micropower battery with an overall active area about 15 cm2 consisted in 130 single cells based on Schottky barrier diamond diodes. Diodes selection for the battery assembly was performed on the basis of I–V curves measurements at electron beam irradiation in SEM. A typical energy conversion efficiency of each cell was about 4–6%. To characterize a battery prototype performance, we carried out photovoltaic measurements using different radioisotopes. Under irradiation by 63Ni source with activity of 5 mCi cm−2, the output power density of 3 nW cm−2 was obtained. Due to large energy loss of the emitted β particles in source itself, the total battery efficiency was only 0.6%. However, with the long‐lived 63Ni isotope, this already gives the battery specific energy of about 120 W · hr/kg, comparable with the commercial chemical cells. During experiments with high activity 90Sr–90Y source, no degradation was observed after 1,400 h of the radiation exposure. The maximum output power density of 2.4 µW cm−2 was achieved using 238Pu α source. The results display that synthetic diamond is a highly promising material for nuclear microbattery fabrication. A strategy to further cell optimization is also discussed.

Monte Carlo dosimetry of a new (90)Y brachytherapy source.

PurposeIn this study, we attempted to obtain full dosimetric data for a new 90Y brachytherapy source developed by the College of Chemistry (Sichuan University) for use in high-dose-rate after-loading systems.Material and methodsThe dosimetric data for this new source were used as required by the dose calculation formalisms proposed by the AAPM Task Group 60 and Task Group 149. The active core length of the new 90Y source was increased to 4.7 mm compared to the value of 2.5 mm for the old 90Sr/90Y source. The Monte Carlo simulation toolkit Geant4 was used to calculate these parameters. The source was located in a 30-cm-radius theoretical sphere water phantom.ResultsThe dosimetric data included the reference absorbed dose rate, the radial dose function in the range of 1.0 to 8.0 mm in the longitudinal axis, and the anisotropy function with a θ in the range of 0° to 90° at 5° intervals and an r in the range of 1.0 to 8.0 mm in 0.2-mm intervals. The reference absorbed dose rate for the new 90Y source was determined to be equal to 1.6608 ± 0.0008 cGy s–1 mCi–1, compared to the values of 0.9063 ± 0.0005 cGy s–1 mCi–1 that were calculated for the old 90Sr/90Y source. A polynomial function was also obtained for the radial dose function by curve fitting.ConclusionsDosimetric data are provided for the new 90Y brachytherapy source. These data are meant to be used commercially in after-loading system.

Production and characterization of spodumene dosimetric pellets by prepared by pechini and proteic sol–gel route

Spodumene is an aluminosilicate that has proven suitable for high-dose TL dosimetry of beta or gamma rays. Due to the presence of lithium in its chemical composition (LiAlSi2O6 – β-LAS), it has potential as neutron dosimeter as well. This silicate may be obtained naturally or synthetically. The synthetic LAS has been produced by solid state reaction and conventional sol–gel, whose difficulty arises from the need to employ high temperatures and high cost reagents, respectively. Alternative routes like Pechini and proteic sol–gel methods are promising, because they can reduce production costs and the possibility of environmental pollution. This work aimed at producing spodumene with the proteic sol–gel method using edible unflavored gelatin as a precursor and also with the Pechini method. The products were characterized physically and morphologically, and their applicability as TL dosimeter was investigated, comparing the sensitivity of samples produced by different methods. Two sets of samples were produced using different sources of silicon, tetraethyl orthosilicate (TEOS, Si(C2H5O)4) and silica (SiO2). The materials produced were characterized by X-ray diffraction and by thermal analysis in order to evaluate their structural properties, as well as possible temperature-dependent changes in physical or chemical properties. The syntherized pellets produced with these crystals were irradiated with a 90Sr–90Y source and their TL glow curves were evaluated. The production of β-LAS was successful by both methods, either using silica or TEOS as a silicon source. The crystals were obtained using much lower temperatures than by methods described in literature. We observed that the method of powder production was critical to develop a radiation detector: the best TL material was the powder produced using silica and the Pechini Method.

New method to determine effective atomic number of samples via external bremsstrahlung

In the present investigation, the variation in the external bremsstrahlung (EB) intensity produced due to the beta particles emitted by the 90Sr–90Y source in the elements Al, Cu, Ag, Sn, and Pb as well as some lead compounds was studied as a function of their masses per unit area. By a suitable regression analysis, two new, handy, and simple expressions for the effective atomic number of the radiator were derived in terms of the measured EB intensity. The novelty of the present method is that these expressions require either two different samples of the same mass per unit area or a single sample of two different masses per unit area for determining the effective atomic number. To check the efficacy of the method, from the measured EB intensity of the group of lead compounds, their effective atomic number was determined by making use of these expressions. The results were found to be in good agreement with the modified atomic number Zmod, calculated by using the theoretical expression of Markowicz and Van Grieken. This establishes the fact that this new method employs simple and very handy expressions which will be convenient particularly in the case of samples which are not abundantly available in nature. Copyright © 2014 John Wiley & Sons, Ltd.

The use of the TL and OSL phenomena for determination of absorbed dose rates of 90Sr + 90Y sources by a postal method

International recommendations establish that 90Sr+90Y clinical applicators have to be calibrated in order to determine the absorbed dose rates in the case of the sources that do not have original calibration certificates, or to update the absorbed dose rates presented in the source certificates. Following these recommendations, a postal dosimetric system was developed to calibrate clinical applicators using two luminescent techniques: thermoluminescence (TL) and optically stimulated luminescence (OSL). In this work, Al2O3:C commercial detectors were characterized and their TL and OSL responses were analyzed. The results showed the efficiency and the optimal behavior of this material in beta radiation beams. After characterization, the system was sent to the Federal University of Sergipe (UFS), Brazil, for calibration of five 90Sr+90Y clinical applicators, where the detectors were irradiated and returned to IPEN, for their evaluation and determination of the absorbed dose rates. A comparison between these absorbed dose rates and those adopted by the UFS as original was made; the differences obtained were within those of other studies, and they demonstrated the usefulness of the system.