Types Of Dosimeters Research Articles

A comparative study of small field total scatter factors and dose profiles using plastic scintillation detectors and other stereotactic dosimeters: The case of the CyberKnife

Small-field dosimetry is challenging, and the main limitations of most dosimeters are insufficient spatial resolution, water nonequivalence, and energy dependence. The purpose of this study was to compare plastic scintillation detectors (PSDs) to several commercial stereotactic dosimeters by measuring total scatter factors and dose profiles on a CyberKnife system. Two PSDs were developed, having sensitive volumes of 0.196 and 0.785 mm(3), and compared with other detectors. The spectral discrimination method was applied to subtract Čerenkov light from the signal. Both PSDs were compared to four commercial stereotactic dosimeters by measuring total scatter factors, namely, an IBA dosimetry stereotactic field diode (SFD), a PTW 60008 silicon diode, a PTW 60012 silicon diode, and a microLion. The measured total scatter factors were further compared with those of two independent Monte Carlo studies. For the dose profiles, two commercial detectors were used for the comparison, i.e., a PTW 60012 silicon diode and Gafchromics EBT2. Total scatter factors for a CyberKnife system were measured in circular fields with diameters from 5 to 60 mm. Dose profiles were measured for the 5- and 60-mm cones. The measurements were performed in a water tank at a 1.5-cm depth and an 80-cm source-axis distance. The total scatter factors measured using all the detectors agreed within 1% with the Monte Carlo values for cones of 20 mm or greater in diameter. For cones of 10-20 mm in diameter, the PTW 60008 silicon diode was the only dosimeter whose measurements did not agree within 1% with the Monte Carlo values. For smaller fields (<10 mm), each dosimeter type showed different behaviors. The silicon diodes over-responded because of their water nonequivalence; the microLion and 1.0-mm PSD under-responded because of a volume-averaging effect; and the 0.5-mm PSD was the only detector within the uncertainties of the Monte Carlo simulations for all the cones. The PSDs, the PTW 60012 silicon diode, and the Gafchromics EBT2 agreed within 2% and 0.2 mm (gamma evaluation) for the measured dose profiles except in the tail of the 60-mm cone. Silicon diodes can be used to accurately measure small-field dose profiles but not to measure total scatter factors, whereas PSDs can be used to accurately measure both. The authors' measurements show that the use of a 1.0-mm PSD resulted in a negligible volume-averaging effect (under-response of ≈1%) down to a field size of 5 mm. Therefore, PSDs are strong candidates to become reference radiosurgery detectors for beam characterization and quality assurance measurements.

Aspects of forward scattering from the compression paddle in the dosimetry of mammography

The best compression paddle position during air kerma measurement in mammography dosimetry was studied. The amount of forward scattering as a function of the compression paddle distance was measured with different X-ray spectra and different types of paddles and dose meters. The contribution of forward scattering to the air kerma did not present significant dependency on the beam quality or of the compression paddle type. The tested dose meter types detected different amounts of forward scattering due to different internal collimation. When the paddle was adjusted to its maximum clinical distance, the proportion of the detected forward scattering was only 1 % for all dose meter types. The most consistent way of performing air kerma measurements is to position the compression paddle at the maximum distance from the dose meter and use a constant forward scattering factor for all dose meters. Thus, the dosimetric uncertainty due to the forward scatter can be minimised.

Errors introduced by dose scaling for relative dosimetry

Some dosimeters require a relationship between detector signal and delivered dose. The relationship (characteristic curve or calibration equation) usually depends on the environment under which the dosimeters are manufactured or stored. To compensate for the difference in radiation response among different batches of dosimeters, the measured dose can be scaled by normalizing the measured dose to a specific dose. Such a procedure, often called “relative dosimetry”, allows us to skip the time‐consuming production of a calibration curve for each irradiation. In this study, the magnitudes of errors due to the dose scaling procedure were evaluated by using the characteristic curves of BANG3 polymer gel dosimeter, radiographic EDR2 films, and GAFCHROMIC EBT2 films. Several sets of calibration data were obtained for each type of dosimeters, and a calibration equation of one set of data was used to estimate doses of the other dosimeters from different batches. The scaled doses were then compared with expected doses, which were obtained by using the true calibration equation specific to each batch. In general, the magnitude of errors increased with increasing deviation of the dose scaling factor from unity. Also, the errors strongly depended on the difference in the shape of the true and reference calibration curves. For example, for the BANG3 polymer gel, of which the characteristic curve can be approximated with a linear equation, the error for a batch requiring a dose scaling factor of 0.87 was larger than the errors for other batches requiring smaller magnitudes of dose scaling, or scaling factors of 0.93 or 1.02. The characteristic curves of EDR2 and EBT2 films required nonlinear equations. With those dosimeters, errors larger than 5% were commonly observed in the dose ranges of below 50% and above 150% of the normalization dose. In conclusion, the dose scaling for relative dosimetry introduces large errors in the measured doses when a large dose scaling is applied, and this procedure should be applied with special care.PACS numbers: 87.56.Da, 06.20.Dk, 06.20.fb

High resolution 2D dose measurement device based on a few long scintillating fibers and tomographic reconstructiona)

Patient-specific QA of highly conformal radiotherapy treatments are usually conducted using 2D or 3D dosimetry of the incident dose distribution in a water-equivalent phantom. However, dosimeters typically used for this task usually lack in either spatial resolution or dose accuracy. The purpose of this work is to develop and validate a novel type of high resolution 2D dosimeter based on the tomographic reconstruction of the dose projections obtained using long scintillating fibers for the quality assurance of modern radiotherapy techniques such as IMRT. Fifty parallel scintillating fibers were aligned in a 30 cm diameter cylindrical masonite phantom with a 95 cm source-to-surface distance and a 100 cm source-to-fibers distance. The fibers were disposed so that the effective detection area of the scintillating fibers was a 20 cm diameter disk. Both ends of each scintillating fiber were coupled to clear optical fibers to enable light collection by a single CCD camera. Seven IMRT segments and two square fields were acquired using 18 projections over a 170° rotation of the device. Computation of the dose integrals was made for each scintillating fiber using the irradiation of known rectangular reference fields. Dose reconstructions were conducted using a total-variation minimization iterative reconstruction algorithm. Eight monitor units were programmed for each projection and the reconstructed dose grid pixel resolution was set to 1 × 1 mm(2). 3%∕3 mm gamma tests conducted between the reconstructed IMRT dose distributions and the dose calculated with the treatment planning system Pinnacle(3) were on average successful for 99.6% of the dose pixels with a predicted dose of at least 10% of the maximum dose. The dose profiles for both square fields and IMRT segments agreed within 2% to the dose calculated with Pinnacle(3) except in high dose gradient regions, and were comparable to the dose measured using an ionization chamber array (IBA MatriXX) and radiographic films (Kodak XV2). Using tomographic reconstruction on the projections acquired with rotating scintillating fibers, we were able to perform water-equivalent 2D dosimetry of square fields and IMRT segments with acceptable accuracy and high spatial resolution. The underlying concept of tomographic dosimetry and the small number of fibers needed to reconstruct a given 2D dose distribution offer new dosimetric possibilities, both applicable to 2D and 3D dosimetry.

Estudo da resposta de um dosímetro eletrónico individual

Introduction – The measurement of occupational exposure to radiation doses can be completed with an electronic personal dosemeter that allows a direct reading and alarm function of the received radiation dose. Due to the energy and dose rate dependence already reported for this type of dosemeter, it is intended, with this work, to determine the response linearity of an Electronic Personal Dosemeter and to study its response behavior to the dose rate and radiation energy. Methodology – The electronic personal dosemeter Vertec Bleeper Sv energy dependency was evaluated by its irradiation with 500 μSv from the radionuclides Cobalt – 60 (60C) and Cesium – 137 (137Cs) as well as by the radiation qualities of the Narrow (N) series: N‑30, N‑40, N‑60, N‑80, N‑100 e N‑120. To investigate the dose rate dependency, the intensities of electric current of 1 mA, 5 mA, 10 mA, 15 mA and 20 mA were applied to the X‑ray tube. Results – There is no relationship between the response of the detector and the radiation energy. For energies below 33 keV there is an underestimation over 50% of the radiation dose measured but the detector presents a linear response for energies under 100 μSv. A dependency on the dose rate is perceived since as the dose rate increases, the response of the individual monitor decreases. There is a smaller decrease for the radiation qualities of N‑30 (1.1%), N‑40 (4.1%) and N‑120 (20.0%). Conclusion – It is concluded that there is a strong dependence of radiation energy and dose rate on the response of an electronic personal dosemeter.

Electrospun copper oxide nanofibers for H2S dosimetry

AbstractWe present the preparation and characterization of a novel copper(II)oxide (CuO) nanofiber based sensor with very high sensitivity and selectivity to hydrogen sulfide (H2S). The working principle is based on the phase transition of semiconducting p‐type CuO to strongly degenerated p‐type copper sulfide (CuS) with metallic conductivity. Electrospun polymer fiber networks of polyvinyl butyrate (PVB) and Cu(NO3)2 were attached on standard gas sensing substrates and calcined to CuO at 600 °C in ambient air for 24 h. Continuous exposure to H2S (0.1–5 ppm) as well as a sequence of 1 ppm H2S pulses result in a dosimeter type behavior of the nanofiber sensors. Triggered by a certain dose (gas concentration multiplied by time) a steep conductance increase of the sensitive layer over several orders of magnitude is observed. After reaching this percolation threshold only small conductance changes were observed. These fiber based sensors show a remarkably high specificity, there is no response to carbon monoxide, hydrogen, and methane at 160 °C. The fiber network can be regenerated by raising the operating temperature to 350 °C for 30 min in absence of H2S. magnified image Conductance change under exposure to various gases. Continuous recording with one measurement per second.

Application of element correction and personal dose equivalent response to extremity dosimeters used at Korean nuclear power plants

Radiation workers who inspect and repair steam generators during maintenance periods in nuclear power plants (NPPs) have a likelihood of high radiation exposure to their extremities, especially the hands, because of contact with radioactive materials. To estimate the personal dose equivalent, Hp(0.07) to an extremity, it is necessary for workers to wear extremity dosimeters, thermoluminescent dosimeters (TLD), on their fingers. In this article, the element correction and the personal dose equivalent response for two types of extremity dosimeters, Harshaw EXTRAD dosimeters and Panasonic UD‐807 dosimeters, which are currently available at Korean NPPs, were calculated by calibration and irradiation tests. To provide the characteristics of the incident radiation field for contact tasks, the results of a radiation field test for inhomogeneous radiation fields in Korean NPPs were also introduced. Finally, on the basis of the results of calibration, irradiation, and radiation field tests, the application of element correction and personal dose equivalent response to extremity dosimeters for radiation workers at Korean NPPs was evaluated in terms of practical use.

An investigation into the sensitivity of various albedo neutron dosimeters aimed at correcting the readings

The results of an experimental determination of the sensitivity of three types of individual neutron albedo dosimeters in neutron reference fields on the basis of radionuclide sources and at the top concrete shielding of the U-70 accelerator are presented. The results show that the ratios between the responses of the albedo dosimeters designed earlier at the Joint Institute for Nuclear Research (the albedo dosimeter (AD) and the multicomponent dosimeter (MD)) and the currently used DVGN-01 dosimeter are constant within 25% in a wide range of neutron energy. This fact makes it possible to use the results of measuring the AD and MD responses obtained earlier in neutron fields of nuclear-physical installations at the Joint Institute for Nuclear Research (JINR) for the correction of DVGN-01 dosimeter measurement results to apply it to personal radiation monitoring (PRM) at these installations. The correction factors for DVGN-01 measurement results are found and recommended to be used in PRM for most JINR installations.

A Critical Assessment of Two Types of Personal UV Dosimeters

Doses of erythemally weighted irradiances derived from polysulphone (PS) and electronic ultraviolet (EUV) dosimeters have been compared with measurements obtained using a reference spectroradiometer. PS dosimeters showed mean absolute deviations of 26% with a maximum deviation of 44%, the calibrated EUV dosimeters showed mean absolute deviations of 15% (maximum 33%) around noon during several test days in the northern hemisphere autumn. In the case of EUV dosimeters, measurements with various cut-off filters showed that part of the deviation from the CIE erythema action spectrum was due to a small, but significant sensitivity to visible radiation that varies between devices and which may be avoided by careful preselection. Usually the method of calibrating UV sensors by direct comparison to a reference instrument leads to reliable results. However, in some circumstances the quality of measurements made with simple sensors may be over-estimated. In the extreme case, a simple pyranometer can be used as a UV instrument, providing acceptable results for cloudless skies, but very poor results under cloudy conditions. It is concluded that while UV dosimeters are useful for their design purpose, namely to estimate personal UV exposures, they should not be regarded as an inexpensive replacement for meteorological grade instruments.

In vivodosimetry with optically stimulated luminescent dosimeters, OSLDs, compared to diodes; the effects of buildup cap thickness and fabrication material

For external beam in vivo measurements, the dosimeter is normally placed on the patient's skin, and the dose to a point of interest inside the patient is derived from surface measurements. In order to obtain accurate and reliable measurements, which correlate with the dose values predicted by a treatment planning system, a dosimeter needs to be at a point of electronic equilibrium. This equilibrium is accomplished by adding material (buildup) above the detector. This paper examines the use of buildup caps in a clinical setting for two common detector types: OSLDs and diodes. Clinically built buildup-caps and commercially available hemispherical caps are investigated. The effects of buildup cap thickness and fabrication material on field-size correction factors, C(FS), are reported, and differences between the effects of thickness and fabrication material are explained based on physical parameters. Measurements are made on solid water phantoms for 6 and 15 MV x-ray beams. Two types of dosimeters are used: OSLDs, InLight∕OSL Nanodot dosimeters (Landauer, Inc., Glenwood, IL) and a P-type surface diode (Standard Imaging, Madison, WI). Buildup caps for these detectors were fabricated out of M3, a water-equivalent material, and sheet-metal stock of Al, Cu, and Pb. Also, commercially available hemispherical buildup caps made of plastic water and brass (Landauer, Inc., Glenwood, IL) were used with Nanodots. OSLDs were read with an InLight microStar reader (Landauer, Inc., Glenwood, IL). Dose calculations were carried out with the XiO treatment planning system (CMS∕Elekta, Stockholm) with tissue heterogeneity corrections. For OSLDs and diodes, when measurements are made with no buildup cap a change in C(FS) of 200% occurs for a field-size change from 3 cm × 3 cm to 30 cm × 30 cm. The change in C(FS) is reduced to about 4% when a buildup cap with wall thickness equal to the depth of maximum dose is used. Buildup caps with larger wall thickness do not cause further reduction in C(FS). The buildup cap fabrication material has little or no effect on C(FS). The perturbation to the delivered dose caused by placing a detector with a buildup cap on the surface of a patient is measured to be 4%-7%. A comparison between calculated dose and dose measured with a Nanodot and a diode for 6 and 15 MV x-rays is made. When C(FS) factors are carefully determined and applied to measurements made on a phantom, the differences between measured and calculated doses were found to be between ±1.3%. OSLDs and diodes with appropriate buildup caps can be used to measure dose on the surface of a patient and predict the delivered dose to depth dmax in a range of ±1.3% for 100 cGy. The buildup cap: can be fabricated from any material examined in this work, is best with wall thickness dmax, and causes a perturbation to the delivered dose of 4%-7% when the wall thickness is dmax. OSLDs and diodes with buildup caps can both give accurate measurements of delivered dose.

DEVELOPMENT AND EVALUATION OF A PHANTOM FOR MULTI-PURPOSE DOSIMETRY IN INTENSITY-MODULATED RADIATION THERAPY

A LEGO-type multi-purpose dosimetry phantom was developed for intensity-modulated radiation therapy (IMRT), which requires various types of challenging dosimetry. Polystyrene, polyethylene, polytetrafluoroethylene (PTFE), and polyurethane foam (PU-F) were selected to represent muscle, fat, bone, and lung tissue, respectively, after considering the relevant mass densities, elemental compositions, effective atomic numbers, and photon interaction coefficients. The phantom, which is composed of numerous small pieces that are similar to LEGO blocks, provides dose and dose distribution measurements in homogeneous and heterogeneous media. The phantom includes dosimeter holders for several types of dosimeters that are frequently used in IMRT dosimetry. An ion chamber and a diode detector were used to test dosimetry in heterogeneous media under radiation fields of various sizes. The data that were measured using these dosimeters were in disagreement when the field sizes were smaller than 1.5 x 1.5 ㎠ for polystyrene and PTFE, or smaller than 3 x 3 ㎠ for an air cavity. The discrepancy was as large as 41% for the air cavity when the field size was 0.7 x 0.7 ㎠, highlighting one of the challenges of IMRT small field dosimetry. The LEGO-type phantom is also very useful for two-dimensional dosimetry analysis, which elucidates the electronic dis-equilibrium phenomena on or near the heterogeneity boundaries.

Measuring pacemaker dose: A clinical perspective

Recently in our clinic, we have seen an increased number of patients presenting with pacemakers and defibrillators. Precautions are taken to develop a treatment plan that minimizes the dose to the pacemaker because of the adverse effects of radiation on the electronics. Here we analyze different dosimeters to determine which is the most accurate in measuring pacemaker or defibrillator dose while at the same time not requiring a significant investment in time to maintain an efficient workflow in the clinic. The dosimeters analyzed here were ion chambers, diodes, metal-oxide-semiconductor field effect transistor (MOSFETs), and optically stimulated luminescence (OSL) dosimeters. A simple phantom was used to quantify the angular and energy dependence of each dosimeter. Next, 8 patients plans were delivered to a Rando phantom with all the dosimeters located where the pacemaker would be, and the measurements were compared with the predicted dose. A cone beam computed tomography (CBCT) image was obtained to determine the dosimeter response in the kilovoltage energy range. In terms of the angular and energy dependence of the dosimeters, the ion chamber and diode were the most stable. For the clinical cases, all the dosimeters match relatively well with the predicted dose, although the ideal dosimeter to use is case dependent. The dosimeters, especially the MOSFETS, tend to be less accurate for the plans, with many lateral beams. Because of their efficiency, we recommend using a MOSFET or a diode to measure the dose. If a discrepancy is observed between the measured and expected dose (especially when the pacemaker to field edge is <10 cm), we recommend analyzing the treatment plan to see whether there are many lateral beams. Follow-up with another dosimeter rather than repeating multiple times with the same type of dosimeter. All dosimeters should be placed after the CBCT has been acquired.

Neutron beam preparation with Am–Be source for analysis of biological samples with PGNAA method

Material analysis with prompt gamma neutron activation analysis (PGNAA) requires a proper geometrical arrangement for equipments in laboratory. Application of PGNAA in analysis of biological samples, due to small size of sample, needs attention to the dimension of neutron beam. In our work, neutron source has been made of 241Am–Be type. Activity of 241Am was 20 Ci which lead to neutron source strength of 4.4 × 107 neutrons per second. Water has been considered as the basic shielding material for the neutron source. The effect of various concentration of boric acid in the reduction of intensity of fast and thermal components of the neutron beam and gamma ray has been investigated. Gamma ray is produced by (α, n) reaction in Am–Be source (4.483 MeV), neutron capture by hydrogen (2.224 MeV), and neutron capture by boron (0.483 MeV). Various types of neutron and gamma ray dosimeters have been employed including BF3 and NE-213 detectors to detect fast and thermal neutrons. BGO scintillation detector has been used for gamma ray spectroscopy. It is shown that the gamma and neutron radiation dose due to direct beam is of the same magnitude as the dose due to radiation scattered in the laboratory ambient. It is concluded that 14 kg boric acid dissolved in 1,000 kg water is the optimum solution to surround the neutron source. The experimental results have been compared with Monte Carlo simulation.

Measurement of radon concentration for assessment of the radiological hazard in theChakwal coalmines of the Salt Range, Pakistan

Radon and its progeny are prevalent everywhere on the lithosphere especially in the miningenvironment. Coal exists in the Salt Range that passes through Pakistan. The aim of thepresent study was to measure radon concentration and assess the associated radiologicalhazard in the coalmines developed in that portion of the Salt Range which passesthrough the district of Chakwal in Pakistan. Among the various coalmines inthe coalfield, five were selected for radon survey. A passive integrated techniqueconsisting of SSNTDs (solid state nuclear track detectors) was employed for themeasurement of radon concentration in these coalmines. Box type dosimeters containingCN-85 detectors were placed for three months at six locations in every selectedcoalmine. After removing the dosimeters, the CN-85 detectors were etched inalkaline solution to enlarge the alpha tracks in the detectors and counted under anoptical microscope. The track densities were converted to radon concentration.The average concentration of radon in the coalmines varied in the range 50–114 Bq m−3. Radon exhalation rates from the samples of coal and shale collected from thecoalmines were determined to be respectively 934 (830–1010) and 1302 (1020–1580) mBq m−2 h−1. The radiation dose and corresponding health risk for the mine workers were alsoestimated.

A new personal dosimetry system for HP(10) and HP(0.07) photon dose based on OSL-dosimetry of beryllium oxide

Abstract In recent years the personal dosimetric system “iBeOx” using optically stimulated luminescence of beryllium oxide (BeO) has been developed by the TU Dresden radiation physics group in cooperation with the Helmholtz Zentrum Muenchen and IBA Dosimetry GmbH Schwarzenbruck. Continuous wave stimulation with a blue LED and measurement of the luminescence light with an enclosed photo sensor module are performed from opposite detector sides. A microcontroller controls the complete measurement cycle, processes the digitized signals, performs extensive checks of the system states and communicates via USB with the external PC software. The resulting OSL signal can be used for dose evaluation. Two types of personal dosimeters are available, both conform to the IEC 62387-1 standard. The dose response is linear from the lowest detection limit of 50 μSv–10 Sv. Long-term fading of the signal is negligible. Due to the near tissue equivalence and the resulting low photon energy dependence of BeO the personal dose can be evaluated from 12 keV up to 7 MeV by one dosimetric element without any corrections. In an automatized environment the system is able to process several hundred dosimeters per hour.

Impact of reading pre-irradiation background signal on the post-irradiation glow curves of thermoluminescence dosimeters

Due to their sensitivity, signal reproducibility and stability, lithium fluoride thermoluminescence dosimeters are widely used in many applications. It was noticed that post-irradiation glow curves of LiF dosimeters that had undergone pre-irradiation background dose measurements dramatically differed from the curves of dosimeters irradiated without such preliminary measurements. Three types of dosimeters were studied in this respect, namely, TLD-700, TLD-600, and TLD-100. Impact of pre-irradiation background measurements on the glow curve areas, peak positions, and individual peak intensities were investigated using computerized glow curve analysis. Similarities in the behavior of the dosimeters of all three types were found. Areas of the glow peaks P 2a, P 3, P 4, P 5, and P 6 increased. Peak P 3 grew most significantly, followed by P 2, and P 5. Also, one of the common features was a shift of T max of P 5 to higher temperatures. Pre-irradiation background readings increase the total area of the glow curve in general and affect relative intensities and positions of specific peaks, which changes the shape of the glow curve. It is strongly recommended to perform pre-irradiation background measurements for all LiF-based dosimeters regardless of the values of the background doses relative to the radiation doses to be given.

The use of different types of thermoluminescent dosimeters to measure extremity doses in nuclear medicine

Abstract Depth–dose curves in LiF detectors of different effective thicknesses, together with their responses, were calculated for typical nuclear medicine radiation fields with 99mTc, 18F and 90Y sources. Responses were analysed in function of the radionuclide, detector effective thickness and irradiation geometry. On the other hand the results of the nuclear medicine measurement campaign of the ORAMED project were presented focussing on the dose distribution across the hand and on the appropriate position to wear the dosimeter. According to the results, thin LiF detectors provide better responses in all cases. Its use is essential for 18F, since thick dosimeters can underestimate Hp(0.07) up to a 50% because of the very inhomogeneous dose deposition on the active layer. The preliminary results of the measurement campaign showed that the index tip of the non-dominant hand is usually the most exposed position among the 22 monitored positions. It was also found that, in average, wrist dosimeters are likely to underestimate the maximum skin dose by a factor of the order of 20. This factor is reduced to around 6 for a ring dosimeter worn on the base of the index of the non-dominant hand. Thus, for typical nuclear medicine procedures, the base of the index of the non-dominant hand is recommended as the best monitoring option.

TL measurement of ambient dose at a Nuclear Medicine Department

Abstract An investigation of ambient dose at the Nuclear Medicine Department, Instituto Nacional de Cancerologia, Mexico, was performed using two types of thermoluminescent dosemeters: TLD-100 and TLD-900. In addition, ambient dose was measured at the outside corridor of the hospitalization room for 137 Cs brachytherapy patients. Radionuclides used at the Nuclear Medicine Department are 131 I, 18 F, 67 Ga, 99m Tc, 111 In, 201 Tl. Main gamma emission energies from these elements are in the range from 93 to 511 keV. High dose values were obtained at the waste storage room, the outside corridor of 131 I patients, the PET/CT room and the outside corridor of 137 Cs brachytherapy patients. The maximum ambient dose equivalent rate equal to about 19 μSv/h was obtained for the 137 Cs brachytherapy corridor. Sites with minimum doses are the gamma camera rooms, having ambient dose equivalent rates equal to about 0.05 μSv/h. At most sites where both types of dosemeters were placed ambient dose equivalent values obtained with TLD-900 were 25–45% higher than TLD-100 values. This result was attributed to scattered radiation producing low energy photons which results in over response of TLD-900 and thus, TLD-100 values are considered to be more reliable. Knowledge of ambient dose values is relevant to the occupational exposure personnel who may limit the time spent at high dose areas. Recommendations were given to the Department authorities to implement actions in order to reduce doses at high dose sites in order to comply with the ALARA principle.

EURADOS intercomparisons on whole body and extremity dosemeters (2008–2009) – Results and comparison of different dosemeter designs

Abstract The EURADOS (European Radiation Dosimetry Group) working group (WG2) on Harmonisation of Individual Monitoring in Europe has shown that intercomparisons are fundamental for harmonisation of individual monitoring. As a result of these considerations, EURADOS started to prepare a series of continuous intercomparisons for individual monitoring services (IMS) in Europe. EURADOS has now successfully executed two intercomparison exercises, one for whole body dosemeters (2008) and one for extremity dosemeters (2009). Both exercises were performed without external funding, all costs being covered by the participants’ fees. More than 120 (!) different – mainly passive – dosimetry systems were tested from all over Europe until now and the results were analysed and compared. Although scientific studies were not the primary objective of these exercises specific additional information about the tested systems supplied by the participants for statistical analysis allows a detailed analysis of these results with respect to different parameters like dosemeter type, detector material, filter thickness or others design parameters. The influence of such parameters on the response values of the dosemeters is analysed and discussed in this paper. Both energy response as well as directional response for beta and photon radiation are considered. The influence of different design parameters e.g. detector material, is analysed by comparing the frequency distribution of the response values for different dosemeter groups. Pronounced differences for different detector materials (LiF:Mg,Ti, LiF:Mg,Cu,P and Li2B4O7/CaSO4) were found. The paper gives a comprehensive overview on the performance of various European dosimetry services and the influence of the dosemeter design on the resulting response values.

SU-E-T-222: Performance Comparison of In-Vivo Dosimeters, including TLDs, MOSFETs, and OSLDs for Patients Receiving Total Body Irradiation

Purpose: To compare accuracy of in vivo dosimeters such as TLDs,MOSFETs & OSLDs for patients receiving Total Body Irradiation. Methods: Three types of dosimeters were considered for this study, LiF Thermoluminescent Dosimeters, Modified Field Effect Transistors(MOSFET ‐Thomson&Nielsen TN‐502RD) and Optically Stimulated Luminescence Dosimeters(OSLD ‐ Landuer's 2% screened nanoDOTs). All three dosimeters were calibrated under full bulildup conditions at 100cm SSD, dmax = 3.4cm for 18MV photon energy and appropriate correction factors were applied for TBI treatment condition. This study is performed on a 30×30×22cm solid water phantom and a rando phantom at the TBI treatment distance. The separations at different locations for phantom were measured and MUs were calculated to deliver 100cGy at the midplane . Dosimeters were placed on the entrance side of the phantoms to measure dmax dose. Each type of dosimeters were irradiated at five locations in the rando phantom under the same treatment setup. The reproducibility of the dosimeters was verified by solidwater phantom measurements. Ten TBI cases, which were monitored using each dosimeter type were selected and tabulated the percentage difference of measured to expected dose for 5 different patient locations. Results: The reproducibility for TLDs,MOSFETs and OSLDs were 118.3cGy +/− 2.7%(1SD), 118.3cGy +/−2.1%(1SD) and 118.3cGy +/− 1.8%(1SD) resp after 10 consecutive measurements in solidwater phantom (Table 1). From rando phantom measurements, maximum percentage variation of the measured to expected dose with 1SD values are TLDs (1.4 +/− 1.4), MOSFETs (3.9+/− 2.2) and OSLDs (1.6 +/− 1.8) (Table 2). Percentage difference of the measured dose to expected dose for 10 clinical cases were TLDs (2.3+/− 2.9), MOSFETs (3.7+/− 4.9) and OSLDs (1.8+/− 2.9%) (Table 3). Conclusions: Measured values were within +/−5% tolerance level for all dosimeters. OSLDs can give more accurate and reproducible results with an added advantage of ease of use and shorter readout period.