Lead Collimator Research Articles

Investigation of Main Radiation Source above Shield Plug of Unit 3 at Fukushima Daiichi Nuclear Power Station

Pulse height distributions were measured using a CdZnTe detector inside a lead collimator to investigate main source producing high dose rates above the shield plugs of Unit 3 at Fukushima Daiichi Nuclear Power Station. It was confirmed that low energy photons are dominant. Concentrations of Cs-137 under 60 cm concrete of the shield plug were estimated to be between 8.1E+9 and 5.7E+10 Bq/cm2 from the measured peak count rate of 0.662 MeV photons. If Cs-137 was distributed on the surfaces of the gaps with radius 6m and with the averaged concentration of 5 points, 2.6E+10 Bq/cm2, total amount of Cs-137 is estimated to be 30 PBq.

The experimental determination of the 238U(n,γ) and total fission reaction rates along the pellet radius of the IPEN/MB-01 reactor

This work presents a new experimental approach to determine experimentally the reaction rate along the pellet radius of a research reactor facility. The methodology employs concentric hollow cylindrical lead collimators together with gamma-ray spectrometry in a special kind of HPGe detector for the discrimination of very low gamma energy emitted by 239Np and 99Mo. The 238U neutron capture and total fission rates were inferred, respectively, from the 106.2keV gamma emitted by 239Np and from the 140.51keV gamma-ray emitted by 99Mo. These lower gamma-ray energies allow the thickness of the lead collimator to be small enough so that the correction factors applied to the procedure were minimized. This kind somewhat challenging experiment was successfully performed at the IPEN/MB-01 research reactor facility. The experiments are claimed to be well-defined, and they are suitable for a benchmark. The measured values of the total fission rates are mainly due to the thermal fissions in 235U since in the IPEN/MB-01 reactor nearly 85% of the total fissions occur in the thermal neutron energy region. The theoretical analyses were performed using MCNP-5 together with the ENDF/B-VII.0 library. The analyses reveal a very good agreement between the calculated and experimental results for the 238U epithermal neutron capture reaction rates. However, the same can not be said for the thermal reaction rates which show discrepancies both in magnitude as well as in the shape of the attenuation of the reaction rates inside of the fuel pellet. The suspected reason for these discrepancies is the shape of the 235U cross sections below 0.3eV which might be different from that adopted in the ENDF/B-VII.0 library.

Characterization of "γ-Eye": a Low-Cost Benchtop Mouse-Sized Gamma Camera for Dynamic and Static Imaging Studies.

Several preclinical imaging systems are commercially available, but their purchase and maintenance costs make them unaffordable for the majority of small- and medium-sized groups. Taking into account the needs of average users, we developed "γ-eye", a mouse-sized, benchtop γ-camera suitable for in vivo scintigraphic imaging. The γ-eye is based on two position-sensitive photomultiplier tubes, coupled to a CsI(Na) pixelated scintillator and a low-energy lead collimator with parallel hexagonal holes. The spatial resolution of the system is 2mm at 0mm. The energy resolution is 26% at 140keV and the maximum recorded sensitivity 210 cps/MBq. The system was evaluated in a proof-of-concept animal study, using three different clinical Tc-99m-labeled radiopharmaceuticals. Phantom and animal studies demonstrate its ability to provide semiquantitative results even for short scans. Systems' performance, dimensions, and cost make γ-eye a unique solution for efficient whole-body mouse nuclear imaging.

Sci‐Thur PM – Brachytherapy 05: Surface Collimation Applied to Superficial Flap High Dose‐Rate Brachytherapy

Purpose:To apply surface collimation for superficial flap HDR skin brachytherapy utilizing common clinical resources and to demonstrate the potential for OAR dose reduction within a clinically relevant setting.Methods:Two phantom setups were used. 3 mm lead collimation was applied to a solid slab phantom to determine appropriate geometries relating to collimation and dwell activation. The same collimation was applied to the temple of an anthropomorphic head phantom to demonstrate lens dose reduction. Each setup was simulated and planned to deliver 400 cGy to a 3 cm circular target to 3 mm depth. The control and collimated irradiations were sequentially measured using calibrated radiochromic films.Results:Collimation for the slab phantom attenuated the dose beyond the collimator opening, decreasing the fall‐off distances by half and reducing the area of healthy skin irradiated. Target coverage can be negatively impacted by a tight collimation margin, with the required margin approximated by the primary beam geometric penumbra.Surface collimation applied to the head phantom similarly attenuated the surrounding normal tissue dose while reducing the lens dose from 84 to 68 cGy. To ensure consistent setup between simulation and treatment, additional QA was performed including collimator markup, accounting for collimator placement uncertainties, standoff distance verification, and in vivo dosimetry.Conclusions:Surface collimation was shown to reduce normal tissue dose without compromising target coverage. Lens dose reduction was demonstrated on an anthropomorphic phantom within a clinical setting. Additional QA is proposed to ensure treatment fidelity.

Pin-photodiode array for the measurement of fan-beam energy and air kerma distributions of X-ray CT scanners

PurposePatient dose estimation in X-ray computed tomography (CT) is generally performed by Monte Carlo simulation of photon interactions within anthropomorphic or cylindrical phantoms. An accurate Monte Carlo simulation requires an understanding of the effects of the bow-tie filter equipped in a CT scanner, i.e. the change of X-ray energy and air kerma along the fan-beam arc of the CT scanner. To measure the effective energy and air kerma distributions, we devised a pin-photodiode array utilizing eight channels of X-ray sensors arranged at regular intervals along the fan-beam arc of the CT scanner. MethodsEach X-ray sensor consisted of two plate type of pin silicon photodiodes in tandem – front and rear photodiodes – and of a lead collimator, which only allowed X-rays to impinge vertically to the silicon surface of the photodiodes. The effective energy of the X-rays was calculated from the ratio of the output voltages of the photodiodes and the dose was calculated from the output voltage of the front photodiode using the energy and dose calibration curves respectively. ResultsThe pin-photodiode array allowed the calculation of X-ray effective energies and relative doses, at eight points simultaneously along the fan-beam arc of a CT scanner during a single rotation of the scanner. ConclusionsThe fan-beam energy and air kerma distributions of CT scanners can be effectively measured using this pin-photodiode array.

Design and development of a dedicated portable gamma camera system for intra-operative imaging

PurposeWe developed a high performance portable gamma camera platform dedicated to identification of sentinel lymph nodes (SLNs) and radio-guided surgery for cancer patients. In this work, we present the performance characteristics of SURGEOSIGHT-I, the first version of this platform that can intra-operatively provide high-resolution images of the surveyed areas. MethodsAt the heart of this camera, there is a 43×43 array of pixelated sodium-activated cesium iodide (CsI(Na)) scintillation crystal with 1×1mm2 pixel size and 5mm thickness coupled to a Hamamatsu H8500 flat-panel multi-anode (64 channels) photomultiplier tube. The probe is equipped with a hexagonal parallel-hole lead collimator with 1.2mm holes. The detector, collimator, and the associated front-end electronics are encapsulated in a common housing referred to as head. ResultsOur results show a count rate of ∼41kcps for 20% count loss. The extrinsic energy resolution was measured as 20.6% at 140keV. The spatial resolution and the sensitivity of the system on the collimator surface was measured as 2.2mm and 142cps/MBq, respectively. In addition, the integral and differential uniformity, after uniformity correction, in useful field-of-view (UFOV) were measured 4.5% and 4.6%, respectively. ConclusionsThis system can be used for a number of clinical applications including SLN biopsy and radiopharmaceutical-guided surgery.

Detection of a gas region in a human body across a therapeutic carbon beam by measuring low-energy photons

We studied feasibility of detection of a gap which is located across a beam track by measuring low-energy (63–68 keV) photons generated by beam irradiation. An experiment was performed with the Heavy Ion Medical Accelerator in Chiba (HIMAC). A 12C beam having 290 MeV/u was injected on a target consisting of two acrylic blocks. These two blocks were placed with a 10 mm gap along the beam axis. A detection system consisting of a semiconductor detector, a lead collimator having a slit, and borated polyethylene blocks was placed on a movable stage to detect low-energy photons emitted perpendicularly to the beam axis. The position of the detection system was moved at 2 mm intervals along the beam axis. It was found that the yield of 63–68 keV photons was clearly correlated with the position of the detection system. The position at which the yield curve had the lowest value agreed with the gap position. We also confirmed that the experimental result was well reproduced by a Monte Carlo simulation that includes generation of secondary electron bremsstrahlung.

A Study of Thyroid 131I Activity of Five Human Subjects Exposed to a Radioactive Plume at Tamura City in Fukushima.

Thyroid 131I activities were determined for five human subjects from a disaster medical assistance team of Fukui Prefectural Hospital. The team was dispatched to the Tamura City Sports Park, 40 km from the Fukushima Daiichi nuclear power plant. They were exposed to a radioactive plume on 15 March 2011. In vivo measurements at Fukui Prefectural Hospital were conducted around 17 h after the team left the park. A thyroid counter equipped with a 51-mm-diameter × 51-mm-thick NaI(Tl) detector with a 20-mm-thick lead collimator was used. Mock iodine (133Ba and 137Cs) with a thyroid uptake neck phantom was used for calibration. On 16 March 2011, at 11:30, thyroid activity of a member of the team age 53 y, who was never administered stable iodine, was 268 ± 38 Bq. The remaining four men, aged 49, 35, 34, and 27 y, ingested two stable iodine pills (a total of 100 mg of potassium iodide) approximately 36 h before being exposed to the plume. Their thyroid activity values were 249 ± 86 Bq, 676 ± 107 Bq, 569 ± 96 Bq, and 1,082 ± 119 Bq, respectively. An inverse relationship between age and thyroid activity was observed among those who ingested potassium iodide before exposure, indicating that stable iodine administration may have a protective effect. Thyroid 131I activity was reduced by approximately 70% in the oldest person. This can be explained by the iodine metabolism in the thyroid of younger individuals being significantly faster than that of older individuals.

Industrial tomography using three different gamma ray

This study describes the development of a multisource computed tomography (CT) system that proved to be a useful tool to study multiphase systems. In this CT system, two different radioisotope sources, 192Ir (317keV and 448keV) and 137Cs (662keV), were placed in a single lead collimator and several tomography measurements carried out. The multisource CT system was capable of determining as well as differentiating the attenuation coefficients of materials with two phases (gas and liquid). It was also able to provide important information concerning the hydrodynamics occurring inside a multiphase column.

Measurement of the point spread function of a pixelated detector array.

In order to further understand the PET/MRI scanner of our group, we measured the point spread function of a preclinical scintillation crystal array with a pitch of 1 mm and a total size of 30 mm ~ 30 mm ~ 12 mm. It is coupled via a lightguide to a dSiPM from Philips Digital Photon Counting, used on the TEK-setup. Crystal identification is done with a centre of gravity algorithm and the whole data analysis is performed with the same processing software as for the PET insert, giving comparable results. The beam is created with a 22 NA-Point-Source and a lead collimator, with 0.5 mm bore diameter. The algorithm sorted 62 % of the coincidences into the correct crystal.

Ion-induced gamma-ray detection of fast ions escaping from fusion plasmas.

A 12 × 12 pixel detector has been developed and used in a laboratory experiment for lost fast-ion diagnostics. With gamma rays in the MeV range originating from nuclear reactions (9)Be(α, nγ)(12)C, (9)Be(d, nγ)(12)C, and (12)C(d, pγ)(13)C, a high purity germanium (HPGe) detector measured a fine-energy-resolved spectrum of gamma rays. The HPGe detector enables the survey of background-gamma rays and Doppler-shifted photo peak shapes. In the experiments, the pixel detector produces a gamma-ray image reconstructed from the energy spectrum obtained from total photon counts of irradiation passing through the detector's lead collimator. From gamma-ray image, diagnostics are able to produce an analysis of the fast ion loss onto the first wall in principle.

WE‐D‐BRF‐03: Proton Beam Range Verification with a Single Prompt Gamma‐Ray Detector

Purpose:To present an experimental study of a novel range verification method for scanned and scattered proton beams.Methods:A detection system consisting of an actively shielded lanthanum(III)bromide scintillator and a one‐sided lead collimator was used to measure prompt gamma‐rays emitted during the delivery of proton beams to a water phantom and an anthropomorphic head phantom. The residual proton range at the collimator position was determined by comparing gamma‐ray intensities while the proton energy was modulated to the distal end of the target. We used a clinical field to deliver a 50 cGy dose to a 12 cm diameter target in the water phantom and to a 175 cc tumor‐shaped target in the head phantom. The detector signals were acquired with a custom data acquisition system enabling energy and time‐of‐flight discrimination of prompt gamma‐rays.Results:Range deviations were detected with a statistical accuracy of ± 0.2 mm and ± 1.4 mm at 90% confidence level, respectively for the water and head phantom. We obtained a time resolution of 1 ns FWHM and an energy resolution < 2% FWHM for the main gamma lines from proton‐induced nuclear reactions with carbon and oxygen. This allowed for an accurate separation of the prompt gamma‐rays from neutron‐induced background.Conclusion:Proton range deviations can be detected with millimeter accuracy using a single prompt gamma‐ray measurement point acquired during the delivery of a few proton energy layers to the distal part of the target. The method is also feasible in the presence of background radiation from passively scattered proton beam delivery.

診断領域における散乱X線含有率のコリメータを用いた間接測定法

The lead disc method is conventionally applied to measure the scatter fraction directly in the energy range of diagnostic X-rays. There are numerous reports of use of this method, but it is difficult to make lead discs with sufficient fabrication accuracy. In this paper, we newly propose an indirect measurement method using collimators instead. In our method, we measure the following two experimental values: the sum of the intensities of the direct X-rays and scattered X-rays, and the intensity of direct X-rays using lead collimators. The ratio of these two values shows the fraction of the direct X-ray that is the complementary value of the scatter fraction. To verify this method experimentally, we carried out experiments using a computed radiography system at tube voltages of 40 kV to 100 kV, and phantom thicknesses of 10 mm to 100 mm. The results confirmed the validity of our method.

Monte Carlo simulation of GM probe and NaI detector efficiency for surface activity measurements

This paper deals with the direct measurement of total (fixed plus removable) surface activity in the presence of interfering radiation fields. Two methods based on Monte Carlo simulations are used: one for a Geiger–Muller (GM) ionisation probe and the other for sodium iodide (NaI) detector with lead collimators; equations for the most general case and the geometry models for Monte Carlo simulation of both (GM and NaI) detectors are employed. Finally, an example of application is discussed.

Experimental demonstration of direct L ‐shell x‐ray fluorescence imaging of gold nanoparticles using a benchtop x‐ray source

To develop a proof-of-principle L-shell x-ray fluorescence (XRF) imaging system that locates and quantifies sparse concentrations of gold nanoparticles (GNPs) using a benchtop polychromatic x-ray source and a silicon (Si)-PIN diode x-ray detector system. 12-mm-diameter water-filled cylindrical tubes with GNP concentrations of 20, 10, 5, 0.5, 0.05, 0.005, and 0 mg∕cm3 served as calibration phantoms. An imaging phantom was created using the same cylindrical tube but filled with tissue-equivalent gel containing structures mimicking a GNP-loaded blood vessel and approximately 1 cm3 tumor. Phantoms were irradiated by a 3-mm-diameter pencil-beam of 62 kVp x-rays filtered by 1 mm aluminum. Fluorescence∕scatter photons from phantoms were detected at 90° with respect to the beam direction using a Si-PIN detector placed behind a 2.5-mm-diameter lead collimator. The imaging phantom was translated horizontally and vertically in 0.3-mm steps to image a 6 mm×15 mm region of interest (ROI). For each phantom, the net L-shell XRF signal from GNPs was extracted from background, and then corrected for detection efficiency and in-phantom attenuation using a fluorescence-to-scatter normalization algorithm. XRF measurements with calibration phantoms provided a calibration curve showing a linear relationship between corrected XRF signal and GNP mass per imaged voxel. Using the calibration curve, the detection limit (at the 95% confidence level) of the current experimental setup was estimated to be a GNP mass of 0.35 μg per imaged voxel (1.73×10(-2) cm3). A 2D XRF map of the ROI was also successfully generated, reasonably matching the known spatial distribution as well as showing the local variation of GNP concentrations. L-shell XRF imaging can be a highly sensitive tool that has the capability of simultaneously imaging the spatial distribution and determining the local concentration of GNPs presented on the order of parts-per-million level within subcentimeter-sized ex vivo samples and superficial tumors during preclinical animal studies.

Development of a pinhole gamma camera for environmental monitoring

The collimator design for a nuclear monitoring system should be considered differently from the collimator design for medical environments because it has to be used in high-energy radiation environments. The purpose of this study was to determine the optimum pinhole design and to evaluate its performance for acquiring good-quality image in a high-energy radiation field. Simulations using the Geant4 Application for Tomographic Emission (GATE) were performed to model the pinhole gamma camera system. The gamma camera consists of a pyramid-shaped lead collimator with a tungsten pinhole insert, and a CsI(Tl) scintillation crystal with thickness of 6.0 mm and area of 50.0 mm × 50.0 mm. The acceptance angle of the pinhole collimator and the distance from pinhole to scintillator crystal were set to 45° and 60 mm, respectively. The intrinsic spatial resolution and sensitivity were simulated by changing the pinhole diameter and channel height. The point source was located 60 mm above the center of the pinhole, and the transmitted image was estimated for pinhole diameter values from 2.0 mm to 4.0 mm, while the channel heights were fixed between 2.0 mm and 6.0 mm. The optimal ranges of channel height and pinhole diameter were determined by evaluating the intrinsic resolution and sensitivity tradeoff curves. The pinhole parameters were selected based on these analyses, and we verified the simulation results through experimental tests of three types of collimators (general purpose, high sensitivity, and high resolution). The simulated and experimental results agreed, with discrepancies of 4.5% and 6.4% in the sensitivity and spatial resolution, respectively. The results demonstrate that the pinhole collimator designed in this study could be utilized to perform radiation monitoring.

A system of materials composition and geometry arrangement for fast neutron beam thermalization: An MCNP study

Compact deuterium–tritium neutron generators emit fast neutrons (14.2MeV) that have to be thermalized for neutron activation analysis experiments. To maximize thermal neutron flux and minimize epithermal and fast neutron fluxes across the output surface of the neutron generator facility, Monte Carlo calculations (MCNP5; Los Alamos National Laboratory) for different moderator types and widths and collimator and reflector designs have been performed. A thin lead layer close to the neutron generator as neutron multiplier followed by polyethylene moderator and surrounded by a massive lead and nickel collimator and reflector was obtained as the optimum setup.

Measurements of Fission and Radioactive Capture Reaction Rates Inside the Fuel of the Ipen/MB-01

This work presents the measures of the nuclear reaction rates along the radial direction of the fuel pellet by irradiation and posterior gamma spectrometry of a thin slice of fuel pellet of UO2 at 4.3% enrichment. From its irradiation, the rate of radioactive capture and fission had been measured as a function of the radius of the pellet disk using a Ortec GMX HPGe detector. Lead collimators had been used for this purpose. Simulating the fuel pellet in the pin fuel of the IPEN/MB-01 reactor, a thin UO2 disk is used, being inserted in the interior of a dismountable fuel rod. This fuel rod is then placed in the central position of the IPEN/MB-01 reactor core and irradiated during 1 h under a neutron flux of 5 ×108 n/cm2 s. In gamma spectrometry, 10 collimators with different diameters have been used; consequently, the nuclear reactions of radioactive capture that occurs in atoms of 238U and the fission that occurs on both 235U and 238U are measured in function of 10 different regions (diameter of collimator) of the UO2 fuel pellet disk. Nuclear fission produces different fission products such as 143Ce with a yield fission of 5.9% which decay is monitored in this work. Corrections in geometric efficiency due to introduction of collimators on HPGe detection system were estimated using photon transport of MCNP-4C code. Some calculated values of nuclear reaction rate of radioactive capture and fission along the radial direction of the fuel pellet obtained by Monte Carlo methodology, using the MCNP-4C code, are presented and compared to the experimental data showing very good agreement.

Measuring whole‐body neutrophil redistribution using a dedicated whole‐body counter and ultra‐low doses of 111Indium

There is increasing interest in the 'homing' of neutrophils to bone marrow. The aim of this study was to measure the whole-body redistribution of (111) In using a whole-body counter following the administration of ultra-small activities of (111) In-labelled neutrophils. The detectors of a dedicated whole-body counter were fitted with lead collimators. Whole-body (111) In distribution was recorded at 45 min, 24 h, and 2, 4, 7 and 10 days after administration of (111) In-labelled neutrophils (0·29-0·74 MBq) in eight healthy non-smokers, five healthy smokers, eight patients with inactive bronchiectasis, three with asthma and nine with chronic obstructive pulmonary disease (COPD). Intravascular 45-min (111) In-labelled neutrophil recovery was not significantly different between groups, ranging from 33 (SD 8%) in healthy smokers to 45 (14%) in healthy non-smokers (P > 0·05). Peaks were identified on the whole body count profile corresponding to the chest, upper abdomen (liver/spleen) and pelvis (bone marrow). (111) In distribution changed between 45 min and 24 h and then remained stable thereafter. Peak chest counts increased ∼ 1·5-fold between 45 min and 24 h, whereas upper abdominal peak counts decreased by ∼ 25% with no significant inter-group differences. The increment in pelvic counts (∼ 2·7-fold) was similar between groups, except COPD patients, in whom it was 2·04 (0·35; P < 0·02 vs. healthy participants). Assuming neutrophils are distributed only between blood, liver, spleen and bone marrow, the data suggest that marrow pools 25% and destroys 67% of circulating neutrophils, rising in COPD to 40% and 80%, respectively, possibly as a result of the effects on marrow of chronic hypoxaemia.

Design and dosimetry characteristics of a commercial applicator system for intra‐operative electron beam therapy utilizing ELEKTA Precise accelerator

The design concept and dosimetric characteristics of a new applicator system for intraoperative radiation therapy (IORT) are presented in this work. A new hard‐docking commercial system includes polymethylmethacrylate (PMMA) applicators with different diameters and applicator end angles and a set of secondary lead collimators. A telescopic device allows changing of source‐to‐surface distance (SSD). All measurements were performed for 6, 9, 12 and 18 MeV electron energies. Output factors and percentage depth doses (PDD) were measured in a water phantom using a plane‐parallel ion chamber. Isodose contours and radiation leakage were measured using a solid water phantom and radiographic films. The dependence of PDD on SSD was checked for the applicators with the smallest and the biggest diameters. SSD dependence of the output factors was measured. Hardcopies of PDD and isodose contours were prepared to help the team during the procedure on deciding applicator size and energy to be chosen. Applicator output factors are a function of energy, applicator size and applicator type. Dependence of SSD correction factors on applicator size and applicator type was found to be weak. The same SSD correction will be applied for all applicators in use for each energy. The radiation leakage through the applicators is clinically acceptable. The applicator system enables effective collimation of electron beams for IORT. The data presented are sufficient for applicator, energy and monitor unit selection for IORT treatment of a patient.PACS number: 87.00.00, 29.20.‐c