Energy Collimator Research Articles

Optimisation of scintigraphic imaging of the novel therapeutic agent Ra-223 in the treatment of metastatic castration resistant prostate cancer

Introduction Imaging of radionuclide therapy agents is useful in determining biodistribution, verification of correct pharmaceutical and to rule out extravasation in clinical administrations. The aim of this study was to optimise imaging of Ra-223 dichloride (Xofigo™) for patients with metastatic castration resistant prostate cancer. Materials and methods A Jaszczak phantom and bar resolution phantom were used with 0.8 MBq of Ra-223 to evaluate image quality for a range of collimators, energy windows and matrices for planar and SPECT imaging (Siemens ECam, Erlangen). Clinical imaging was carried out twenty minutes post injection of Ra-223. Four sets of static images were obtained on two patients undergoing treatment, pre and post optimisation. Results Optimum imaging parameters were found using planar imaging with a Xenon-133 energy window (80 kV photopeak, 20% energy window), 128 × 128 matrix. A medium energy collimator resulted in higher resolution images with reduced image noise compared to a low energy general purpose collimator. These parameters allowed for clinically acceptable image quality with an imaging time acceptable for patient comfort (20 min). Clinical imaging allowed visualisation of structures post administration of Ra-223. Post optimisation images were of better quality although pre and post optimisation images were clinically useful. Conclusion Useful clinical information can be obtained from scintigraphic imaging of Ra-223. The quality of imaging improved with optimisation of imaging parameters.

Metamaterial-based lossy anisotropic epsilon-near-zero medium for energy collimation

A lossy anisotropic epsilon-near-zero (ENZ) medium may lead to a counterintuitive phenomenon of omnidirectional bending-to-normal refraction [S. Feng, Phys. Rev. Lett. 108, 193904 (2012)], which offers a fabulous strategy for energy collimation and energy harvesting. Here, in the scope of effective medium theory, we systematically investigate two simple metamaterial configurations, i.e., metal-dielectric-layered structures and the wire medium, to explore the possibility of fulfilling the conditions of such an anisotropic lossy ENZ medium by playing with materials' parameters. Both realistic metamaterial structures and their effective medium equivalences have been numerically simulated, and the results are in excellent agreement with each other. Our study provides clear guidance and therefore paves the way towards the search for proper designs of anisotropic metamaterials for a decent effect of energy collimation and wave-front manipulation.

SU‐G‐IeP4‐12: Performance of In‐111 Coincident Gamma‐Ray Counting: A Monte Carlo Simulation

Purpose:The decay of In‐111 results in a non‐isotropic gamma‐ray cascade, which is normally imaged using a gamma camera. Creating images with a gamma camera using coincident gamma‐rays from In‐111 has not been previously studied. Our objective was to explore the feasibility of imaging this cascade as coincidence events and to determine the optimal timing resolution and source activity using Monte Carlo simulations.Methods:GEANT4 was used to simulate the decay of the In‐111 nucleus and to model the gamma camera. Each photon emission was assigned a timestamp, and the time delay and angular separation for the second gamma‐ray in the cascade was consistent with the known intermediate state half‐life of 85ns. The gamma‐rays are transported through a model of a Siemens dual head Symbia “S” gamma camera with a 5/8‐inch thick crystal and medium energy collimators. A true coincident event was defined as a single 171keV gamma‐ray followed by a single 245keV gamma‐ray within a specified time window (or vice versa). Several source activities (ranging from 10uCi to 5mCi) with and without incorporation of background counts were then simulated. Each simulation was analyzed using varying time windows to assess random events. The noise equivalent count rate (NECR) was computed based on the number of true and random counts for each combination of activity and time window. No scatter events were assumed since sources were simulated in air.Results:As expected, increasing the timing window increased the total number of observed coincidences albeit at the expense of true coincidences. A timing window range of 200–500ns maximizes the NECR at clinically‐used source activities. The background rate did not significantly alter the maximum NECR.Conclusion:This work suggests coincident measurements of In‐111 gamma‐ray decay can be performed with commercial gamma cameras at clinically‐relevant activities. Work is ongoing to assess useful clinical applications.

The Effect of Parallel-hole Collimator Material on Image and Functional Parameters in SPECT Imaging: A SIMIND Monte Carlo Study.

The collimator in single-photon emission computed tomography (SPECT) is a critical component of the imaging system and plays an impressive role in the imaging quality. In this study, the effect of the collimator material on the radioisotopic image and its functional parameters was studied. The simulating medical imaging nuclear detectors (SIMIND) Monte Carlo program was used to simulate a Siemens E.CAM SPECT (Siemens Medical Solutions, Erlangen, Germany) system equipped with a low-energy high-resolution (LEHR) collimator. The simulation and experimental data from the SPECT imaging modality using 99mTc were obtained on a point source and Jaszczak phantom. Seventeen high atomic number materials were considered as LEHR collimator materials. In order to determine the effect of the collimator material on the image and functional parameters, the energy resolution, spatial resolution, contrast, and collimator characteristics parameters such as septal penetration and scatter-to-primary ratio were investigated. Energy spectra profiles, full width at half maximums (FWHMs) (mm) of the point spread function (PSF) curves, system sensitivity, and contrast of cold spheres of the Jaszczak phantom for the simulated and experiment systems have acceptability superimposed. The results of FWHM and energy resolution for the 17 collimators showed that the collimator made of 98% lead and 2% antimony could provide the best FWHM and energy resolution, 7.68 mm and 9.87%, respectively. The LEHR collimator with 98% lead and 2% antimony offers the best resolution and contrast when compared to other high atomic number metals and alloys.

Search for patterns by combining cosmic-ray energy and arrival directions at the Pierre Auger Observatory.

Energy-dependent patterns in the arrival directions of cosmic rays are searched for using data of the Pierre Auger Observatory. We investigate local regions around the highest-energy cosmic rays with E ge 6 times 10^{19} eV by analyzing cosmic rays with energies above E ge 5 times 10^{18} eV arriving within an angular separation of approximately 15^{circ }. We characterize the energy distributions inside these regions by two independent methods, one searching for angular dependence of energy-energy correlations and one searching for collimation of energy along the local system of principal axes of the energy distribution. No significant patterns are found with this analysis. The comparison of these measurements with astrophysical scenarios can therefore be used to obtain constraints on related model parameters such as strength of cosmic-ray deflection and density of point sources.

SU-C-201-05: Imaging 212Pb-TCMC-Trastuzumab for Alpha Radioimmunotherapy for Ovarian Cancer

Purpose: To support the phase I trial for toxicity, biodistribution and pharmacokinetics of intra-peritoneal (IP) 212Pb-TCMC-trastuzumab in patients with HER-2 expressing malignancy. A whole body gamma camera imaging method was developed for estimating amount of 212Pb-TCMC-trastuzumab left in the peritoneal cavity. Methods: 212Pb decays to 212Bi via beta emission. 212Bi emits an alpha particle at an average of 6.1 MeV. The 238.6 keV gamma ray with a 43.6% yield can be exploited for imaging. Initial phantom was made of saline bags with 212Pb. Images were collected for 238.6 keV with a medium energy general purpose collimator. There are other high energy gamma emissions (e.g. 511keV, 8%; 583 keV, 31%) that penetrate the septae of the collimator and contribute scatter into 238.6 keV. An upper scatter window was used for scatter correction for these high energy gammas. Results: A small source containing 212Pb can be easily visualized. Scatter correction on images of a small 212Pb source resulted in a ∼50% reduction in the full width at tenth maximum (FWTM), while change in full width at half maximum (FWHM) was <10%. For photopeak images, substantial scatter around phantom source extended to > 5 cm outside; scatter correction improved image contrast by removing this scatter around the sources. Patient imaging, in the 1st cohort (n=3) showed little redistribution of 212Pb-TCMC-trastuzumab out of the peritoneal cavity. Compared to the early post-treatment images, the 18-hour post-injection images illustrated the shift to more uniform anterior/posterior abdominal distribution and the loss of intensity due to radioactive decay. Conclusion: Use of medium energy collimator, 15% width of 238.6 keV photopeak, and a 7.5% upper scatter window is adequate for quantification of 212Pb radioactivity inside peritoneal cavity for alpha radioimmunotherapy of ovarian cancer. Research Support: AREVA Med, NIH 1UL1RR025777-01

External beam’s nozzle design for the CRC cyclotron PIXE/PIGE

Recently, 13-MeV proton cyclotrons have been applied to non-destructive trace element analytical techniques, such as proton-induced X-ray emission (PIXE) and proton-induced gamma-ray emission (PIGE). A new extended beam line has been designed for PIXE/PIGE measurements in order to deliver protons to the target with minimal losses, thus reducing secondary radiation. A target chamber for PIXE/PIGE measurements is installed at the end of the extended beam line, and the beam size may be optimized by using a series of collimators that are located in front of the target. The optimized proton beam, with low currents (∼nA) for PIXE/PIGE experiments, requires a small beam size with variable energies from ∼10 keV to 3 MeV. Based on the ionization cross-section curve, a 3-MeV proton beam has been determined to be suitable for PIXE/PIGE measurements. Therefore, the 13-MeV protons extracted from the cyclotron must be reduced to 3 MeV, and this is achieved through the incorporation of an energy degrader. The appropriate thickness of the energy degrader has been estimated by using the stopping range in matter (SRIM) program. Also, suitable materials must be used for the construction of the collimator and the energy degrader in order to meet the requirements of low neutron activation due to the application of protons. In this study, we evaluated a number of suitable materials with low neutron yields and with little energy spread as the beam passes through the energy degrader and collimator. The appropriate thickness of the energy degrader for the reduction of the proton energy from 13 MeV to 3 MeV was determined using the SRIM code. Also, the neutron yield at the nozzle was estimated using the MCNPX code.

Current gain in sub-10 nm base GaN tunneling hot electron transistors with AlN emitter barrier

We report on Gallium Nitride-based tunneling hot electron transistor amplifier with common-emitter current gain greater than 1. Small signal current gain up to 5 and dc current gain of 1.3 were attained in common-emitter configuration with collector current density in excess of 50 kA/cm2. The use of a combination of 1 nm GaN/3 nm AlN layers as an emitter tunneling barrier was found to improve the energy collimation of the injected electrons. These results represent demonstration of unipolar vertical transistors in the III-nitride system that can potentially lead to higher frequency and power microwave devices.

Experimental assessment of peripheral dose in high-energy electron beams used in external radiotherapy

Peripheral dose from bremsstrahlung and scattered electrons in high-energy electron beams in external radiotherapy remains poorly studied. The purpose of this work is to assess peripheral dose outside applicators at the patient level. Commissioning was performed for 6, 9, 12 and 18 MeV electron beams on three linear accelerators Varian 2300 C/D (Varian applicator), Siemens Primus KD2 (Deva applicator) and Siemens Oncor (applicator EA3). The peripheral dose was measured in a water phantom as a function of off-axis distance from 5 cm to 65 cm from the field edge for SSD = 100 cm. Thermoluminescent TLD-700 powder dosimeters were used. Measurements were made at both 1 cm and 10 cm depths, using applicator sizes from 6 × 6cm 2 to 20 × 20 cm 2 , the results assuming that the TLD signal is proportional to the dose. Whatever the field size, a peak dose spot appeared at 15 cm from the field edge for Siemens applicators. For Siemens Primus with an applicator size of 10 × 10 cm 2 , this peak reached 2,1%, 1%, 0,9% and 1,3% of Dmax for 6, 9, 12 and 18 MeV electron beams, respectively, doubled for 6 × 6 cm 2 field size. For Siemens Oncor, with the above applicator size, this peak dose reached 0,8%, 1,2% and 1,3% of Dmax for 6, 9 and 12MeV, respectively, doubled for 20 × 20cm 2 . In contrast for Varian 2300 C/D, the doses at 15 cm from field edge were 0,3%, 0,6% and 1,1% of Dmax for 6,12 and 18 MeV, respectively. No peak dose spot was evidenced for Varian applicator. The doses measured at 10 cm depth were 2–3 times lower than doses at 1 cm depth for out off- field distances from 5 cm to 35 cm, and were 4–7 times lower for larger distances. This work analyzes peripheral doses for different electron beams energies and three different applicator types. It shows that depending on beam energy, applicator size and type, the peak dose at 15 cm from field edge ranges from 0,3–2,7% of the Dmax. Measurements made at 10 cm depth show that, depending on beam energy and applicator size and collimator size, the dose at 15 cm from field edge is 0,07–0,2% of Dmax. Although the debate on signal to dose conversion coefficients for mixed fields is still ongoing, our results should be considered because, to date, peripheral dose with electron beams are not fully accounted for by TPS.

In-medium jet shape from energy collimation in parton showers: Comparison with CMS PbPb data at 2.76 TeV

We present the medium-modified energy collimation in the leading-logarithmic approximation (LLA) and next-to-leading-logarithmic approximation (NLLA) of QCD. As a consequence of more accurate kinematic considerations in the argument of the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) fragmentation functions (FFs) we find a new NLLA correction $\mathcal{O}({\ensuremath{\alpha}}_{s})$ which accounts for the scaling violation of DGLAP FFs at small $x$. The jet shape is derived from the energy collimation within the same approximations and we also compare our calculations for the energy collimation with the event generators pythia6 and YaJEM for the first time in this paper. The modification of jets by the medium in both cases is implemented by altering the infrared sector using the Borghini-Wiedemann model. The energy collimation and jet shapes qualitatively describe a clear broadening of showers in the medium, which is further supported by YaJEM in the final comparison of the jet shape with CMS PbPb data at center-of-mass energy 2.76 TeV. The comparison of the biased versus unbiased YaJEM jet shape with the CMS data shows a more accurate agreement for biased showers and illustrates the importance of an accurate simulation of the experimental jet-finding strategy.

Impact of a predefined mediastinal ROI on inter-observer variability of planar 123I-MIBG heart-to-mediastinum ratio

AimPurpose of this study was to assess the impact of mediastinal region of interest (ROI) definition on intra- and inter-observer variability in relation to collimator type. MethodsThirty-five subjects with CHF (80% men, mean age 66 ± 9 years, NYHA 2.4 ± 0.5, LVEF 29 ± 8.4%) were enrolled. 15 minutes and 4 hours post-injection (p.i.) of 123I-MIBG, planar images were sequentially acquired with low energy high energy (LEHR) and medium energy (ME) collimators. In the first analysis, observer-defined mediastinal ROI was used. In the second analysis, a predefined mediastinal ROI was used. Intra- and inter-observer variability of late H/M was assessed using Lin’s concordance coefficient (LCC). ResultsThere was substantial agreement between all three observers using predefined mediastinum ROI. LCCs for LEHR were 0.98, 0.96, and 0.95, for ME 0.98, 0.97, and 0.97. However, observer-defined mediastinal ROI resulted in poor-moderate agreement. LCCs for LEHR were 0.82, 0.94, and 0.70, for ME 0.77, 0.91, and 0.80. Intra-observer analysis using predefined mediastinal ROI showed substantial agreement. LCC was 0.97 for LEHR and 0.96 for ME. ConclusionPredefined mediastinal ROI results in low intra- and inter-observer variability of late H/M and is, therefore, to be preferred over observer-defined mediastinal ROI. Intra- and inter-observer variability of late H/M is not influenced by collimator choice.

An experimental comparison of two different technetium source activities which can imitate thyroid scintigraphy in case of thyroid toxic nodule.

Purpose:In cases of thyroid toxic autonomous nodule, anterior projection of Tc-99m pertechnetate image shows a hot nodule that occupies most, or the entire thyroid lobe with near-total or total suppression of the contra lateral lobe. In this case is very difficult to distinguish toxic nodule from lobe agenesis. Our interest was to estimate and determinate the rate of radioactivity when the source with high activity can make total suppression of the second source with low activity in same conditions with thyroid scintigraphy procedures.Material and methodology:Thyroid scintigraphy was performed with Technetium 99 meta stable pertechnetate. A parallel high resolution low energy collimator was used as an energy setting of 140 KeV photo peak for T-99m. Images are acquired at 200 Kilo Counts in the anterior projection with the collimator positioned as close as the patient’s extended neck (approximately in distance of 18 cm). The scintigraphy of thyroid gland was performed 15 minutes after intravenous administration of 1.5 mCi Tc-99m pertechnetate. Technetium 99 meta stable radioactive sources with different activity were used for two scintigraphies studies, performed in same thyroid scintigraphy acquisition procedures. In the first study, were compared the standard source with high activity A=11.2 mCi with sources with variable activities B=1.33 mCi; 1.03 mCi; 0.7 mCi; 0.36 mCi; and 0.16mCi) in distance of 1.5cm from each other sources, which is approximately same with distance between two thyroid lobes. In the second study were compared the sources with low activity in proportion 70:1(source A = 1.5 mCi and source B=0.021mCi). As clinical studies we preferred two different patents with different thyroid disorders. There were one patient with thyroid toxic nodule in the right lobe, therefore the second patient was with left thyroid nodule agenesis.Results:During our examination, we accurately determined that two radioactive sources in proportion 70:1 will be displayed as only one source with complete suppression of other source with low radioactivity. Also we found that covering of toxic nodules with lead cover (plaque), can allow visualization of activity in suppressed lobe.Conclusion:Our study concluded that total lobe suppression, in cases of patients with thyroid toxic nodule, will happened for sure, if toxic nodule had accumulated seventy times more radioactivity than normal lobe. Also we concluded that covering of the toxic nodule with lead plaque, may permit the presentation of radioactivity in suppressed nodule.

Short-Duration Gamma-Ray Bursts

Gamma-ray bursts (GRBs) display a bimodal duration distribution with a separation between the short- and long-duration bursts at about 2 s. The progenitors of long GRBs have been identified as massive stars based on their association with Type Ic core-collapse supernovae (SNe), their exclusive location in star-forming galaxies, and their strong correlation with bright UV regions within their host galaxies. Short GRBs have long been suspected on theoretical grounds to arise from compact object binary mergers (neutron star–neutron star or neutron star–black hole). The discovery of short GRB afterglows in 2005 provided the first insight into their energy scale and environments, as well as established a cosmological origin, a mix of host-galaxy types, and an absence of associated SNe. In this review, I summarize nearly a decade of short GRB afterglow and host-galaxy observations and use this information to shed light on the nature and properties of their progenitors, the energy scale and collimation of the relativistic outflow, and the properties of the circumburst environments. The preponderance of the evidence points to compact object binary progenitors, although some open questions remain. On the basis of this association, observations of short GRBs and their afterglows can shed light on the on- and off-axis electromagnetic counterparts of gravitational wave sources from the Advanced LIGO/Virgo experiments.

Nonlinear protection of beam delivery systems for multi-TeV linear colliders

The post-linac energy collimation system of future e+e− multi-TeV linear colliders is designed to fulfil an essential function of protection of the Beam Delivery System (BDS) against miss-steered or errant beams likely generated by failure modes in the main linac. For the case of the Compact Linear Collider (CLIC), the energy collimators are required to withstand the impact of a full bunch train in case of failure. This condition makes the design of the energy collimation system especially challenging, if we take into account the need to dispose of an unprecedented transverse beam energy density per beam of the order of GJ/mm2, when assuming the nominal CLIC beam parameters at 3 TeV centre-of-mass energy, which translates into an extremely high damage potential of uncontrolled beams. This leads to research activities involving new collimator materials and novel collimation techniques. The increase of the transverse spot size at the collimators using nonlinear magnets is a potential solution to guarantee the survival of the collimators. In this paper we present an alternative nonlinear optics based on a multipole magnet pair for energy collimation. In order to preserve an acceptable luminosity performance, we carefully study the general conditions for self-cancellation of optical aberrations between two multipoles. This nonlinear optics scheme is adapted to the requirements of the post-linac energy collimation system for the CLIC BDS, and its performance is investigated by means of beam tracking simulations. Although applied to the CLIC case, this nonlinear protection system could be adapted to other future colliders.

Collimation of energy in medium-modified QCD jets

The collimation of energy inside medium-modified jets is investigated in the leading logarithmic approximation of QCD. The Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) evolution equations are slightly modified by introducing splitting functions enhanced in the infrared sector. As compared to elementary collisions in the vacuum, the angular distribution of the jet energy is found to broaden in QCD media.

Monte Carlo simulations of adult and pediatric computed tomography exams: Validation studies of organ doses with physical phantoms

To validate the accuracy of a Monte Carlo source model of the Siemens SOMATOM Sensation 16 CT scanner using organ doses measured in physical anthropomorphic phantoms. The x-ray output of the Siemens SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carlo radiation transport code, MCNPX version 2.6. The resulting source model was able to perform various simulated axial and helical computed tomographic (CT) scans of varying scan parameters, including beam energy, filtration, pitch, and beam collimation. Two custom-built anthropomorphic phantoms were used to take dose measurements on the CT scanner: an adult male and a 9-month-old. The adult male is a physical replica of the University of Florida reference adult male hybrid computational phantom, while the 9-month-old is a replica of the University of Florida Series B 9-month-old voxel computational phantom. Each phantom underwent a series of axial and helical CT scans, during which organ doses were measured using fiber-optic coupled plastic scintillator dosimeters developed at the University of Florida. The physical setup was reproduced and simulated in MCNPX using the CT source model and the computational phantoms upon which the anthropomorphic phantoms were constructed. Average organ doses were then calculated based upon these MCNPX results. For all CT scans, good agreement was seen between measured and simulated organ doses. For the adult male, the percent differences were within 16% for axial scans, and within 18% for helical scans. For the 9-month-old, the percent differences were all within 15% for both the axial and helical scans. These results are comparable to previously published validation studies using GE scanners and commercially available anthropomorphic phantoms. Overall results of this study show that the Monte Carlo source model can be used to accurately and reliably calculate organ doses for patients undergoing a variety of axial or helical CT examinations on the Siemens SOMATOM Sensation 16 scanner.

Assessment of leakage doses around the treatment heads of different linear accelerators

Out-of-field doses to untargeted organs may have long-term detrimental health effects for patients treated with radiotherapy. It has been observed that equivalent treatments delivered to patients with different accelerators may result in significant differences in the out-of-field dose. In this work, the points of leakage dose are identified about the gantry of several treatment units. The origin of the observed higher doses is investigated. LiF:Mg,Cu,P thermoluminescent dosimetry has been employed to quantify the dose at a several points around the linac head of various linear accelerators (linacs): a Varian 600C, Varian 21-iX, Siemens Primus and Elekta Synergy-II. Comparisons are also made between different energy modes, collimator rotations and field sizes. Significant differences in leaked photon doses were identified when comparing the various linac models. The isocentric-waveguide 600C generally exhibits the lowest leakage directed towards the patient. The Siemens and Elekta models generally produce a greater leakage than the Varian models. The leakage 'hotspots' are evident on the gantry section housing the waveguide on the 21-iX. For all machines, there are significant differences in the x and y directions. Larger field sizes result in a greater leakage at the interface plate. There is a greater leakage around the waveguide when operating in a low-energy mode, but a greater leakage for the high-energy mode at the linac face. Of the vendors investigated, the Varian 600C showed the lowest average leakage dose. The Varian 21-iX showed double the dose of the 600C. The Elekta Synergy-II had on average four times the dose leakage than the 600C, and the Siemens Primus showed an average of five times that of the 600C. All vendors show strong differences in the x and y directions. The results offer the potential for patient-positioning strategies, linac choice and shielding strategies to reduce the leakage dose to patients.

Efficacy of high-energy collimator for sentinel node lymphoscintigraphy of early breast cancer patients

IntroductionLymphoscintigraphy is an important part of sentinel node mapping in breast cancer patients. Sometimes star shaped artefacts due to septal penetration can be problematic during imaging. In the current study, we evaluated the possibility of high energy (HE) collimators use for lymphoscintigraphy.Patients and methodsTwenty patients with early breast carcinoma were included. Thirty minutes after radiotracer injection (99mTc-antimony sulphide colloid), anterior and lateral images were acquired using a dual head gamma camera equipped with a parallel hole low energy high resolution (LEHR) collimator on one head and HE collimator on another head. All images were reviewed by two nuclear medicine specialists regarding detectability and number of axillary sentinel nodes and presence of star artefact.ResultsAll images taken by LEHR collimators showed star artefact of the injection site. No image taken by HE collimator showed this effect. In two patients the sentinel node was visible only by HE collimator. Tumour location in both of these patients was in the upper lateral quadrant and both had history of excisional biopsy. In two patients additional sentinel node was visible adjacent to the first one only on the LEHR images.ConclusionsHE collimators can be used for sentinel lymph node mapping and lymphoscintigraphy of the breast cancer patients. This collimator can almost eliminate star-shaped artefacts due to septal penetration which can be advantageous in some cases. However, to separate two adjacent sentinel nodes from each other LEHR collimators perform better.

GATE based Monte Carlo simulation of planar scintigraphy to estimate the nodular dose in radioiodine therapy for autonomous thyroid adenoma

The recommended target dose in radioiodine therapy of solitary hyperfunctioning thyroid nodules is 300-400 Gy and therefore higher than in other radiotherapies. This is due to the fact that an unknown, yet significant portion of the activity is stored in extranodular areas but is neglected in the calculatory dosimetry. We investigate the feasibility of determining the ratio of nodular and extranodular activity concentrations (uptakes) from post-therapeutically acquired planar scintigrams with Monte Carlo simulations in GATE. The geometry of a gamma camera with a high energy collimator was emulated in GATE (Version 5). A geometrical thyroid-neck phantom (GP) and the ICRP reference voxel phantoms “Adult Female” (AF, 16 ml thyroid) and “Adult Male” (AM, 19 ml thyroid) were used as source regions. Nodules of 1 ml and 3 ml volume were placed in the phantoms. For each phantom and each nodule 200 scintigraphic acquisitions were simulated. Uptake ratios of nodule and rest of thyroid ranging from 1 to 20 could be created by summation. Quantitative image analysis was performed by investigating the number of simulated counts in regions of interest (ROIs). ROIs were created by perpendicular projection of the phantom onto the camera plane to avoid a user dependant bias. The ratio of count densities in ROIs over the nodule and over the contralateral lobe, which should be least affected by nodular activity, was taken to be the best available measure for the uptake ratios. However, the predefined uptake ratios are underestimated by these count density ratios: For an uptake ratio of 20 the count ratios range from 4.5 (AF, 1 ml nodule) to 15.3 (AM, 3 ml nodule). Furthermore, the contralateral ROI is more strongly affected by nodular activity than expected: For an uptake ratio of 20 between nodule and rest of thyroid up to 29% of total counts in the ROI over the contralateral lobe are caused by decays in the nodule (AF 3 ml). In the case of the 1 ml nodules this effect is smaller: 9-11% (AF) respectively 7-8% (AM). For each phantom, the dependency of count density ratios upon uptake ratios can be modeled well by both linear and quadratic regression (quadratic: r 2 > 0.99), yielding sets of parameters which in reverse allow the computation of uptake ratios (and thus dose) from count density ratios. A single regression model obtained by fitting the data of all simulations simultaneously did not provide satisfactory results except for GP, while underestimating the true uptake ratios in AF and overestimating them in AM. The scintigraphic count density ratios depend upon the uptake ratios between nodule and rest of thyroid, upon their volumes, and their respective position in a non-trivial way. Further investigations are required to derive a comprehensive rule to calculate the uptake or dose ratios based on post-therapeutic scintigraphy.

NEMA NU1-2001 performance tests of four Philips Brightview cameras

Abstract The Brightview is the latest generation dual-head SPECT and SPECT-CT camera from Philips. It is equipped with two large field of view γ-ray digital Anger detectors and with an X-ray flat panel detector. All primary and some secondary NEMA NU1-2001 performance tests were conducted on four (two SPECT and two SPECT-CT) recently installed Brightview systems mainly with 99mTc and low energy high resolution (LEHR) collimators. Intrinsic uniformity for four other isotopes (67Ga, 123I, 131I, 111In) and system uniformity with medium (ME) and high (HE) energy collimators were also measured. The measured parameters were almost identical for all the tested systems and the vast majority of measurements were within the manufacturer’s specifications. The only exception was some of the uniformity indexes of two of the heads but a new calibration solved that particular problem. System alignment could not be processed using the NEMA performance tests due to a file writing problem when performing 360° rotation for each head. However, the Philips COR test was conducted and found to be satisfactory.