Source Position Uncertainty Research Articles

Positional and angular tracking of HDR 192 Ir source for brachytherapy quality assurance using radiochromic film dosimetry.

To quantify and verify the dosimetric impact of high-dose rate (HDR) source positional uncertainty in brachytherapy, and to introduce a model for three-dimensional (3D) position tracking of the HDR source based on a two-dimensional (2D) measurement. This model has been utilized for the development of a comprehensive source quality assurance (QA) method using radiochromic film (RCF) dosimetry including assessment of different digitization uncertainties. An algorithm was developed and verified to generate 2D dose maps of the mHDR-V2 192 Ir source (Elekta, Veenendaal, Netherlands) based on the AAPM TG-43 formalism. The limits of the dosimetric error associated with source (0.9mm diameter) positional uncertainty were evaluated and experimentally verified with EBT3 film measurements for 6F (2.0mm diameter) and 4F (1.3mm diameter) size catheters at the surface (4F, 6F) and 10mm further (4F only). To quantify this uncertainty, a source tracking model was developed to incorporate the unique geometric features of all isodose lines (IDLs) within any given 2D dose map away from the source. The tracking model normalized the dose map to its maximum, then quantified the IDLs using blob analysis based on features such as area, perimeter, weighted centroid, elliptic orientation, and circularity. The Pearson correlation coefficients (PCCs) between these features and source coordinates (x, y, z, θy , θz ) were calculated. To experimentally verify the accuracy of the tracking model, EBT3 film pieces were positioned within a Solid Water® (SW) phantom above and below the source and they were exposed simultaneously. The maximum measured dosimetric variations on the 6F and 4F catheter surfaces were 39.8% and 36.1%, respectively. At 10mm further, the variation reduced to 2.6% for the 4F catheter which is in agreement with the calculations. The source center (x, y) was strongly correlated with the low IDL-weighted centroid (PCC=0.99), while the distance to source (z) was correlated with the IDL areas (PCC=0.96) and perimeters (PCC=0.99). The source orientation θy was correlated with the difference between high and low IDL-weighted centroids (PCC=0.98), while θz was correlated with the elliptic orientation of the 60-90% IDLs (PCC=0.97) for a maximum distance of z=5mm. Beyond 5mm, IDL circularity was significant, therefore limiting the determination of θz (PCC≤0.48). The measured positional errors from the film sets above and below the source indicated a source position at the bottom of the catheter (-0.24±0.07mm). Isodose line features of a 2D dose map away from the HDR source can reveal its spatial coordinates. RCF was shown to be a suitable dosimeter for source tracking and dosimetry. This technique offers a novel source QA method and has the potential to be used for QA of commercial and customized applicators.

The Bebig Valencia-type skin applicators: Dosimetric study and implementation of a dosimetric hybrid technique

PurposeTo determine the relative dose rate distribution in water for the Bebig 20 mm and 30 mm skin applicators and report results in a form suitable for potential clinical use. Results for both skin applicators are also provided in the form of a hybrid Task Group 43 (TG-43) dosimetry technique. Furthermore, the radiation leakage around both skin applicators from the radiation protection point of view and the impact of the geometrical source position uncertainties are studied and reported. Methods and MaterialsMonte Carlo simulations were performed using the MCNP 6.1 general purpose code, which was benchmarked against published dosimetry data for the Bebig Ir2.A85-2 high-dose-rate iridium-192 source, as well as the dosimetry data for the two Elekta skin applicators. Both Bebig skin applicators were modeled, and the dose rate distributions in a water phantom were calculated. The dosimetric quantities derived according to a hybrid TG-43 dosimetry technique are provided with their corresponding uncertainty values. The air kerma rate in air was simulated in the vicinity of each skin applicator to assess the radiation leakage. Results and ConclusionsResults from the Monte Carlo simulations of both skin applicators are presented in the form of figures and relative dose rate tables, and additionally with the aid of the quantities defined in the hybrid TG-43 dosimetry technique and their corresponding uncertainty values. Their output factors, flatness, and penumbra values were found comparable to the Elekta skin applicators. The radiation shielding was evaluated to be adequate. The effect of potential uncertainties in source positioning on dosimetry should be investigated as part of applicator commissioning.

First hard X-ray detection and broad-band X-ray study of the unidentified transient AX J1949.8+2534

We present the results from INTEGRAL and Swift/XRT observations of the hitherto poorly studied unidentified X-ray transient AX J1949.8+2534, and on archival multiwavelength observations of field objects. Bright hard X-ray outbursts have been discovered above 20 keV for the first time, the measured duty cycle and dynamic range are of the order of 4% and >630, respectively. The source was also detected during a low soft X-ray state (2x10E-12 erg cmE-2 sE-1) thanks to a Swift/XRT followup, which allowed for the first time to perform a soft X-ray spectral analysis as well as significantly improve the source positional uncertainty from arcminute to arcsecond size. From archival near-infrared data, we pinpointed two bright objects as most likely counterparts whose photometric properties are compatible with an early type spectral nature. This strongly supports a High Mass X-ray Binary (HMXB) scenario for AX J1949.8+2534, specifically a Supergiant Fast X-ray Transient (more likely) or alternatively a Be HMXB.

SU‐E‐T‐459: Impact of Source Position and Traveling Time On HDR Skin Surface Applicator Dosimetry

Purpose:Observed dosimetric discrepancy between measured and treatment planning system (TPS) predicted values, during applicator commissioning, were traced to source position uncertainty in the applicator. We quantify the dosimetric impact of this geometric uncertainty, and of the source traveling time inside the applicator, and propose corrections for clinical use.Methods:We measured the dose profiles from the Varian Leipzig‐style (horizontal) HDR skin applicator, using EBT3 film, photon diode, and optically stimulated luminescence dosimeter (OSLD) and three different GammaMed HDR afterloders. The dose profiles and depth dose of each aperture were measured at several depths (up to about 10 mm, depending on the dosimeter). The measured dose profiles were compared with Acuros calculated profiles in BrachyVision TPS. For the impact of the source position, EBT3 film measurements were performed with applicator, facing‐down and facing‐up orientations. The dose with and without source traveling was measured with diode detector using HDR timer and electrometer timer, respectively.Results:Depth doses measured using the three dosimeters were in good agreement, but were consistently higher than the Acuros dose calculations. Measurements with the applicator facing‐up were significantly lower than those in the facing‐down position with maximum difference of about 18% at the surface, due to source sag inside the applicator. Based on the inverse‐square law, the effective source sag was evaluated to be about 0.5 mm from the planned position. The additional dose from the source traveling was about 2.8% for 30 seconds with 10 Ci source, decreasing with increased dwelling time and decreased source activity.Conclusion:Due to the short source‐to‐surface distance of the applicator, the small source sag inside the applicator has significant dosimetric impact, which should be considered before the clinical use of the applicator. Investigation of the effect for other applicators that have relatively large source lumen inner diameter may be warranted.Christopher Barker and Gil'ad Cohen are receiving research support for a study of skin surface brachytherapy from Elekta.

Challenges for geodetic VLBI in the southern hemisphere

Inhomogeneous networks and reference frames are an important issue for Very Long Baseline Interferometry (VLBI). In this work we examine the performance of southern stations and baselines in routine VLBI experiments. A positive impact on baseline length repeatabilities of the increased observing effort by the Australian AuScope VLBI antennas is found by analysing three years of global rapid-turnaround VLBI sessions: while worse results are found for southern baselines compared to northern baselines for the first half of the investigated sessions, the northern and southern baseline length repeatabilities are about the same in the second half of the period. In simulations, the actual observing plan with a significantly lower number of observations for southern stations is identified as a major reason for the worse length WRMS for southern baselines, though other factors seem to influence the results as well. Simulating radio source position uncertainties, effects of up to 10mm are found on baseline length WRMS for long southern baselines. Improving all source position uncertainties through more frequent observations to better than 50μas could reduce this effect by up to 30%.

An interlaboratory comparison program on ELF electric and magnetic fields measurements performed in Greece: Second round of the scheme

The second round of an interlaboratory comparison program for extremely low frequency electric and magnetic fields measurements was performed at the High Voltage Laboratory of the National Technical University of Athens (Greece). The 16 participating laboratories measured the following: (i) electric field produced by a scale transmission line; (ii) magnetic field produced by a medium voltage cable; and (iii) magnetic field and frequency at the center of a standard square coil and their delivered results were evaluated in all measurement scenarios with use of performance statistics z-scores. Deviations between z-scores based on usual estimators (mean value, standard deviation) and robust estimators (derived with the robust algorithm described by the International Organization for Standardization [ISO, 2005]) highlight improved performance of the robust algorithm. An overall comparison to measurement procedure and performance results of the first round proves effectiveness and necessity of the scheme. Improper instrumentation or calibration, instability of the field source and measurement position uncertainty are factors that may cause unsatisfactory performance of the participants.

Dosimetric impact of source-positioning uncertainty in high-dose-rate balloon brachytherapy of breast cancer.

PurposeTo evaluate the dosimetric impact of source-positioning uncertainty in high-dose-rate (HDR) balloon brachytherapy of breast cancer.Material and methodsFor 49 HDR balloon patients, each dwell position of catheter(s) was manually shifted distally (+) and proximally (–) with a magnitude from 1 to 4 mm. Total 392 plans were retrospectively generated and compared to corresponding clinical plans using 7 dosimetric parameters: dose (D95) to 95% of planning target volume for evaluation (PTV_EVAL), and volume covered by 100% and 90% of the prescribed dose (PD) (V100 and V90); skin and rib maximum point dose (Dmax); normal breast tissue volume receiving 150% and 200% of PD (V150 and V200).ResultsPTV_EVAL dosimetry deteriorated with larger average/maximum reduction (from ± 1 mm to ± 4 mm) for larger source position uncertainty (p value < 0.0001): from 1.0%/2.5%, 3.3%/5.9%, 6.3%/10.0% to 9.8%/14.5% for D95; from 1.0%/2.6%, 3.1%/5.7%, 5.8%/8.9% to 8.7%/12.3% for V100; from 0.2%/1.5%, 1.0%/4.0%, 2.7%/6.8% to 5.1%/10.3% for V90. ≥ ± 3 mm shift reduced average D95 to < 95% and average V100 to < 90%. While skin and rib Dmax change was case-specific, its absolute change (∣Δ(Value)∣) showed that larger shift and high dose group had larger variation compared to smaller and lower dose group (p value < 0.0001), respectively. Normal breast tissue V150 variation was case-specific and small. Average ∣Δ(V150)∣ was 0.2 cc for the largest shift (± 4 mm) with maximum < 1.7 cc. V200 was increased with higher elevation for larger shift: from 6.4 cc/9.8 cc, 7.0 cc/10.1 cc, 8.0 cc/11.3 cc to 9.2 cc/ 13.0 cc.ConclusionsThe tolerance of ± 2 mm recommended by AAPM TG 56 is clinically acceptable in most clinical cases. However, special attention should be paid to a case where both skin and rib are located proximally to balloon, and the orientation of balloon catheter(s) is vertical to these critical structures. In this case, sufficient dosimetric planning margins are required.

On the Influence of HDR Ir-192 Source Position Uncertainty on Dose Variation within the Varian Ring Applicator

The tandem and ring (T&R) applicator is used as an alternate to tandem and ovoid (T&O) applicators to deliver HDR Ir-192 brachytherapy for cervical cancer. Since the ring interior lumen is larger than the HDR Ir-192 source capsule outer diameter, the source path within the ring is hard to predict. Some studies have shown that the actual source positions could be several millimeters different from planned positions, with potential for inducing significant dose deviation. However, other studies have demonstrated minimal dosimetric impact (Craciunescu et al 2012). Though most centers choose to implement a global source shift during commissioning (McMahon et al 2011) to limit the effect of inherent offsets, potential dose variations due to source position uncertainty are not yet well quantified. The purpose of this study was to investigate these dose variations for the worst geometry condition, and also to assess the validity of implementing a global offset using Monte Carlo (MC) simulations for dose calculation. The MCNP5 radiation transport code was used for all MC simulations. The GammaMedPlus HDR Ir-192 source core was simulated as a 0.09 cm diameter and 0.35 cm long right cylinder. Dose distributions were simulated in water (12 x 20 cm3 right cylinder) using the *F4 FMESH tally in both transverse (X-Y) and coronal (X-Z) plane. With a (0.1 cm)3 grid size, 109 photon histories gave a typical statistical error (k=1) of <1%. The Varian ring was simulated as a torus (0.29 cm and 0.35 cm inner and outer diameters) with a 0.03 cm thick titanium wall. The black buildup cap (0.5 cm) was simulated with polyoxymethylene (1.425 g/cm3) and dwell positions started from 129.5 cm with 0.5 cm step size in the ring lumen center. Dose variations for eccentric source positions were investigated by simulating dwell positions ± 0.007 cm (largest distance) from the lumen center along the Z-direction as shown in Figure 1a-c. To mimic a T&O geometry, dwell positions were simulated only in 135° to 225° and 315° to 45° as shown in Figure 1.e. To assess the influence of a global shift, ± 0.1, ± 0.3, ± 0.5 cm (Figure 1.d and 1.f), shifts were simulated distal and proximal from the ring end. Dose was normalized to 100% at 0.5 cm from the cap on the X-axis. For dose comparison, Point A was defined 2 cm up from the buildup cap and 2 cm laterally from the ring CAX on right (A_RT) and left side (A_LT). A typical dose distribution (X-Z plane) for the source in the ring lumen center was shown in Figure 1.g. Compared to sources in the ring lumen center, dose to points A_LT and A_RT changed ˗3.2% and ˗3.8%, respectively, for sources 0.007 cm away from Point A, and by 2.4% and 4.0% toward Point A, respectively. Compared to no shift, average dose to Point A was 1.6%, 2.3%, and 3.8% lower for the 0.1, 0.3, and 0.5 cm distal global source shifts, respectively. Doses were 1.2%, 1.4%, and 2.6% lower for the proximal shifts. Neither source position uncertainty within ring lumen nor global source shift caused significant dose variation to either point A_RT or point A_LT. Dose variation due to source position uncertainty was small (< 4%), and can be attributed mostly to inverse square law. Dose variations due to global source shifts also were not substantial. Applying a global shift will improve the accuracy of the dose distribution, but not applying the shift or applying a shift in wrong direction may not cause substantial dose calculation errors.

Influence of imaging source and panel position uncertainties on the accuracy of 2D/3D image registration of cranial images

To determine the effects of imager source and panel positioning uncertainties on the accuracy of dual intensity-based 2D∕3D image registration of cranial images. An open source 2D∕3D image registration algorithm has been developed for registration of two orthogonal x-rays to a 3D volumetric image. The initialization files of the algorithm allow for nine degrees of freedom system calibration including x, y, z positions of the source and panel, and three rotational degrees of freedom of the panel about each of the three translational axes. A baseline system calibration was established and a baseline 2D∕3D registration between two orthogonal x-rays and the volumetric image was determined. The calibration file was manipulated to insert errors into each of the nine calibration variables of both imager geometries. Rigid six degrees of freedom registrations were iterated for each panel or source positional error over a range of predetermined calibration errors to determine the resulting error in the registration versus the baseline registration due to the manipulated error of the panel or source calibration. Panel and source translational errors orthogonal to the imager∕panel axis introduced the greatest errors in the registration accuracy (4.0 mm geometric error results in up to 2.7 mm registration error). Panel rotation about the imaging direction also resulted in errors of the registration (2.0° geometric error results in up to 1.7° registration error). Differences in magnification and panel tilt and roll, i.e., source and∕or panel translation along the imaging direction and panel rotations about the orthogonal axes had minimal effects on the registration accuracy (below 0.3 mm and 0.2° registration error). While five of the nine imaging system variables were found to have a considerable effect on 2D∕3D registration accuracy of cranial images, the other four variables showed minimal effects. Vendors typically provide simplified calibration procedures which aim to remove encountered geometric uncertainties by accounting for two panel translations. This study shows that at least the five relevant positional variables should be separately calibrated, if accurate alignment is required for 2D∕3D registration.

Identifying afterloading PDR and HDR brachytherapy errors using real-time fiber-coupled Al2O3:C dosimetry and a novel statistical error decision criterion

Background and purposeThe feasibility of a real-time in vivo dosimeter to detect errors has previously been demonstrated. The purpose of this study was to: (1) quantify the sensitivity of the dosimeter to detect imposed treatment errors under well controlled and clinically relevant experimental conditions, and (2) test a new statistical error decision concept based on full uncertainty analysis. Materials and methodsPhantom studies of two gynecological cancer PDR and one prostate cancer HDR patient treatment plans were performed using tandem ring applicators or interstitial needles. Imposed treatment errors, including interchanged pairs of afterloader guide tubes and 2–20mm source displacements, were monitored using a real-time fiber-coupled carbon doped aluminum oxide (Al2O3:C) crystal dosimeter that was positioned in the reconstructed tumor region. The error detection capacity was evaluated at three dose levels: dwell position, source channel, and fraction. The error criterion incorporated the correlated source position uncertainties and other sources of uncertainty, and it was applied both for the specific phantom patient plans and for a general case (source-detector distance 5–90mm and position uncertainty 1–4mm). ResultsOut of 20 interchanged guide tube errors, time-resolved analysis identified 17 while fraction level analysis identified two. Channel and fraction level comparisons could leave 10mm dosimeter displacement errors unidentified. Dwell position dose rate comparisons correctly identified displacements ⩾5mm. ConclusionThis phantom study demonstrates that Al2O3:C real-time dosimetry can identify applicator displacements ⩾5mm and interchanged guide tube errors during PDR and HDR brachytherapy. The study demonstrates the shortcoming of a constant error criterion and the advantage of a statistical error criterion.

Three-dimensional source tracking in an uncertain environment via Bayesian marginalization

This paper develops a non-linear Bayesian marginalization approach for three-dimensional source tracking in shallow water with uncertain environmental properties. The algorithm integrates the posterior probability density via a combination of Metropolis-Hastings sampling over environmental and bearing model parameters and Gibbs sampling over source range/depth, with track constraints on source velocity applied. Marginal distributions for source range/depth and source bearing are derived, with source position uncertainties estimated from the distributions. The Viterbi algorithm is applied to obtain the most probable three-dimensional track. The approach is applied to experimental narrowband data recorded on a bottom-moored horizontal line array in the Barents Sea.

Investigation of source position uncertainties &amp; balloon deformation in MammoSite brachytherapy on treatment effectiveness

The MammoSite breast high dose rate brachytherapy is used in treatment of early-stage breast cancer. The tumour bed volume is irradiated with high dose per fraction in a relatively small number of fractions. Uncertainties in the source positioning and MammoSite balloon deformation will alter the prescribed dose within the treated volume. They may also expose the normal tissues in balloon proximity to excessive dose. The purpose of this work is to explore the impact of these two uncertainties on the MammoSite dose distribution in the breast using dose volume histograms and Monte Carlo simulations. The Lyman-Kutcher and relative seriality models were employed to estimate the normal tissues complications associated with the MammoSite dose distributions. The tumour control probability was calculated using the Poisson model. This study gives low probabilities for developing heart and lung complications. The probability of complications of the skin and normal breast tissues depends on the location of the source inside the balloon and the volume receiving high dose. Incorrect source position and balloon deformation had significant effect on the prescribed dose within the treated volume. A 4 mm balloon deformation resulted in reduction of the tumour control probability by 24%. Monte Carlo calculations using EGSnrc showed that a deviation of the source by 1 mm caused approximately 7% dose reduction in the treated target volume at 1 cm from the balloon surface. In conclusion, accurate positioning of the (192)Ir source at the balloon centre and minimal balloon deformation are critical for proper dose delivery with the MammoSite brachytherapy applicator. On the basis of this study, we suggest that the MammoSite treatment protocols should allow for a balloon deformation of < or = 2 mm and a maximum source deviation of < or = 1 mm.

TH‐C‐AUD A‐01: A Systematic Analysis of Errors and Uncertainties in Partial Breast Irradiation Using the MammoSite Balloon Catheter

Purpose: The objective of this study was to evaluate systematic and random errors associated with HDR brachytherapy treatment delivery of partial breast irradiation with a MammoSite Balloon. The impact of these errors on the actual delivered dose was studied. Method and Materials: The effect of respiratory motion, balloon contrast concentration and intra‐observer variability on accuracy of applicator delineation were investigated. Additionally, the consequence of variability of target delineation and dose matrix voxel size was considered in relationship to target coverage. Lastly, an analysis of 15 patients treated with the MammoSite was performed to simulate the effect of allowed source position uncertainty for each fraction. Results: Respiratory motion resulted in an under‐estimation of the balloon volume of 8% and 18% for computed tomography and cone‐beam computed tomography, respectively. The coverage was assessed based on the volume of the target receiving 95% of the prescribed dose (V95). On average, balloon volume underestimation combined with the daily ±1.0mm source position uncertainty degraded the coverage from an initial 96.3% to 91.7% over the course of 10 fractions. Additionally, a 3mm difference between the true tip of the applicator and its delineated position resulted in a decrease in coverage from 96.3% to 92.6% and from 98.7% to 79.3%, for a small and a large balloon, respectively. Conclusion: Current treatment protocols require that 90% of the target volume receives 90% of the prescription dose. Our findings suggest that significantly higher dosimetric coverage goals are necessary to compensate for the identified errors inherent in balloon based brachytherapy dose delivery. This will insure that the expected degradation of the actual dose delivered from the planned dose, as a consequence of random and systematic uncertainties, does not fall below an acceptable threshold.

AzTEC millimetre survey of the COSMOS field – I. Data reduction and source catalogue

We present a 1.1mm wavelength imaging survey covering 0.3 deg^2 in the COSMOS field. These data, obtained with the AzTEC continuum camera on the James Clerk Maxwell Telescope, were centred on a prominent large-scale structure overdensity which includes a rich X-ray cluster at z ≈ 0.73. A total of 50 mm-galaxy candidates, with a significance ranging from 3.5 to 8.5σ, are extracted from the central 0.15 deg^2 area which has a uniform sensitivity of ∼1.3 mJy beam^−1. 16 sources are detected with S/N ≥ 4.5, where the expected false detection rate is zero, of which a surprisingly large number (9) have intrinsic (deboosted) fluxes ≥5 mJy at 1.1 mm. Assuming the emission is dominated by radiation from dust, heated by a massive population of young, optically obscured stars, then these bright AzTEC sources have far-infrared luminosities >6 × 10^(12)L_☉ and star formation rates ≥1100M_☉ yr^(−1). Two of these nine bright AzTEC sources are found towards the extreme peripheral region of the X-ray cluster, whilst the remainder are distributed across the larger scale overdensity. We describe the AzTEC data reduction pipeline, the source-extraction algorithm, and the characterization of the source catalogue, including the completeness, flux deboosting correction, false-detection rate and the source positional uncertainty, through an extensive set of Monte Carlo simulations. We conclude with a preliminary comparison, via a stacked analysis, of the overlapping MIPS 24-μm data and radio data with this AzTEC map of the COSMOS field.

Probing the nature of IGR J16493−4348: spectral and temporal analysis of the 1-100 keV emission

IGR J16493?4348 was one of the first new sources to be detected by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) ?-ray telescope in the 18-100 keV energy band. Based on spatial coincidence, the source was originally associated with the free radio pulsar PSR J1649?4349. Presented here are the results of 2.8 Ms of observations made by the INTEGRAL mission and a 5.6-ks observation with the Swift/X-ray Telescope (XRT). Spectral analysis indicates that the source is best modelled by an absorbed power law with a high energy cut-off at Ecut? 15 keV and a hydrogen absorbing column of NH= 5.4+1.3?1× 1022?cm?2 . Analysis of the light curves indicates that the source is a weak, persistent ?-ray emitter showing indications of variability in the 2-9 and 22-100 keV bands. The average source flux is ?1.1 × 10?10?erg?cm?2?s?1 in the 1-100 keV energy band. No coherent timing signal is identified at any time-scale in the INTEGRAL or Swift data. The refined source location and positional uncertainty of IGR J16493?4348 places PSR J1649?4349 outside the 90 per cent error circle. We conclude that IGR J16493?4348 is not associated with PSR J1649?4349. Combining the INTEGRAL observations with Swift/XRT data and information gathered by RXTE and Chandra, we suggest that IGR J16493?4348 is an X-ray binary, and that the source characteristics favour a high-mass X-ray binary although a low-mass X-ray binary nature cannot be ruled out.

INTEGRAL/XMM views on the MeV source GRO J1411-64

The COMPTEL unidentified source GRO J 1411-64 was observed by INTEGRAL and XMM-Newton in 2005. The Circinus Galaxy is the only source detected within the 4$\sigma$ location error of GRO J1411-64, but in here excluded as the possible counterpart. At soft X-rays, 22 reliable and statistically significant sources (likelihood $> 10$) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6 -635932, is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the COMPTEL source position uncertainty make an association hard to quantify and thus risky. At the best location of the source, detections at hard X-rays show only upper limits, which, together with MeV results obtained by COMPTEL suggest the existence of a peak in power output located somewhere between 300-700 keV for the so-called low state. Such a spectrum resembles those in blazars or microquasars, and might suggest at work by a similar scenario. However, an analysis using a microquasar model consisting on a magnetized conical jet filled with relativistic electrons, shows that it is hard to comply with all observational constrains. This fact and the non-detection at hard X-rays introduce an a-posteriori question mark upon the physical reality of this source, what is discussed here.

Chandra Multiwavelength Project X‐Ray Point Source Catalog

We present the Chandra Multiwavelength Project (ChaMP) X-ray point source catalog with ~6800 X-ray sources detected in 149 Chandra observations covering ~10 deg2. The full ChaMP catalog sample is 7 times larger than the initial published ChaMP catalog. The exposure time of the fields in our sample ranges from 0.9 to 124 ks, corresponding to a deepest X-ray flux limit of f0.5-8.0 = 9 × 10-16 ergs cm-2 s-1. The ChaMP X-ray data have been uniformly reduced and analyzed with ChaMP-specific pipelines and then carefully validated by visual inspection. The ChaMP catalog includes X-ray photometric data in eight different energy bands as well as X-ray spectral hardness ratios and colors. To best utilize the ChaMP catalog, we also present the source reliability, detection probability, and positional uncertainty. To quantitatively assess those parameters, we performed extensive simulations. In particular, we present a set of empirical equations: the flux limit as a function of effective exposure time and the positional uncertainty as a function of source counts and off-axis angle. The false source detection rate is ~1% of all detected ChaMP sources, while the detection probability is better than ~95% for sources with counts 30 and off-axis angle <5'. The typical positional offset between ChaMP X-ray source and their SDSS optical counterparts is 0.7'' ± 0.4'', derived from ~900 matched sources.

INTEGRAL and XMM-Newton observations towards the unidentified MeV source GRO J1411-64

Aims. We investigate the nature of the COMPTEL unidentified source GRO J1411-64. Methods. The source was observed by INTEGRAL. Its central part was also observed by XMM-Newton. Results. The data analysis shows no hint for new detections at hard X-rays. The upper limits in flux herein presented constrain the energy spectrum of whatever was producing GRO J1411-64, imposing, in the framework of earlier COMPTEL observations, the existence of a peak in power output located somewhere between 300-700 keV for the so-called low state. The Circinus Galaxy is the only source detected within the 4 sigma location error of GRO J1411-64, but can be safely excluded as the possible counterpart: the extrapolation of the energy spectrum is well below the one for GRO J1411-64 at MeV energies. 22 reliable and statistically significant sources (likelihood > 10) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6-635932, is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the COMPTEL source position uncertainty make an association hard to quantify and thus risky. Conclusions. The unique peak of the power output at high energies (hard X-rays and gamma-rays) resembles that found in the SED seen in blazars or microquasars, and might suggest that a similar scenario is at work. However, an analysis using a microquasar model consisting on a magnetized conical jet filled with relativistic electrons which radiate through synchrotron and inverse Compton scattering with star, disk, corona and synchrotron photons shows that it is hard to comply with all observational constrains. This fact and the non-detection at hard X-rays introduce an a-posteriori question mark upon the physical reality of this source, which is discussed in some detail.

Bayesian Sonar Detection Performance Prediction With Source Position Uncertainty Using SWellEx-96 Vertical Array Data

Predicting sonar detection performance is important for the development of sonar systems. The classical sonar equation cannot accurately predict sonar detection performance because it does not incorporate the effect of ocean environmental and source position uncertainty. We propose an analytical receiver operating characteristic (ROC) expression that characterizes the performance of the optimal Bayesian detector in the presence of ocean environmental and source position uncertainty. The approach is based on a statistical model of the environment and a physical model of acoustic propagation, which translates ocean environmental and source position uncertainty to signal wavefront uncertainty. The analytical ROC expression developed in this paper is verified for source position uncertainty due to source motion using both simulated data and real data collected during the Shallow Water Evaluation Cell Experiment (SWellEx-96). The results showed that the primary effect of source position uncertainty on optimal sonar detection performance is captured by the rank that corresponds to the significant eigenvalues of the signal matrix, an ensemble of replica signal wavefronts (normalized acoustic pressure vector) at the receiving array. The results also showed that the proposed ROC expression provides a realistic detection performance prediction for the Bayesian detector for source position uncertainty using real data. The proposed approach to sonar detection performance prediction is much simpler and faster than those using conventional Monte Carlo approaches

Evaluation of a TG-43 compliant analytical dosimetry model in clinical 192Ir HDR brachytherapy treatment planning and assessment of the significance of source position and catheter reconstruction uncertainties

A simple, time efficient, analytical model incorporating heterogeneities and body dimensions around a point 192Ir source is generalized for accurate dosimetry around commercially available 192Ir brachytherapy sources. The generalized model was verified in dosimetry of a clinical 192Ir high dose rate prostate monotherapy application, involving 16 catheters and 83 source dwell positions, through comparison with corresponding treatment planning system data. The computational time efficiency and accuracy of the proposed model allowed the assessment of the impact that uncertainties in source dwell positions and catheter reconstruction may have on dose distributions, and how these could potentially affect the clinical outcome. Results revealed that a 0.1 cm catheter reconstruction uncertainty and a 0.15 cm source position uncertainty along the catheter lead to a dose uncertainty of less than 2% for doses lower than 200% of the prescribed dose, reaching up to 5% for points lying in close proximity to the catheters. These uncertainties were found to have no impact (less than 1%) on dose volume histogram results of both the planning target volume and the urethra. A catheter reconstruction uncertainty as high as 0.2 cm results in a dose uncertainty greater than 2%, reaching up to 9%, only for points inside the 150% contour. However, even in this case, the impact on dose volume histogram calculations is less than 3%.