bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of the effects of treatment planning variables in small animal radiotherapy dose distributions
Authors: Motomura Amy R. , Bazalova Magdalena , Zhou Hu , Keall Paul J. , Graves Edward E. 
Published: January 2010

Purpose:Methods used for small animal radiation treatment have yet to achieve the same dose targeting as in clinical radiation therapy. Toward understanding how to better plan small animal radiation using a system recently developed for this purpose, the authors characterized dose distributions produced from conformal radiotherapy of small animals in a microCT scanner equipped with a variable‐aperture collimator.Methods:Dose distributions delivered to a cylindrical solid water phantom were simulated using a Monte Carlo algorithm. Phase‐space files for 120 kVp x‐ray beams and collimator widths of 1–10 mm at isocenter were generated using BEAMnrc software, and dose distributions for evenly spaced beams numbered from 5 to 80 were generated in DOSXYZnrc for a variety of targets, including centered spherical targets in a range of sizes, spherical targets offset from centered by various distances, and various ellipsoidal targets. Dose distributions were analyzed using dose volume histograms. The dose delivered to a mouse bearing a spontaneous lung tumor was also simulated, and dose volume histograms were generated for the tumor, heart, left lung, right lung, and spinal cord.Results:Results indicated that for centered, symmetric targets, the number of beams required to achieve a smooth dose volume histogram decreased with increased target size. Dose distributions for noncentered, symmetric targets did not exhibit any significant loss of conformality with increasing offset from the phantom center, indicating sufficient beam penetration through the phantom for targeting superficial targets from all angles. Even with variable collimator widths, targeting of asymmetric targets was found to have less conformality than that of spherical targets. Irradiation of a mouse lung tumor with multiple beam widths was found to effectively deliver dose to the tumor volume while minimizing dose to other critical structures.Conclusions:Overall, this method of generating and analyzing dose distributions provides a quantitative method for developing practical guidelines for small animal radiotherapy treatment planning. Future work should address methods to improve conformality in asymmetric targets.
A new metric for assessing IMRT modulation complexity and plan deliverability
Authors: McNiven Andrea L. , Sharpe Michael B. , Purdie Thomas G. 
Published: January 2010

Purpose:To evaluate the utility of a new complexity metric, the modulation complexity score (MCS), in the treatment planning and quality assurance processes and to evaluate the relationship of the metric with deliverability.Methods:A multisite (breast, rectum, prostate, prostate bed, lung, and head and neck) and site‐specific (lung) dosimetric evaluation has been completed. The MCS was calculated for each beam and the overall treatment plan. A 2D diode array (MapCHECK™, Sun Nuclear, Melbourne, FL) was used to acquire measurements for each beam. The measured and planned dose (PINNACLE3, Phillips, Madison, WI) was evaluated using different percent differences and distance to agreement (DTA) criteria (3%/3 mm and 2%/1 mm) and the relationship between the dosimetric results and complexity (as measured by the MCS or simple beam parameters) assessed.Results:For the multisite analysis (243 plans total), the mean MCS scores for each treatment site were breast (0.92), rectum (0.858), prostate (0.837), prostate bed (0.652), lung (0.631), and head and neck (0.356). The MCS allowed for compilation of treatment site‐specific statistics, which is useful for comparing different techniques, as well as for comparison of individual treatment plans with the typical complexity levels. For the six plans selected for dosimetry, the average diode percent pass rate was 98.7% (minimum of 96%) for 3%/3 mm evaluation criteria. The average difference in absolute dose measurement between the planned and measured dose was 1.7 cGy. The detailed lung analysis also showed excellent agreement between the measured and planned dose, as all beams had a diode percentage pass rate for 3%/3 mm criteria of greater than 95.9%, with an average pass rate of 99.0%. The average absolute maximum dose difference for the lung plans was 0.7 cGy. There was no direct correlation between the MCS and simple beam parameters which could be used as a surrogate for complexity level (i.e., number of segments or MU). An evaluation criterion of 2%/1 mm reliably allowed for the identification of beams that are dosimetrically robust. In this study we defined a robust beam or plan as one that maintained a diode percentage pass rate greater than 90% at 2%/1 mm, indicating delivery that was deemed accurate when compared to the planned dose, even under stricter evaluation criterion. MCS and MU threshold criteria were determined by defining a required specificity of 1.0. A MCS threshold of 0.8 allowed for identification of robust deliverability with a sensitivity of 0.36. In contrast, MU had a lower sensitivity of 0.23 for a threshold of 50 MU.Conclusions:The MCS allows for a quantitative assessment of plan complexity, on a fixed scale, that can be applied to all treatment sites and can provide more information related to dose delivery than simple beam parameters. This could prove useful throughout the entire treatment planning and QA process.
Development and validation of segmentation and interpolation techniques in sinograms for metal artifact suppression in CT
Authors: Veldkamp Wouter J. H. , Joemai Raoul M. S. , van der Molen Aart J. , Geleijns Jacob 
Published: January 2010

Purpose:Metal prostheses cause artifacts in computed tomography (CT) images. The purpose of this work was to design an efficient and accurate metal segmentation in raw data to achieve artifact suppression and to improve CT image quality for patients with metal hip or shoulder prostheses.Methods:The artifact suppression technique incorporates two steps: metal object segmentation in raw data and replacement of the segmented region by new values using an interpolation scheme, followed by addition of the scaled metal signal intensity. Segmentation of metal is performed directly in sinograms, making it efficient and different from current methods that perform segmentation in reconstructed images in combination with Radon transformations. Metal signal segmentation is achieved by using a Markov random field model (MRF). Three interpolation methods are applied and investigated. To provide a proof of concept, CT data of five patients with metal implants were included in the study, as well as CT data of a PMMA phantom with Teflon, PVC, and titanium inserts. Accuracy was determined quantitatively by comparing mean Hounsfield (HU) values and standard deviation (SD) as a measure of distortion in phantom images with titanium (original and suppressed) and without titanium insert. Qualitative improvement was assessed by comparing uncorrected clinical images with artifact suppressed images.Results:Artifacts in CT data of a phantom and five patients were automatically suppressed. The general visibility of structures clearly improved. In phantom images, the technique showed reduced SD close to the SD for the case where titanium was not inserted, indicating improved image quality. HU values in corrected images were different from expected values for all interpolation methods. Subtle differences between interpolation methods were found.Conclusions:The new artifact suppression design is efficient, for instance, in terms of preserving spatial resolution, as it is applied directly to original raw data. It successfully reduced artifacts in CT images of five patients and in phantom images. Sophisticated interpolation methods are needed to obtain reliable HU values close to the prosthesis.
The design of a simulated in‐line side‐coupled 6 MV linear accelerator waveguide
Authors: St. Aubin Joel , Steciw Stephen , Fallone B. G. 
Published: January 2010

Purpose:The design of a 3D in‐line side‐coupled 6 MV linac waveguide for medical use is given, and the effect of the side‐coupling and port irises on the radio frequency (RF), beam dynamics, and dosimetric solutions is examined. This work was motivated by our research on a linac‐MR hybrid system, where accurate electron trajectory information for a clinical medical waveguide in the presence of an external magnetic field was needed.Methods:For this work, the design of the linac waveguide was generated using the finite element method. The design outlined here incorporates the necessary geometric changes needed to incorporate a full‐end accelerating cavity with a single‐coupling iris, a waveguide‐cavity coupling port iris that allows power transfer into the waveguide from the magnetron, as well as a method to control the RF field magnitude within the first half accelerating cavity into which the electrons from the gun are injected.Results:With the full waveguide designed to resonate at, a full 3D RF field solution was obtained. The accuracy of the 3D RF field solution was estimated through a comparison of important linac parameters ( factor, shunt impedance, transit time factor, and resonant frequency) calculated for one accelerating cavity with the benchmarked program SUPERFISH. It was found that the maximum difference between the 3D solution and SUPERFISH was less than 0.03%. The eigenvalue solver, which determines the resonant frequencies of the 3D side‐coupled waveguide simulation, was shown to be highly accurate through a comparison with lumped circuit theory. Two different waveguide geometries were examined, one incorporating a 0.5 mm first side cavity shift and another with a 1.5 mm first side cavity shift. The asymmetrically placed side‐coupling irises and the port iris for both models were shown to introduce asymmetries in the RF field large enough to cause a peak shift and skewing (center of gravity minus peak shift) of an initially cylindrically uniform electron beam accelerating within the waveguide. The shifting and skewing of the electron beam were found to be greatest due to the effects of the side‐coupling irises on the RF field. A further Monte Carlo study showed that this effect translated into a 1% asymmetry in a field dose profile.Conclusions:A full 3D design for an in‐line side‐coupled 6 MV linear accelerator that emulates a common commercial waveguide has been given. The effect of the side coupling on the dose distribution has been shown to create a slight asymmetry, but overall does not affect the clinical applicability of the linac. The 3D in‐line side‐coupled linac model further provides a tool for the investigation of linac performance within an external magnetic field, which exists in an integrated linac‐MR system.
Development of a population‐based model of surface segmentation uncertainties for uncertainty‐weighted deformable image registrations
Authors: Wu Jian , Murphy Martin J. , Weiss Elisabeth , Sleeman William C. , Williamson Jeffrey 
Published: January 2010

Purpose:To develop a population‐based model of surface segmentation uncertainties for uncertainty‐weighted surface‐based deformable registrations.Methods:The contours of the prostate, the bladder, and the rectum were manually delineated by five observers on fan beam CT images of four prostate cancer patients. First, patient‐specific representations of structure segmentation uncertainties were derived by determining the interobserver variability (i.e., standard deviation) of the structure boundary delineation. This was achieved by (1) generating an average structure surface mesh from the structure contours drawn by different observers, and (2) calculating three‐dimensional standard deviation surface meshes (SDSMs) based on the perpendicular distances from the individual boundary surface meshes to the average surface mesh computed above. Then an average structure surface mesh was constructed to be the reference mesh for the population‐based model. The average structure meshes of the other patients were deformably registered to the reference mesh. The calculated deformable vector fields were used to map the patient‐specific SDSMs to the reference mesh to obtain the registered SDSMs. Finally, the population‐based SDSM was derived by taking the average of the registered SDSMs in quadrature.Results:Population‐based structure surface statistical models of the prostate, the bladder, and the rectum were created by mapping the patient‐specific SDSMs to the population surface model. Graphical visualization indicates that the boundary uncertainties are dependent on anatomical location.Conclusions:The authors have developed and demonstrated a general method for objectively constructing surface maps of uncertainties derived from topologically complex structure boundary segmentations from multiple observers. The computed boundary uncertainties have significant spatial variations. They can be used as weighting factors for surface‐based probabilistic deformable registration.
Quantifying the effect of anode surface roughness on diagnostic x‐ray spectra using Monte Carlo simulation
Authors: Mehranian A. , Ay M. R. , Alam N. Riyahi , Zaidi H. 
Published: January 2010

Purpose:The accurate prediction of x‐ray spectra under typical conditions encountered in clinical x‐ray examination procedures and the assessment of factors influencing them has been a long‐standing goal of the diagnostic radiology and medical physics communities. In this work, the influence of anode surface roughness on diagnostic x‐ray spectra is evaluated using MCNP4C‐based Monte Carlo simulations.Methods:An image‐based modeling method was used to create realistic models from surface‐cracked anodes. An in‐house computer program was written to model the geometric pattern of cracks and irregularities from digital images of focal track surface in order to define the modeled anodes into MCNP input file. To consider average roughness and mean crack depth into the models, the surface of anodes was characterized by scanning electron microscopy and surface profilometry. It was found that the average roughness in the most aged tube studied is about . The correctness of MCNP4C in simulating diagnostic x‐ray spectra was thoroughly verified by calling its Gaussian energy broadening card and comparing the simulated spectra with experimentally measured ones. The assessment of anode roughness involved the comparison of simulated spectra in deteriorated anodes with those simulated in perfectly plain anodes considered as reference. From these comparisons, the variations in output intensity, half value layer (HVL), heel effect, and patient dose were studied.Results:An intensity loss of 4.5% and 16.8% was predicted for anodes aged by 5 and deep cracks (50 kVp, 6° target angle, and 2.5 mm Al total filtration). The variations in HVL were not significant as the spectra were not hardened by more than 2.5%; however, the trend for this variation was to increase with roughness. By deploying several point detector tallies along the anode‐cathode direction and averaging exposure over them, it was found that for a 6° anode, roughened by deep cracks, the reduction in exposure is 14.9% and 13.1% for 70 and 120 kVp tube voltages, respectively. For the evaluation of patient dose, entrance skin radiation dose was calculated for typical chest x‐ray examinations. It was shown that as anode roughness increases, patient entrance skin dose decreases averagely by a factor of 15%.Conclusions:It was concluded that the anode surface roughness can have a non‐negligible effect on output spectra in aged x‐ray imaging tubes and its impact should be carefully considered in diagnostic x‐ray imaging modalities.
Automated segmentation and quantification of liver and spleen from CT images using normalized probabilistic atlases and enhancement estimation
Authors: Linguraru Marius George , Sandberg Jesse K. , Li Zhixi , Shah Furhawn , Summers Ronald M. 
Published: January 2010

Purpose:To investigate the potential of the normalized probabilistic atlases and computer‐aided medical image analysis to automatically segment and quantify livers and spleens for extracting imaging biomarkers (volume and height).Methods:A clinical tool was developed to segment livers and spleen from 257 abdominal contrast‐enhanced CT studies. There were 51 normal livers, 44 normal spleens, 128 splenomegaly, 59 hepatomegaly, and 23 partial hepatectomy cases. 20 more contrast‐enhanced CT scans from a public site with manual segmentations of mainly pathological livers were used to test the method. Data were acquired on a variety of scanners from different manufacturers and at varying resolution. Probabilistic atlases of livers and spleens were created using manually segmented data from ten noncontrast CT scans (five male and five female). The organ locations were modeled in the physical space and normalized to the position of an anatomical landmark, the xiphoid. The construction and exploitation of liver and spleen atlases enabled the automated quantifications of liver/spleen volumes and heights (midhepatic liver height and cephalocaudal spleen height) from abdominal CT data. The quantification was improved incrementally by a geodesic active contour, patient specific contrast‐enhancement characteristics passed to an adaptive convolution, and correction for shape and location errors.Results:The livers and spleens were robustly segmented from normal and pathological cases. For the liver, the Dice/Tanimoto volume overlaps were 96.2%/92.7%, the volume/height errors were 2.2%/2.8%, the root‐mean‐squared error (RMSE) was 2.3 mm, and the average surface distance (ASD) was 1.2 mm. The spleen quantification led to 95.2%/91% Dice/Tanimoto overlaps, 3.3%/1.7% volume/height errors, 1.1 mm RMSE, and 0.7 ASD. The correlations with clinical/manual height measurements were 0.97 and 0.93 for the spleen and liver, respectively . No significant difference was found comparing interobserver and automatic‐manual volume/height errors for liver and spleen.Conclusions:The algorithm is robust to segmenting normal and enlarged spleens and livers, and in the presence of tumors and large morphological changes due to partial hepatectomy. Imaging biomarkers of the liver and spleen from automated computer‐assisted tools have the potential to assist the diagnosis of abdominal disorders from routine analysis of clinical data and guide clinical management.
Comparison of different computed radiography systems: Physical characterization and contrast detail analysis
Authors: Rivetti Stefano , Lanconelli Nico , Bertolini Marco , Nitrosi Andrea , Burani Aldo , Acchiappati Domenico 
Published: January 2010

Purpose:In this study, five different units based on three different technologies—traditional computed radiography (CR) units with granular phosphor and single‐side reading, granular phosphor and dual‐side reading, and columnar phosphor and line‐scanning reading—are compared in terms of physical characterization and contrast detail analysis.Methods:The physical characterization of the five systems was obtained with the standard beam condition RQA5. Three of the units have been developed by FUJIFILM (FCR ST‐VI, FCR ST‐BD, and FCR Velocity U), one by Kodak (Direct View CR 975), and one by Agfa (DX‐S). The quantitative comparison is based on the calculation of the modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). Noise investigation was also achieved by using a relative standard deviation analysis. Psychophysical characterization is assessed by performing a contrast detail analysis with an automatic reading of CDRAD images.Results:The most advanced units based on columnar phosphors provide MTF values in line or better than those from conventional CR systems. The greater thickness of the columnar phosphor improves the efficiency, allowing for enhanced noise properties. In fact, NPS values for standard CR systems are remarkably higher for all the investigated exposures and especially for frequencies up to 3.5 lp/mm. As a consequence, DQE values for the three units based on columnar phosphors and line‐scanning reading, or granular phosphor and dual‐side reading, are neatly better than those from conventional CR systems. Actually, DQE values of about 40% are easily achievable for all the investigated exposures.Conclusions:This study suggests that systems based on the dual‐side reading or line‐scanning reading with columnar phosphors provide a remarkable improvement when compared to conventional CR units and yield results in line with those obtained from most digital detectors for radiography.
Filtered region of interest cone‐beam rotational angiography
Authors: Schafer Sebastian , Noël Peter B. , Walczak Alan M. , Hoffmann Kenneth R. 
Published: January 2010

Purpose:Cone‐beam rotational angiography (CBRA) is widely used in the modern clinical settings. In a number of procedures, the area of interest is often considerably smaller than the field of view (FOV) of the detector, subjecting the patient to potentially unnecessary x‐ray dose. The authors therefore propose a filter‐based method to reduce the dose in the regions of low interest, while supplying high image quality in the region of interest (ROI).Methods:For such procedures, the authors propose a method of filtered region of interest (FROI)‐CBRA. In the authors’ approach, a gadolinium filter with a circular central opening is placed into the x‐ray beam during image acquisition. The central region is imaged with high contrast, while peripheral regions are subjected to a substantial lower intensity and dose through beam filtering. The resulting images contain a high contrast/intensity ROI, as well as a low contrast/intensity peripheral region, and a transition region in between. To equalize the two regions’ intensities, the first projection of the acquisition is performed with and without the filter in place. The equalization relationship, based on Beer's law, is established through linear regression using corresponding filtered and nonfiltered data. The transition region is equalized based on radial profiles.Results:Evaluations in 2D and 3D show no visible difference between conventional FROI‐CBRA projection images and reconstructions in the ROI. CNR evaluations show similar image quality in the ROI, with a reduced CNR in the reconstructed peripheral region. In all filtered projection images, the scatter fraction inside the ROI was reduced. Theoretical and experimental dose evaluations show a considerable dose reduction; using a ROI half the original FOV reduces the dose by 60% for the filter thickness of 1.29 mm.Conclusions:These results indicate the potential of FROI‐CBRA to reduce the dose to the patient while supplying the physician with the desired image detail inside the ROI.