bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact of JPEG 2000 compression on lesion detection in MR imaging
Authors: Paz Juan , Pérez Marlen , Schelkens Peter , Rodríguez José 
Published: October 2009

Purpose:Lossy compression algorithms enable the efficient transmission of large medical image datasets over bandwidth‐limited digital networks or facilitate the long‐term storage of the daily image production. Although JPEG 2000 has been adopted by DICOM as the standard for lossy‐to‐lossless compression, still a set of guidelines needs to be derived that allows for the usage of the lossy mode, potentially jeopardizing the accuracy of lesion detection and characterization, and so, of the resulting diagnosis task effectiveness in the medical diagnosis process. In this article the authors present and evaluate a generic methodology for the determination of the minimal bit rate that still ensures an accurate detection in magnetic resonance images of specific lesions. In this article, they demonstrate the methodology for two particular pathologies, i.e., multiple sclerosis and Virchow–Robin space enlargements.Methods:Involving qualified personnel, the minimal bit rate is estimated from ROC experiments initially simulated through mathematical observers that are designed with several objective metrics. The mathematical observer models included three variants of the Hotelling observer plus the nonprewhitening matched filter with eye model, while the objective measures are based on distance, correlation, singular value decomposition, and structural similarity.Results:The results indicate that the highest compression without seriously affecting the detection of the studied lesions is achieved at a bit rate of 0.125 bpp. At this value, the detection effectiveness exceeded 95% with less than 5% standard deviation, while only 4.4% of the outcomes were classified as false negatives by the experts and 11.6% as false positives.Conclusions:The optimal bit rate found assures that important information on the small investigated structures is still preserved for their accurate detection and their a posteriori characterization.
Time‐resolved in vivo luminescence dosimetry for online error detection in pulsed dose‐rate brachytherapy
Authors: Andersen Claus E. , Nielsen Søren Kynde , Lindegaard Jacob Christian , Tanderup Kari 
Published: October 2009

Purpose:The purpose of this study is to present and evaluate a dose‐verification protocol for pulsed dose‐rate (PDR) brachytherapy based on in vivo time‐resolved (1 s time resolution) fiber‐coupled luminescence dosimetry.Methods:Five cervix cancer patients undergoing PDR brachytherapy (Varian GammaMed Plus with) were monitored. The treatments comprised from 10 to 50 pulses (1 pulse/h) delivered by intracavitary/interstitial applicators (tandem‐ring systems and/or needles). For each patient, one or two dosimetry probes were placed directly in or close to the tumor region using stainless steel or titanium needles. Each dosimeter probe consisted of a small aluminum oxide crystal attached to an optical fiber cable (1 mm outer diameter) that could guide radioluminescence (RL) and optically stimulated luminescence (OSL) from the crystal to special readout instrumentation. Positioning uncertainty and hypothetical dose‐delivery errors (interchanged guide tubes or applicator movements from ±5 to ±15 mm) were simulated in software in order to assess the ability of the system to detect errors.Results:For three of the patients, the authors found no significant differences for comparisons between in vivo measurements and calculated reference values at the level of dose per dwell position, dose per applicator, or total dose per pulse. The standard deviations of the dose per pulse were less than 3%, indicating a stable dose delivery and a highly stable geometry of applicators and dosimeter probes during the treatments. For the two other patients, the authors noted significant deviations for three individual pulses and for one dosimeter probe. These deviations could have been due to applicator movement during the treatment and one incorrectly positioned dosimeter probe, respectively. Computer simulations showed that the likelihood of detecting a pair of interchanged guide tubes increased by a factor of 10 or more for the considered patients when going from integrating to time‐resolved dose verification. The likelihood of detecting a ±15 mm displacement error increased by a factor of 1.5 or more.Conclusions:In vivo fiber‐coupled RL/OSL dosimetry based on detectors placed in standard brachytherapy needles was demonstrated. The time‐resolved dose‐rate measurements were found to provide a good way to visualize the progression and stability of PDR brachytherapy dose delivery, and time‐resolved dose‐rate measurements provided an increased sensitivity for detection of dose‐delivery errors compared with time‐integrated dosimetry.
Longitudinal study using a diode phantom for helical tomotherapy IMRT QA
Authors: Geurts M. , Gonzalez J. , Serrano‐Ojeda P. 
Published: October 2009

Purpose:The Caribbean Radiation Oncology Center acquired a DELTA4® diode phantom for helical tomotherapy IMRT QA and presents the results of their first 264 clinical cases.Methods:The validation consisted of several case studies comparing existing ionization chamber and Gafchromic film IMRT QA results to diode phantom results, along with a longitudinal study analyzing the IMRT QA results against other machine QA procedures for a complete sample of IMRT patients.Results:The case studies resulted in a maximum observed difference of 0.7% between the diode phantom and the ionization chamber measurements in low dose‐gradient regions. Over the longitudinal study, every IMRT QA plan passed a gamma specification of a 3%/3 mm and 98% of the diodes yielded a value of less than 1. In addition, the mean 90% isodose absolute difference for all plans was 0.05% with a (1σ) standard deviation of 1.19%.Conclusions:The phantom measurements closely match the planned dose distributions in high and low dose‐gradient regions. In addition, a significant positive statistical correlation was determined between the IMRT QA, daily QA, and rotational variation output measurements. Together, these results signify high degree of accuracy of both the DELTA4 phantom as well as the TomoTherapy® Hi‐Art® system.
Treatment planning for volumetric modulated arc therapy
Authors: Bedford James L. 
Published: October 2009

Purpose: Volumetric modulated arc therapy (VMAT) is a specific type of intensity‐modulated radiation therapy (IMRT) in which the gantry speed, multileaf collimator (MLC) leaf position, and dose rate vary continuously during delivery. A treatment planning system for VMAT is presented.Methods: Arc control points are created uniformly throughout one or more arcs. An iterative least‐squares algorithm is used to generate a fluence profile at every control point. The control points are then grouped and all of the control points in a given group are used to approximate the fluence profiles. A direct‐aperture optimization is then used to improve the solution, taking into account the allowed range of leaf motion of the MLC. Dose is calculated using a fast convolution algorithm and the motion between control points is approximated by 100 interpolated dose calculation points. The method has been applied to five cases, consisting of lung, rectum, prostate and seminal vesicles, prostate and pelvic lymph nodes, and head and neck. The resulting plans have been compared with segmental (step‐and‐shoot) IMRT and delivered and verified on an Elekta Synergy to ensure practicality.Results:For the lung, prostate and seminal vesicles, and rectum cases, VMAT provides a plan of similar quality to segmental IMRT but with faster delivery by up to a factor of 4. For the prostate and pelvic nodes and head‐and‐neck cases, the critical structure doses are reduced with VMAT, both of these cases having a longer delivery time than IMRT. The plans in general verify successfully, although the agreement between planned and measured doses is not very close for the more complex cases, particularly the head‐and‐neck case.Conclusions:Depending upon the emphasis in the treatment planning, VMAT provides treatment plans which are higher in quality and/or faster to deliver than IMRT. The scheme described has been successfully introduced into clinical use.
Initial investigation on the use of MR spectroscopy and micro‐MRI of GAFCHROMIC® EBT radiotherapy film
Authors: Holly Rick , Keller Brian M. , Pignol Jean‐Philippe , Lemaire Claude , Peemoeller Hartwig 
Published: October 2009

Purpose:This article presents an initial investigation of the efficacy of using MRS and micro‐MRI as analysis techniques for irradiated GAFCHROMIC EBT® radiotherapy films.Methods:GAFCHROMIC® EBT radiotherapy film was irradiated with 6 MV x rays to known doses ranging from 5 to 1000 cGy. 24 h following irradiation MRS measurements were performed to access the degree of post‐irradiation polymer cross‐linking. 2D micro‐MRI experiments were also performed for film irradiations of 0 and 300 cGy.Results:Linear response of the MRS linewidth to dose in the range from 0 to 400 cGy was observed. Such linearity is not seen when analyzed under conventional light analysis. The sensitivity of the film, as measured by the slope of the curve between 0 and 400 cGy, is , demonstrating the sensitivity of the MRS technique used to analyze the film. The film saturates at a dose of approximately 900 cGy. Broadline MRS provides a quantitative measure of the degree of polymerization of the film.Conclusions:A quantitative measurement of the degree of polymerization of GAFCHROMIC® EBT film has been presented using MRS. The saturation of the film at approximately 900 cGy is corroborated by that observed with light analysis. Further MR spectroscopic experiments are needed to investigate the response of the film to dose, allowing for a better understanding of the relationship between polymer cross‐linking in the active layer.
Uncluttered single‐image visualization of the abdominal aortic vessel tree: Method and evaluation
Authors: Won Joong‐Ho , Rosenberg Jarrett , Rubin Geoffrey D. , Napel Sandy 
Published: October 2009

Purpose:The authors develop a method to visualize the abdominal aorta and its branches, obtained by CT or MR angiography, in a single 2D stylistic image without overlap among branches.Methods:The abdominal aortic vasculature is modeled as an articulated object whose underlying topology is a rooted tree. The inputs to the algorithm are the 3D centerlines of the abdominal aorta, its branches, and their associated diameter information. The visualization problem is formulated as an optimization problem that finds a spatial configuration of the bounding boxes of the centerlines most similar to the projection of the input into a given viewing direction (e.g., anteroposterior), while not introducing intersections among the boxes. The optimization algorithm minimizes a score function regarding the overlap of the bounding boxes and the deviation from the input. The output of the algorithm is used to produce a stylistic visualization, made of the 2D centerlines modulated by the associated diameter information, on a plane. The authors performed a preliminary evaluation by asking three radiologists to label 366 arterial branches from the 30 visualizations of five cases produced by the method. Each of the five patients was presented in six different variant images, selected from ten variants with the three lowest and three highest scores. For each label, they assigned confidence and distortion ratings (low/medium/high). They studied the association between the quantitative metrics measured from the visualization and the subjective ratings by the radiologists.Results:All resulting visualizations were free from branch overlaps. Labeling accuracies of the three readers were 93.4%, 94.5%, and 95.4%, respectively. For the total of 1098 samples, the distortion ratings were low: 77.39%, medium: 10.48%, and high: 12.12%. The confidence ratings were low: 5.56%, medium: 16.50%, and high: 77.94%. The association study shows that the proposed quantitative metrics can predict a reader's subjective ratings and suggests that the visualization with the lowest score should be selected for readers.Conclusions:The method for eliminating misleading false intersections in 2D projections of the abdominal aortic tree conserves the overall shape and does not diminish accurate identifiability of the branches.
Image‐based iterative compensation of motion artifacts in computed tomography
Authors: Schretter Colas , Rose Georg , Bertram Matthias 
Published: October 2009

Purpose:This article presents an iterative method for compensation of motion artifacts for slowly rotating computed tomography (CT) systems. Patient's motion introduces inconsistencies among projections and yields severe reconstruction artifacts for free‐breathing acquisitions. Streaks and doubling of structures can appear and the resolution is limited by strong blurring.Methods:The rationale of the proposed motion compensation method is to iteratively correct the reconstructed image by first decomposing the perceived motion in projection space, then reconstructing the motion artifacts in image space, and finally subtracting the artifacts from an initial image. The initial image is reconstructed from the acquired data and might contain motion blur artifacts but, nevertheless, is considered as a reference for estimating the reconstruction artifacts.Results:Qualitative and quantitative figures are shown for experiments based on numerically simulated projections of a sequence of clinical images resulting from a respiratory‐gated helical CT acquisition. The border of the diaphragm becomes progressively sharper and the contrast improves for small structures in the lungs.Conclusions:The originality of the technique stems from the fact that the patient motion is not explicitly estimated but the motion artifacts are reconstructed in image space. This approach could provide sharp static anatomical images on interventional C‐arm systems or on slowly rotating X‐ray equipments in radiotherapy.
Clinical implementation of a digital tomosynthesis‐based seed reconstruction algorithm for intraoperative postimplant dose evaluation in low dose rate prostate brachytherapy
Authors: Brunet‐Benkhoucha Malik , Verhaegen Frank , Lassalle Stéphanie , Béliveau‐Nadeau Dominic , Reniers Brigitte , Donath David , Taussky Daniel , Carrier Jean‐François 
Published: October 2009

Purpose:The low dose rate brachytherapy procedure would benefit from an intraoperative postimplant dosimetry verification technique to identify possible suboptimal dose coverage and suggest a potential reimplantation. The main objective of this project is to develop an efficient, operator‐free, intraoperative seed detection technique using the imaging modalities available in a low dose rate brachytherapy treatment room.Methods:This intraoperative detection allows a complete dosimetry calculation that can be performed right after an I‐125 prostate seed implantation, while the patient is still under anesthesia. To accomplish this, a digital tomosynthesis‐based algorithm was developed. This automatic filtered reconstruction of the 3D volume requires seven projections acquired over a total angle of 60° with an isocentric imaging system.Results:A phantom study was performed to validate the technique that was used in a retrospective clinical study involving 23 patients. In the patient study, the automatic tomosynthesis‐based reconstruction yielded seed detection rates of 96.7% and 2.6% false positives. The seed localization error obtained with a phantom study is. The average time needed for reconstruction is below 1 min. The reconstruction algorithm also provides the seed orientation with an uncertainty of . The seed detection algorithm presented here is reliable and was efficiently used in the clinic.Conclusions:When combined with an appropriate coregistration technique to identify the organs in the seed coordinate system, this algorithm will offer new possibilities for a next generation of clinical brachytherapy systems.
Characterization of free breathing patterns with 5D lung motion model
Authors: Zhao Tianyu , Lu Wei , Yang Deshan , Mutic Sasa , Noel Camille E. , Parikh Parag J. , Bradley Jeffrey D. , Low Daniel A. 
Published: October 2009

Purpose:To determine the quiet respiration breathing motion model parameters for lung cancer and nonlung cancer patients.Methods:49 free breathing patient 4DCT image datasets (25 scans, cine mode) were collected with simultaneous quantitative spirometry. A cross‐correlation registration technique was employed to track the lung tissue motion between scans. The registration results were applied to a lung motion model: , where is the position of a piece of tissue located at reference position during a reference breathing phase (zero tidal volume , zero airflow ). is a parameter that characterizes the motion due to air filling (motion as a function of tidal volume ) and is the parameter that accounts for the motion due to the imbalance of dynamical stress distributions during inspiration and exhalation that causes lung motion hysteresis (motion as a function of airflow ). The parameters and together provide a quantitative characterization of breathing motion that inherently includes the complex hysteresis interplay. The and distributions were examined for each patient to determine overall general patterns and interpatient pattern variations.Results:For 44 patients, the greatest values of were observed in the inferior and posterior lungs. For the rest of the patients, reached its maximum in the anterior lung in three patients and the lateral lung in two patients. The hysteresis motion had greater variability, but for the majority of patients, was largest in the lateral lungs.Conclusions:This is the first report of the three‐dimensional breathing motion model parameters for a large cohort of patients. The model has the potential for noninvasively predicting lung motion. The majority of patients exhibited similar maps and the maps showed greater interpatient variability. The motion parameter interpatient variability will inform our need for custom radiation therapy motion models. The utility of this model depends on the parameter stability over time, which is still under investigation.
Implementation and characterization of a 320‐slice volumetric CT scanner for simulation in radiation oncology
Authors: Coolens C. , Breen S. , Purdie T. G. , Owrangi A. , Publicover J. , Bartolac S. , Jaffray D. A. 
Published: October 2009

Purpose:Effective target definition and broad employment of treatment response assessment with dynamic contrast‐enhanced CT in radiation oncology requires increased speed and coverage for use within a single bolus injection. To this end, a novel volumetric CT scanner (Aquilion One, Toshiba, Tochigi Pref., Japan) has been installed at the Princess Margaret Hospital for implementation into routine CT simulation. This technology offers great advantages for anatomical and functional imaging in both scan speed and coverage. The aim of this work is to investigate the system's imaging performance and quality as well as CT quantification accuracy which is important for radiotherapy dose calculations.Methods:The 320‐slice CT scanner uses a wide‐area (2D) solid‐state detector design which provides the possibility to acquire a volumetric axial length of without moving the CT couch. This is referred to as “volume” and can be scanned with a rotation speed of . The scanner can also be used as a 64‐slice CT scanner and perform conventional (axial) and helical acquisitions with collimation ranges of 1–32 and , respectively. Commissioning was performed according to AAPM Reports TG 66 and 39 for both helical and volumetric imaging. Defrise and other cone‐beam image analysis tests were performed.Results:Overall, the imaging spatial resolution and geometric efficiency (GE) were found to be very good (, spatial integrity and ) and within the AAPM guidelines as well as IEC recommendations. Although there is evidence of some cone‐beam artifacts when scanning the Defrise phantom, image quality was found to be good and sufficient for treatment planning (soft tissue noise ). Measurements of CT number stability and contrast‐to‐noise values across the volume indicate clinically acceptable scan accuracy even at the field edge.Conclusions:Initial experience with this exciting new technology confirms its accuracy for routine CT simulation within radiation oncology and allows for future investigations into specialized dynamic volumetric imaging applications.
Time dependence of energy spectra of brachytherapy sources and its impact on the half and the tenth value layers
Authors: Yue Ning J. , Chen Zhe , Hearn Robert A. , Rodgers Joseph J. , Nath Ravinder 
Published: October 2009

Purpose:Several factors including radionuclide purity influence the photon energy spectra from sealed brachytherapy sources. The existence of impurities and trace elements in radioactive materials as well as the substrate and encapsulation may not only alter the spectrum at a given time but also cause change in the spectra as a function of time. The purpose of this study is to utilize a semiempirical formalism, which quantitatively incorporates this time dependence, to calculate and evaluate the shielding requirement impacts introduced by this time dependence for a source.Methods:The formalism was used to calculate the thicknesses in lead for a model 200 seed. Prior to 2005, the in this source was purified to a level better than 0.006% of the total activity, the key trace impurity consisting of . Because emits higher energy photons and has a much longer half‐life of compared to , its presence in seeds led to a time dependence of the photon spectrum and other related physical quantities. This study focuses on the time dependence of the NthVL and the analysis of the corresponding shielding requirements.Results:The results indicate that the first HVL and the first TVL in lead steadily increased with time for about and then reached a plateau. The increases at plateau were more than 1000 times compared to the corresponding values on the zeroth day. The second and third TVLs in lead reached their plateaus in about 100 and , respectively, and the increases were about 19 and 2.33 times the corresponding values on the zeroth day, respectively. All the TVLs demonstrated a similar time dependence pattern, with substantial increases and eventual approach to a plateau.Conclusions:The authors conclude that the time dependence of the emitted photon spectra from brachytherapy sources can introduce substantial variations in the values of the with time if certain impurities are present. The contribution of to the dose rate constant was less than 0.03% in the earlier seeds, and because of the use of new processing technologies since 2005, this impurity has been essentially eliminated, as demonstrated in the measured spectra of current model 200 seeds. This study illustrates the importance of performing photon spectroscopy of the manufactured radioactive sources as a quality assurance test for an assessment over time of both the radiation protection and the dosimetric properties.