bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of nonlinear ultrasound propagation on high intensity brain therapy
Authors: Pinton Gianmarco , Aubry Jean‐Francois , Fink Mathias , Tanter Mickael 
Published: March 2011

Purpose:As an ultrasound wave propagates nonlinearly, energy is transferred to higher frequencies where it is more strongly attenuated. Compared to soft tissue, the skull has strongly heterogeneous material parameters. The authors characterize with experiments and establish a numerical method that can describe the effects of the skull on the nonlinear components of ultrasonic wave propagation for application to high intensity focused ultrasound (HIFU) therapy in the brain. The impact of nonlinear acoustic propagation on heat deposition and thermal dose delivery is quantified and compared to linear assumptions by coupling an acoustic simulation with a heating model for brain tissue.Methods:A degassed dessicated human skull was placed in a water tank and insonified at 1 MPa with 7 mm transducer from a custom array designed for HIFU treatment. Two dimensional scans were performed preceding and following propagation through the skull with a calibrated hydrophone. Data from the scan preceding the skull were used as an input to a three dimensional finite difference time domain (FDTD) simulation that calculates the effects of diffraction, density, attenuation with linear dependence on frequency via relaxation mechanisms, and second order nonlinearity. A measured representation of the skull was used to determine the skull's acoustic properties. The validated acoustic model was used to determine the loss due to nonlinear propagation and then coupled to a finite difference simulation of the bioheat equation for two focal configurations at 3 and 7.5 cm from the skull surface.Results:Prior to propagation through the skull, the second harmonic component was 19 dB lower than the fundamental, and the third harmonic component was 37 dB lower. Following the skull, the second harmonic component was 35 dB lower and the third harmonic was 55 dB lower. The simulation is in agreement with the measurements to within 0.5 dB across the considered frequency range and shows good agreement across the two dimensional scan. It is then shown that the volume of treated brain is at least twice as large when assuming nonlinear acoustics.Conclusions:The authors have established a three dimensional FDTD simulation that accurately models the effects of nonlinearity and attenuation for propagation through the skull. Experimental validation shows good agreement across a broad frequency range and spatial extent. The nonlinear thermal dose was over an order of magnitude larger at the focus than the linear thermal dose and the necrotic volume was larger by at least a factor of 2. These results have particular applications to treatment planning.
Fast, limited‐data photoacoustic imaging for multiplexed systems using a frequency‐domain estimation technique
Authors: Gamelin John K. , Aguirre Andres , Zhu Quing 
Published: March 2011

Purpose:A new frequency‐domain estimation algorithm has been developed that usesa priori information to simultaneously improve imaging quality and time resolution in photoacoustic tomography with incomplete data sets.Methods:The method involves application of a single‐stage Wiener optimal filter to augment data sets by interpolation between measurement locations using relationships determined in a reference scan. The filter can be applied in real‐time using FFT methods using either fixed or dynamic references and used with any imaging algorithm. The performance of the method is compared to a modified version of constrained backprojection algorithms using simulations and experimental investigations.Results:Simulations demonstrate the effectiveness of the approach for tracking dynamic photoacoustic activity for data sets with limited views (90°) or tomographic views with a reduced number of acquisition angles at any given time. Experimental data of contrast uptake and washout using a 512‐element curved transducer with 8:1 electronic multiplexing with the algorithm demonstrate full two‐dimensional tomographic imaging with a temporal resolution better than 130 ms.Conclusions:The estimation algorithm enables high spatial resolution, real‐time imaging of dynamic physiological events or volumetric regions for photoacoustic systems employing multiplexing or scanning.
CT effective dose per dose length product using ICRP 103 weighting factors
Authors: Huda Walter , Magill Dennise , He Wenjun 
Published: March 2011

Purpose:To generate effective dose per unit dose length product (E/DLP) conversion factors incorporating ICRP Publication 103 tissue weighting factors.Methods:Effective doses for CT examinations were obtained using theIMPACT Dosimetry Calculator using all 23 dose data sets that are offered by this spreadsheet. CT examinations were simulated for scans performed along the patient long axis for each dosimetry data set using a 4 cm beam width ranging from the upper thighs to top of the head. Five basic body regions (head, neck, chest, abdomen, and pelvis), as well as combinations of the regions (head/neck, chest/abdomen, abdomen/pelvis, and chest/abdomen/pelvis) and whole body CT scans were investigated. Correction factors were generated that can be applied to convert E/DLP conversion factors based on ICRP 60 data to conversion factors that are valid for ICRP 103 data (i.e., ).Results:Use of ICRP 103 weighting factors increase effective doses for head scans by, for chest scans by , and decrease effective doses for pelvis scans by . Current E/DLP conversion factors are estimated to be for head CT examinations and range between 14 and for body CT examinations.Conclusions:Factors that enable patient CT doses to be adjusted to account for ICRP 103 tissue weighting factors are provided, which result in E/DLP factors that were increased in head and chest CT, reduced in pelvis CT, and showed no marked change in neck and abdomen CT.
Four‐dimensional computed tomography pulmonary ventilation images vary with deformable image registration algorithms and metrics
Authors: Yamamoto Tokihiro , Kabus Sven , Klinder Tobias , von Berg Jens , Lorenz Cristian , Loo Billy W. , Keall Paul J. 
Published: March 2011

Purpose:A novel pulmonary ventilation imaging technique based on four‐dimensional (4D) CT has advantages over existing techniques and could be used for functional avoidance in radiotherapy. There are various deformable image registration (DIR) algorithms and two classes of ventilation metric that can be used for 4D‐CT ventilation imaging, each yielding different images. The purpose of this study was to quantify the variability of the 4D‐CT ventilation to DIR algorithms and metrics.Methods:4D‐CT ventilation images were created for 12 patients using different combinations of two DIR algorithms, volumetric and surface‐based , yielding two displacement vector fields (DVFs) per patient ( and ), and two metrics, Hounsfield unit (HU) change and Jacobian determinant of deformation , yielding four ventilation image sets (, , , and ). First, and were compared visually and quantitatively to the length of 3D displacement vector difference. Second, four ventilation images were compared based on voxel‐based Spearman's rank correlation coefficients and coefficients of variation as a measure of spatial heterogeneity. was chosen as the reference for the comparison.Results:The mean length of 3D vector difference between and was on average, which was smaller than the voxel dimension of the image set and the variations. Visually, the reference demonstrated similar regional distributions with ; the reference, however, was markedly different from and . The correlation coefficients of with , , and were , , and , respectively, indicating that the metric introduced larger variations in the ventilation images than the DIR algorithm. The spatial heterogeneities for , , , and were , , , and , respectively, also demonstrating that the metric introduced larger variations.Conclusions:4D‐CT pulmonary ventilation images vary widely with DIR algorithms and metrics. Careful physiologic validation to determine the appropriate DIR algorithm and metric is needed prior to its applications.
Accounting for the tongue‐and‐groove effect using a robust direct aperture optimization approach
Authors: Salari Ehsan , Men Chunhua , Romeijn H. Edwin 
Published: March 2011

Purpose:Traditionally, the tongue‐and‐groove effect due to the multileaf collimator architecture in intensity‐modulated radiation therapy (IMRT) has typically been deferred to the leaf sequencing stage. The authors propose a new direct aperture optimization method for IMRT treatment planning that explicitly incorporates dose calculation inaccuracies due to the tongue‐and‐groove effect into the treatment plan optimization stage.Methods:The authors avoid having to accurately estimate the dosimetric effects of the tongue‐and‐groove architecture by using lower and upper bounds on the dose distribution delivered to the patient. They then develop a model that yields a treatment plan that is robust with respect to the corresponding dose calculation inaccuracies.Results:Tests on a set of ten clinical head‐and‐neck cancer cases demonstrate the effectiveness of the new method in developing robust treatment plans with tight dose distributions in targets and critical structures. This is contrasted with the very loose bounds on the dose distribution that are obtained by solving a traditional treatment plan optimization model that ignores tongue‐and‐groove effects in the treatment planning stage.Conclusions:A robust direct aperture optimization approach is proposed to account for the dosimetric inaccuracies caused by the tongue‐and‐groove effect. The experiments validate the ability of the proposed approach in designing robust treatment plans regardless of the exact consequences of the tongue‐and‐groove architecture.
The difference of scoring dose to water or tissues in Monte Carlo dose calculations for low energy brachytherapy photon sources
Authors: Landry Guillaume , Reniers Brigitte , Pignol Jean‐Philippe , Beaulieu Luc , Verhaegen Frank 
Published: March 2011

Purpose:The goal of this work is to compare (radiation transported in medium; dose scored in medium) and (radiation transported in medium; dose scored in water) obtained from Monte Carlo (MC) simulations for a subset of human tissues of interest in low energy photon brachytherapy. Using low dose rate seeds and an electronic brachytherapy source (EBS), the authors quantify the large cavity theory conversion factors required. The authors also assess whether applying large cavity theory utilizing the sources' initial photon spectra and average photon energy induces errors related to spatial spectral variations. First, ideal spherical geometries were investigated, followed by clinical brachytherapy LDR seed implants for breast and prostate cancer patients.Methods:Two types of dose calculations are performed with theGEANT4 MC code. (1) For several human tissues, dose profiles are obtained in spherical geometries centered on four types of low energy brachytherapy sources: , , and seeds, as well as an EBS operating at 50 kV. Ratios of over are evaluated in the 0–6 cm range. In addition to mean tissue composition, compositions corresponding to one standard deviation from the mean are also studied. (2) Four clinical breast (using ) and prostate (using ) brachytherapy seed implants are considered. MC dose calculations are performed based on postimplant CT scans using prostate and breast tissue compositions. PTV values are compared for and .Results:(1) Differences of −3% to 70% are observed for the investigated tissues. For a given tissue, is similar for all sources within 4% and does not vary more than 2% with distance due to very moderate spectral shifts. Variations of tissue composition about the assumed mean composition influence the conversion factors up to 38%. (2) The ratio of over for clinical implants matches at 1 cm from the single point sources.Conclusions:Given the small variation with distance, using conversion factors based on the emitted photon spectrum (or its mean energy) of a given source introduces minimal error. The large differences observed between scoring schemes underline the need for guidelines on choice of media for dose reporting. Providing such guidelines is beyond the scope of this work.
Interior region‐of‐interest reconstruction using a small, nearly piecewise constant subregion
Authors: Taguchi Katsuyuki , Xu Jingyan , Srivastava Somesh , Tsui Benjamin M. W. , Cammin Jochen , Tang Qiulin 
Published: March 2011

Purpose:To develop a method to reconstruct an interior region‐of‐interest (ROI) image with sufficient accuracy that uses differentiated backprojection (DBP) projection onto convex sets (POCS) [H. Kudo et al., “Tiny a priori knowledge solves the interior problem in computed tomography,” Phys. Med. Biol., – (2008)] and a tiny knowledge that there exists a nearly piecewise constant subregion.Methods:The proposed method first employs filtered backprojection to reconstruct an image on which a tiny region with a small variation in the pixel values is identified inside the ROI. Total variation minimization [H. Yu and G. Wang, “Compressed sensing based interior tomography,” Phys. Med. Biol., – (2009); W. Han et al., “A general total variation minimization theorem for compressed sensing based interior tomography,” Int. J. Biomed. Imaging, Article (2009)] is then employed to obtain pixel values in the subregion , which serve as a priori knowledge in the next step. Finally, DBP‐POCS is performed to reconstruct inside the ROI. Clinical data and the reconstructed image obtained by an x‐ray computed tomography system (SOMATOM Definition; Siemens Healthcare) were used to validate the proposed method. The detector covers an object with a diameter of . The projection data were truncated either moderately to limit the detector coverage to of the object or severely to cover . Images were reconstructed using the proposed method.Results:The proposed method provided ROI images with correct pixel values in all areas except near the edge of the ROI. The coefficient of variation, i.e., the root mean square error divided by the mean pixel values, was less than 2.0% or 4.5% with the moderate or severe truncation cases, respectively, except near the boundary of the ROI.Conclusions:The proposed method allows for reconstructing interior ROI images with sufficient accuracy with a tiny knowledge that there exists a nearly piecewise constant subregion.
Experience of micromultileaf collimator linear accelerator based single fraction stereotactic radiosurgery: Tumor dose inhomogeneity, conformity, and dose fall off
Authors: Hong Linda X. , Garg Madhur , Lasala Patrick , Kim Mimi , Mah Dennis , Chen Chin‐Cheng , Yaparpalvi Ravindra , Mynampati Dinesh , Kuo Hsiang‐Chi , Guha Chandan , Kalnicki Shalom 
Published: March 2011

Purpose:Sharp dose fall off outside a tumor is essential for high dose single fraction stereotactic radiosurgery (SRS) plans. This study explores the relationship among tumor dose inhomogeneity, conformity, and dose fall off in normal tissues for micromultileaf collimator (mMLC) linear accelerator (LINAC) based cranial SRS plans.Methods:Between January 2007 and July 2009, 65 patients with single cranial lesions were treated with LINAC‐based SRS. Among them, tumors had maximum diameters: 31; between 20 and 30 mm: 21; and : 13. All patients were treated with 6 MV photons on a Trilogy® linear accelerator (Varian Medical Systems, Palo Alto, CA) with a tertiary m3® high‐resolution mMLC (Brainlab, Feldkirchen, Germany), using either noncoplanar conformal fixed fields or dynamic conformal arcs. The authors also created retrospective study plans with identical beam arrangement as the treated plan but with different tumor dose inhomogeneity by varying the beam margins around the planning target volume (PTV). All retrospective study plans were normalized so that the minimum PTV dose was the prescription dose (PD). Isocenter dose, mean PTV dose, RTOG conformity index (CI), RTOG homogeneity index (HI), dose gradient index (defined as the difference between equivalent sphere radius of 50% isodose volume and prescription isodose volume), and normal tissue volume (as a ratio to PTV volume) receiving 50% prescription dose were calculated.Results:HI was inversely related to the beam margins around the PTV. CI had a “V” shaped relationship with HI, reaching a minimum when HI was approximately 1.3. Isocenter dose and mean PTV dose (as percentage of PD) increased linearly with HI. and initially declined with HI and then reached a plateau when HI was approximately 1.3. These trends also held when tumors were grouped according to their maximum diameters. The smallest tumor group (maximum diameters ) had the most HI dependence for dose fall off. For treated plans, CI averaged with HI ; the average was , , and , respectively, for tumors , between 20 and 30 mm, and .Conclusions:Tumor dose inhomogeneity can be used as an important and convenient parameter to evaluate mMLC LINAC‐based SRS plans. Sharp dose fall off in the normal tissue is achieved with sufficiently high tumor dose inhomogeneity. By adjusting beam margins, a homogeneity index of approximately 1.3 would provide best conformity for the authors' SRS system.
Low‐dose cardio‐respiratory phase‐correlated cone‐beam micro‐CT of small animals
Authors: Sawall Stefan , Bergner Frank , Lapp Robert , Mronz Markus , Karolczak Marek , Hess Andreas , Kachelrieß Marc 
Published: March 2011

Purpose:Micro‐CT imaging of animal hearts typically requires a double gating procedure because scans during a breath‐hold are not possible due to the long scan times and the high respiratory rates. Simultaneous respiratory and cardiac gating can either be done prospectively or retrospectively. True five‐dimensional information can be either retrieved with retrospective gating or with prospective gating if several prospective gates are acquired. In any case, the amount of information available to reconstruct one volume for a given respiratory and cardiac phase is orders of magnitude lower than the total amount of information acquired. For example, the reconstruction of a volume from a 10% wide respiratory and a 20% wide cardiac window uses only 2% of the data acquired. Achieving a similar image quality as a nongated scan would therefore require to increase the amount of data and thereby the dose to the animal by up to a factor of 50.Methods:To achieve the goal of low‐dose phase‐correlated (LDPC) imaging, the authors propose to use a highly efficient combination of slightly modified existing algorithms. In particular, the authors developed a variant of the McKinnon–Bates image reconstruction algorithm and combined it with bilateral filtering in up to five dimensions to significantly reduce image noise without impairing spatial or temporal resolution.Results:The preliminary results indicate that the proposed LDPC reconstruction method typically reduces image noise by a factor of up to 6 (e.g., from 170 to 30 HU), while the dose values lie in a range from 60 to 500 mGy. Compared to other publications that apply 250–1800 mGy for the same task [C. T. Badea et al., “4D micro‐CT of the mouse heart,” Mol. Imaging (), – (2005); M. Drangova et al., “Fast retrospectively gated quantitative four‐dimensional (4D) cardiac micro computed tomography imaging of free‐breathing mice,” Invest. Radiol. (), – (2007); S. H. Bartling et al., “Retrospective motion gating in small animal CT of mice and rats,” Invest. Radiol. (), – (2007)], the authors' LDPC approach therefore achieves a more than tenfold dose usage improvement.Conclusions:The LDPC reconstruction method improves phase‐correlated imaging from highly undersampled data. Artifacts caused by sparse angular sampling are removed and the image noise is decreased, while spatial and temporal resolution are preserved. Thus, the administered dose per animal can be decreased allowing for long term studies with reduced metabolic inference.
Treatment planning of a skin‐sparing conical breast brachytherapy applicator using conventional brachytherapy software
Authors: Yang Yun , Melhus Christopher S. , Sioshansi Shirin , Rivard Mark J. 
Published: March 2011

Purpose:AccuBoost is a noninvasive image‐guided technique for the delivery of partial breast irradiation to the tumor bed and currently serves as an alternate to conventional electron beam boost. To irradiate the target volume while providing dose sparing to the skin, the round applicator design was augmented through the addition of an internally truncated conical shield and the reduction of the source to skin distance.Methods:Brachytherapy dose distributions for two types of conical applicators were simulated and estimated using Monte Carlo (MC) methods for radiation transport and a conventional treatment planning system (TPS). MC‐derived and TPS‐generated dose volume histograms (DVHs) and dose distribution data were compared for both the conical and round applicators for benchmarking purposes.Results:Agreement using the gamma‐index test was ⩾99.95% for distance to agreement and dose accuracy criteria of 2 mm and 2%, respectively. After observing good agreement, TPS DVHs and dose distributions for the conical and round applicators were obtained and compared. Brachytherapy dose distributions generated using Pinnacle3 for ten CT data sets showed that the parallel‐opposed beams of the conical applicators provided similar PTV coverage to the round applicators and reduced the maximum dose to skin, chest wall, and lung by up to 27%, 42%, and 43%, respectively.Conclusions:Brachytherapy dose distributions for the conical applicators have been generated using MC methods and entered into the Pinnacle3 TPS via the Tufts technique. Treatment planning metrics for the conical AccuBoost applicators were significantly improved in comparison to those for conventional electron beam breast boost.
Tolerance levels of EPID‐based quality control for volumetric modulated arc therapy
Authors: Jørgensen M. K. , Hoffmann L. , Petersen J. B. B. , Præstegaard L. H. , Hansen R. , Muren L. P. 
Published: March 2011

Purpose:Volumetric modulated arc therapy (VMAT) includes features such as a variable dose rate and gantry speed in addition to the beam modulation achieved with multileaf collimator (MLC) motion patterns employed in intensity modulated radiotherapy. Three tests have previously been proposed for the evaluation of the performance of VMAT delivery. In order to enable a convenient and accurate routine machine quality control (QC) program, the present study proposes tolerance levels for these tests based on a department‐wide implementation of an electronic portal imaging device (EPID)‐based QC.Methods:Three different VMAT tests—a picket fence (PF) test, a dose rate versus gantry speed (DRGS) test, and a dose rate versus MLC leaf speed (DRMLC) test—were performed on nine accelerators using two different EPIDs (aS1000 and aS500, Varian Medical Systems). All tests were repeated six times for each accelerator. The images were analyzed using an in‐house‐developed software. For the PF test, the positions and widths of individual MLC leaf gaps were compared to the mean value. In the DRGS and DRMLC tests, different combinations of dose rate, gantry speed, and MLC leaf speed were used to deliver identical doses to separate parts of the EPID. The tests were evaluated by looking for deviations in the constancy of the measured dose for the preset combinations of dose rate, gantry speed, and MLC leaf speed.Results:For the PF test, a 0.3 mm tolerance level was suggested for the positioning of the MLC leaves. The tolerance level for the gap width was 0.5 mm. For the DRGS and DRMLC tests, a 3% tolerance level was proposed.Conclusions:With the adapted levels of tolerance for an EPID‐based approach, the PF, the DRGS, and the DRMLC tests offer a convenient and accurate machine QC program for linear accelerators used for VMAT.