bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the use of a proton path probability map for proton computed tomography reconstructiona)
Authors: Wang Dongxu , Mackie T. Rockwell , Tomé Wolfgang A. 
Published: July 2010

Purpose:To describe a method to estimate the proton path in proton computed tomography (pCT) reconstruction, which is based on the probability of a proton passing through each point within an object to be imaged.Methods:Based on multiple Coulomb scattering and a semianalytically derived model, the conditional probability of a proton passing through each point within the object given its incoming and exit condition is calculated in a Bayesian inference framework, employing data obtained from Monte Carlo simulation usingGEANT4. The conditional probability at all of the points in the reconstruction plane forms a conditional probability map and can be used for pCT reconstruction.Results:From the generated conditional probability map, a most‐likely path (MLP) and a 90% probability envelope around the most‐likely path can be extracted and used for pCT reconstruction. The reconstructed pCT image using the conditional probability map yields a smooth pCT image with minor artifacts. pCT reconstructions obtained using the extracted MLP and the 90% probability envelope compare well to reconstructions employing the method of cubic spline proton path estimation.Conclusions:The conditional probability of a proton passing through each point in an object given its entrance and exit condition can be obtained using the proposed method. The extracted MLP and the 90% probability envelope match the proton path recorded in theGEANT4 simulation well. The generated probability map also provides a benchmark for comparing different path estimation methods.
The performance of steady‐state harmonic magnetic resonance elastography when applied to viscoelastic materials
Authors: Doyley Marvin M. , Perreard Irina , Patterson Adam. J. , Weaver John B. , Paulsen Keith M. 
Published: July 2010

Purpose:The clinical efficacy of breast elastography may be limited when the authors employ the assumption that soft tissues exhibit linear, frequency‐independent isotropic mechanical properties during the recovery of shear modulus. Thus, the purpose of this research was to evaluate the degradation in performance incurred when linear‐elastic MR reconstruction methods are applied to phantoms that are fabricated using viscoelastic materials.Methods:To develop phantoms with frequency‐dependent mechanical properties, the authors measured the complex modulus of two groups of cylindrical‐shaped gelatin samples over a wide frequency range (up to 1 kHz) with the established principles of time‐temperature superposition (TTS). In one group of samples, the authors added varying amounts of agar (1%–4%); in the other group, the authors added varying amounts of sucrose (2.5%–20%). To study how viscosity affected the performance of the linear‐elastic reconstruction method, the authors constructed an elastically heterogeneous MR phantom to simulate the case where small viscoelastic lesions were surrounded by relatively nonviscous breast tissue. The breast phantom contained four linear, viscoelastic spherical inclusions (10 mm diameter) that were embedded in normal gelatin. The authors imaged the breast phantom with a clinical prototype of a MRE system and recovered the shear‐modulus distribution using the overlapping‐subzone‐linear‐elastic image‐reconstruction method. The authors compared the recovered shear modulus to that measured using the TTS method.Results:The authors demonstrated that viscoelastic phantoms could be fabricated by including sucrose in the gelation process and that small viscoelastic inclusions were visible in MR elastograms recovered using a linear‐elastic MR reconstruction process; however, artifacts that degraded contrast and spatial resolution were more prominent in highly viscoelastic inclusions. The authors also established that the accuracy of the MR elastograms depended on the degree of viscosity that the inclusion exhibited.Conclusions:The results demonstrated that reconstructing shear modulus from other constitutive laws, such as viscosity, should improve both the accuracy and quality of MR elastograms of the breast.
Predictive modeling of lung motion over the entire respiratory cycle using measured pressure‐volume data, 4DCT images, and finite‐element analysis
Authors: Eom Jaesung , Xu Xie George , De Suvranu , Shi Chengyu 
Published: July 2010

Purpose:Predicting complex patterns of respiration can benefit the management of the respiratory motion for radiation therapy of lung cancer. The purpose of the present work was to develop a patient‐specific, physiologically relevant respiratory motion model which is capable of predicting lung tumor motion over a complete normal breathing cycle.Methods:Currently employed techniques for generating the lung geometry from four‐dimensional computed tomography data tend to lose details of mesh topology due to excessive surface smoothening. Some of the existing models apply displacement boundary conditions instead of the intrapleural pressure as the actual motive force for respiration, while others ignore the nonlinearity of lung tissues or the mechanics of pleural sliding. An intermediate nonuniform rational basis spline surface representation is used to avoid multiple geometric smoothing procedures used in the computational mesh preparation. Measured chest pressure‐volume relationships are used to simulate pressure loading on the surface of the model for a given lung volume, as in actual breathing. A hyperelastic model, developed from experimental observations, has been used to model the lung tissue material. Pleural sliding on the inside of the ribcage has also been considered.Results:The finite‐element model has been validated using landmarks from four patient CT data sets over 34 breathing phases. The average differences of end‐inspiration in position between the landmarks and those predicted by the model are observed to be for Patient P1, for Patient P2, for Patient P3, and for Patient P4 in the magnitude of error vector, respectively. The average errors of prediction at landmarks over multiple breathing phases in superior‐inferior direction are less than 3 mm.Conclusions:The prediction capability of pressure‐volume curve driven nonlinear finite‐element model is consistent over the entire breathing cycle. The biomechanical parameters in the model are physiologically measurable, so that the results can be extended to other patients and additional neighboring organs affected by respiratory motion.
Mechanistic formulation of a lineal‐quadratic‐linear (LQL) model: Split‐dose experiments and exponentially decaying sources
Authors: Guerrero Mariana , Carlone Marco 
Published: July 2010

Purpose:In recent years, several models were proposed that modify the standard linear‐quadratic (LQ) model to make the predicted survival curve linear at high doses. Most of these models are purely phenomenological and can only be applied in the particular case of acute doses per fraction. The authors consider a mechanistic formulation of a linear‐quadratic‐linear (LQL) model in the case of split‐dose experiments and exponentially decaying sources. This model provides a comprehensive description of radiation response for arbitrary dose rate and fractionation with only one additional parameter.Methods:The authors use a compartmental formulation of the LQL model from the literature. They analytically solve the model's differential equations for the case of a split‐dose experiment and for an exponentially decaying source. They compare the solutions of the survival fraction with the standard LQ equations and with the lethal‐potentially lethal (LPL) model.Results:In the case of the split‐dose experiment, the LQL model predicts a recovery ratio as a function of dose per fraction that deviates from the square law of the standard LQ. The survival fraction as a function of time between fractions follows a similar exponential law as the LQ but adds a multiplicative factor to the LQ parameter. The LQL solution for the split‐dose experiment is very close to the LPL prediction. For the decaying source, the differences between the LQL and the LQ solutions are negligible when the half‐life of the source is much larger than the characteristic repair time, which is the clinically relevant case.Conclusions:The compartmental formulation of the LQL model can be used for arbitrary dose rates and provides a comprehensive description of dose response. When the survival fraction for acute doses is linear for high dose, a deviation of the square law formula of the recovery ratio for split doses is also predicted.
Effects of breathing variation on gating window internal target volume in respiratory gated radiation therapya)
Authors: Cai Jing , McLawhorn Robert , Read Paul W. , Larner James M. , Yin Fang‐fang , Benedict Stanley H. , Sheng Ke 
Published: July 2010

Purpose:To investigate the effects of breathing variation on gating window internal target volume in respiratory gated radiation therapy.Method and Materials:Two‐dimensional dynamic MRI (dMRI) of lung motion was acquired in ten volunteers and eight lung cancer patients. Resorted dMRI using 4DCT acquisition method (RedCAM) was generated for selected subjects by simulating the image rebinning process. A dynamic software generated phantom (dSGP) was created by moving a solid circle (to mimic the “tumor”) with dMRI‐determined motion trajectories. The gating window internal target area (, 2D counterpart of ) was determined from both RedCAM and dSGP/dMRI. Its area , major axis , minor axis , and similarity were calculated and compared.Results:In the phantom study of 3 cm tumor, measurements of the from dSGP (, , and ) are significantly greater than those from RedCAM (, , and ). Similarly, the differences are significantly greater for the 1 cm tumor (, , and in dSGP; , , and in RedCAM). In patient studies, measurements of the from dMRI (, , and ) are also significantly greater than those from RedCAM (, , and ). Similarities were , , and in the 3 cm tumor phantom, 1 cm tumor phantom, and patient studies, respectively.Conclusion: can be underestimated by 4DCT due to breathing variations. An additional margin may be needed to account for this potential error in generating a . Cautions need to be taken when generating from 4DCT in respiratory gated radiation therapy, especially for small tumors with a large motion range .
Deformable lung registration between exhale and inhale CT scans using active cells in a combined gradient force approach
Authors: Yim Yeny , Hong Helen , Shin Yeong Gil 
Published: July 2010

Purpose:This article proposes an accurate and fast deformable registration method between end‐exhale and end‐inhale CT scans that can handle large lung deformations and accelerate the registration process.Methods:The density correction method is applied to reduce the density difference between two CT scans due to respiration and gravity. The lungs are globally aligned by affine registration and nonlinearly deformed by a demons algorithm using a combined gradient force and active cells. The use of combined gradient force allows a fast convergence in the lung regions with a weak gradient of the target image by taking into account the gradient of the source image. The use of active cells helps to accelerate the registration process and reduce the degree of deformation folding because it avoids unnecessary computation of the displacement for well‐matched lung regions.Results:The proposed method was tested with end‐exhale and end‐inhale CT scans acquired from eight normal subjects. The performance of the proposed method was evaluated through comparisons of methods that use a target gradient force or a combined gradient force, as well as methods with and without active cells. The proposed method with combined gradient force led to significantly higher accuracy compared to the method with target gradient force. For the entire lung, the proposed method provided a mean landmark error of . For the lower 30% part of the lungs, the Dice similarity coefficient and normalized cross correlation of the proposed method were higher than the original demon algorithm by 2.3% and 2.2% , respectively. The proposed method with an active cell led to fewer voxels with negative Jacobian values and a 55% decrease of processing time compared to the method without an active cell.Conclusions:The results show that the proposed method can accurately register lungs with large deformations and can considerably reduce the processing time. The proposed deformable registration technique can be used for quantitative assessments of air trapping in obstructive lung disease and for tumor motion tracking during the planning of radiotherapy treatments.
The water equivalence of solid phantoms for low energy photon beams
Authors: Hill Robin , Kuncic Zdenka , Baldock Clive 
Published: July 2010

Purpose:To compare and evaluate the dosimetric water equivalence of several commonly used solid phantoms for low energy photon beams.Methods:A total of ten different solid phantom materials was used in the study. ThePENELOPE Monte Carlo code was used to calculate depth doses and beam profiles in all the phantom materials as well as the dose to a small water voxel at the surface of the solid phantom. These doses were compared to the corresponding doses calculated in a water phantom. The primary photon beams used ranged in energy from 50 to 280 kVp.Results:A number of phantom materials had excellent agreement in dose compared to water for all the x‐ray beam energies studied. RMI457 Solid Water, Virtual Water, PAGAT, A150, and Plastic Water DT all had depth doses that agreed with those in water to within 2%. For these same phantom materials, the dose changes in the water voxel at the surface of the solid phantom were within 2%, except for A150, which agreed to within 2.7%. By comparison, the largest differences in depth doses occurred for Plastic Water (−21.7%) and polystyrene (17.6%) for the 50 kVp energy photon beam and 8 cm diameter field size. Plastic Water gave the largest difference in the normalized beam profiles with differences of up to 3.5% as compared to water. Surface dose changes, due to the presence of the solid phantom acting as the backscatter material, were found to be up to 9.1% for polystyrene with significant differences also found for Plastic Water, PMMA, and RW3 phantoms.Conclusions:The following solid phantoms can be considered water equivalent and are recommended for relative dosimetry of low energy photon beams: A150, PAGAT, Plastic Water DT, RMI457 Solid Water, and Virtual Water. However, the following solid phantoms give significant differences, compared to water, in depth doses, profiles, and/or in surface doses due to backscatter changes: Plastic Water, PMMA, polystyrene, PRESAGE, and RW3.
Measurement and verification of positron emitter nuclei generated at each treatment site by target nuclear fragment reactions in proton therapy
Authors: Miyatake Aya , Nishio Teiji , Ogino Takashi , Saijo Nagahiro , Esumi Hiroyasu , Uesaka Mitsuru 
Published: July 2010

Purpose:The purpose of this study is to verify the characteristics of the positron emitter nuclei generated at each treatment site by proton irradiation.Methods:Proton therapy using a beam on‐line PET system mounted on a rotating gantry port (BOLPs‐RGp), which the authors developed, is provided at the National Cancer Center Kashiwa, Japan. BOLPs‐RGp is a monitoring system that can confirm the activity distribution of the proton irradiated volume by detection of a pair of annihilation gamma rays coincidentally from positron emitter nuclei generated by the target nuclear fragment reactions between irradiated proton nuclei and nuclei in the human body. Activity is measured from a start of proton irradiation to a period of 200 s after the end of the irradiation. The characteristics of the positron emitter nuclei generated in a patient's body were verified by the measurement of the activity distribution at each treatment site using BOLPs‐RGp.Results:The decay curves for measured activity were able to be approximated using two or three half‐life values regardless of the treatment site. The activity of half‐life value of about 2 min was important for a confirmation of the proton irradiated volume.Conclusions:In each proton treatment site, verification of the characteristics of the generated positron emitter nuclei was performed by using BOLPs‐RGp. For the monitoring of the proton irradiated volume, the detection of generated in a human body was important.
Subtraction lung image for evaluating pulmonary ventilation in xenon‐enhanced CT
Authors: Sase Shigeru , Nakano Hideharu , Suzuki Hiroshi , Honda Mitsuru 
Published: July 2010

Purpose:The goal of this work was to develop a method of transforming a xenon‐enhanced CT (Xe‐CT) image of the lung, so as to overlap well with its baseline CT image, and creating a subtraction image (enhanced image minus baseline image), and to demonstrate the possibility of evaluating pulmonary ventilation using the subtraction image.Methods:Eight healthy menunderwent Xe‐CT lung studies. In protocol 1 for five subjects, 30% nonradioactive xenon (Xe) was inhaled for 2 min (washin) followed by air breathing for 4 min (washout). In protocol 2 for three subjects, only washin (30% Xe) for 2 min was applied. In each study, a specific range of the thorax (30 mm) in the supine position was scanned craniocaudally three times in the helical mode: At the start and end of washin and at the end of washout in protocol 1 and at 1 min intervals from the start to end of washin in protocol 2. After each study, 10‐mm‐thick CT images were reconstructed to have similar anatomical structures throughout the study. Two‐dimensional geometrical warping was performed on enhanced CT images so that they could geometrically overlap with the baseline CT image. Second to eighth degree polynomials were applied to the warping functions.Results:It was derived from the Kety model that subtraction images during washin would directly reflect pulmonary ventilation. Geometrical warping achieved an increase of 0.3%–22.0% in the area, for which ventilation could be evaluated in the subtraction image. In the cases in protocol 2 where the initial lung volume was well retained throughout the study, the ratios of the specific ventilation from the subtraction image to that from the specific ventilation map wereandfor the right and left lungs, respectively.Conclusions:A subtraction lung image during washin would provide quantitative information on pulmonary ventilation when the baseline and enhanced images could have close lung volume and these two images could overlap well. Image subtraction requires only two scans and therefore less radiation exposure compared to ordinary protocols in Xe‐CT. The proposed Xe‐CT subtraction method with the geometrical warping technique could be clinically utilized for evaluating pulmonary ventilation.
Dosimetric verification of the anisotropic analytical algorithm in lung equivalent heterogeneities with and without bone equivalent heterogeneities
Authors: Ono Kaoru , Endo Satoru , Tanaka Kenichi , Hoshi Masaharu , Hirokawa Yutaka 
Published: July 2010

Purpose: In this study, the authors evaluated the accuracy of dose calculations performed by the convolution/superposition based anisotropic analytical algorithm (AAA) in lung equivalent heterogeneities with and without bone equivalent heterogeneities.Methods: Calculations of PDDs using the AAA and Monte Carlo simulations (MCNP4C) were compared to ionization chamber measurements with a heterogeneous phantom consisting of lung equivalent and bone equivalent materials. Both 6 and 10 MV photon beams of and field sizes were used for the simulations. Furthermore, changes of energy spectrum with depth for the heterogeneous phantom using MCNP were calculated.Results: The ionization chamber measurements and MCNP calculations in a lung equivalent phantom were in good agreement, having an average deviation of only . For both 6 and 10 MV beams, the average deviation was less than 2% for the and fields in the water‐lung equivalent phantom and the field in the water‐lung‐bone equivalent phantom. Maximum deviations for the field in the lung equivalent phantom before and after the bone slab were 5.0% and 4.1%, respectively. The Monte Carlo simulation demonstrated an increase of the low‐energy photon component in these regions, more for the field compared to the field.Conclusions: The low‐energy photon by Monte Carlo simulation component increases sharply in larger fields when there is a significant presence of bone equivalent heterogeneities. This leads to great changes in the build‐up and build‐down at the interfaces of different density materials. The AAA calculation modeling of the effect is not deemed to be sufficiently accurate.
Adenovirus Targeting to Prostate-Specific Membrane Antigen through Virus-Displayed, Semirandom Peptide Library Screening
Authors: Wu Ping , Kudrolli Tarana A. , Chowdhury Wasim H. , Liu Minzhi M. , Rodriguez Ronald , Lupold Shawn E. 
Published: July 2010

Abstract
The convergence of phage-displayed peptide libraries and recombinant viral vectors launched a promising new direction in targeted viral gene therapeutics, but the translation of targeting peptides to functional cancer therapeutic agents has been challenging. Here, we report progress in developing a successful strategy to optimize targeted viral infection through adenovirus-displayed, semirandom peptide libraries. A phage-derived peptide targeting the prostate-specific membrane antigen (PSMA) was genetically incorporated into the adenoviral capsid Fiber protein and flanked by random peptide cassettes. The resulting adenovirus library was biopanned against PSMA-expressing cells and tumors to identify a PSMA-retargeted adenovirus. While the initial peptide alone could not target viral infection, the selected virus preferentially infects PSMA-expressing cells through the targeting peptide and infects LNCaP tumors after intravenous injection. Our results indicate that virus-displayed, semirandom peptide libraries can be used to optimize targeting infection. This approach represents a novel principle for developing targeted agents in a variety of disease models. Cancer Res; 70(23); 9549–53. ©2010 AACR.