bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐I‐91: Reproducibility in Prescribed Dose in AEC CT Scans Due to Table Height, Patient Size, and Localizer Acquisition Order
Authors: Winslow J , Hurwitz L , Christianson O , Samei E 
Published: July 2014

Purpose:In CT scanners, the automatic exposure control (AEC) tube current prescription depends on the acquired prescan localizer image(s). The purpose of this study was to quantify the effect that table height, patient size, and localizer acquisition order may have on the reproducibility in prescribed dose.Methods:Three phantoms were used for this study: the Mercury Phantom (comprises three tapered and four uniform regions of polyethylene 16, 23, 30, and 37 cm in diameter), acrylic sheets, and an adult anthropomorphic phantom. Phantoms were positioned per clinical protocol by our chief CT technologist or broader symmetry. Using a GE Discovery CT750HD scanner, a lateral (LAT) and posterior‐anterior (PA) localizer was acquired for each phantom at different table heights. AEC scan acquisitions were prescribed for each combination of phantom, localizer orientation, and table height; the displayed volume CTDI was recorded for each. Results were analyzed versus table height.Results:For the two largest Mercury Phantom section scans based on the PA localizer, the percent change in volume CTDI from ideal were at least 20% lower and 35% greater for table heights 4 cm above and 4 cm below proper centering, respectively. For scans based on the LAT localizer, the percent change in volume CTDI from ideal were no greater than 12% different for 4 cm differences in table height. The properly centered PA and LAT localizer‐based volume CTDI values were within 13% of each other.Conclusion:Since uncertainty in vertical patient positioning is inherently greater than lateral positioning and because the variability in dose exceeds any dose penalties incurred, the LAT localizer should be used to precisely and reproducibly deliver the intended amount of radiation prescribed by CT protocols. CT protocols can be adjusted to minimize the expected change in average patient dose.
SU‐E‐I‐93: Improved Imaging Quality for Multislice Helical CT Via Sparsity Regularized Iterative Image Reconstruction Method Based On Tensor Framelet
Authors: Nam H , Guo M , Lee K , Li R , Xing L , Gao H 
Published: July 2014

Purpose:Inspired by compressive sensing, sparsity regularized iterative reconstruction method has been extensively studied. However, its utility pertinent to multislice helical 4D CT for radiotherapy with respect to imaging quality, dose, and time has not been thoroughly addressed. As the beginning of such an investigation, this work carries out the initial comparison of reconstructed imaging quality between sparsity regularized iterative method and analytic method through static phantom studies using a state‐of‐art 128‐channel multi‐slice Siemens helical CT scanner.Methods:In our iterative method, tensor framelet (TF) is chosen as the regularization method for its superior performance from total variation regularization in terms of reduced piecewise‐constant artifacts and improved imaging quality that has been demonstrated in our prior work. On the other hand, X‐ray transforms and its adjoints are computed on‐the‐fly through GPU implementation using our previous developed fast parallel algorithms with O(1) complexity per computing thread. For comparison, both FDK (approximate analytic method) and Katsevich algorithm (exact analytic method) are used for multislice helical CT image reconstruction.Results:The phantom experimental data with different imaging doses were acquired using a state‐of‐art 128‐channel multi‐slice Siemens helical CT scanner. The reconstructed image quality was compared between TF‐based iterative method, FDK and Katsevich algorithm with the quantitative analysis for characterizing signal‐to‐noise ratio, image contrast, and spatial resolution of high‐contrast and low‐contrast objects.Conclusion:The experimental results suggest that our tensor framelet regularized iterative reconstruction algorithm improves the helical CT imaging quality from FDK and Katsevich algorithm for static experimental phantom studies that have been performed.
SU‐E‐I‐98: Dose Comparison for Pulmonary Embolism CT Studies: Single Energy Vs. Dual Energy
Authors: Mahmood U , Erdi Y 
Published: July 2014

Purpose:The purpose of this study was to assess and compare the size specific dose estimate (SSDE), dose length product (DLP) and noise relationship for pulmonary embolism studies evaluated by single source dual energy computed tomography (DECT) against conventional CT (CCT) studies in a busy cancer center and to determine the dose savings provided by DECT.Methods:An IRB‐approved retrospective study was performed to determine the CTDIvol and DLP from a subset of patients scanned with both DECT and CCT over the past five years. We were able to identify 30 breast cancer patients (6 male, 24 female, age range 24 to 81) who had both DECT and CCT studies performed. DECT scans were performed with a GE HD 750 scanner (140/80 kVp, 480 mAs and 40 mm) and CCT scans were performed with a GE Lightspeed 16 slice scanner (120 kVp, 352 mAs, 20 mm). Image noise was measured by placing an ROI and recording the standard deviation of the mean HU along the descending aorta.Results:The average DECT patient size specific dose estimate was to be 14.2 ± 1.7 mGy as compared to 22.4 ± 2.7 mGy from CCT PE studies, which is a 37% reduction in the SSDE. The average DECT DLP was 721.8 ± 84.6 mGy‐cm as compared to 981.8 ± 106.1 mGy‐cm for CCT, which is a 26% decrease. Compared to CCT the image noise was found to decrease by 19% when using DECT for PE studies.Conclusion:DECT SSDE and DLP measurements indicate dose savings and image noise reduction when compared to CCT. In an environment that heavily debates CT patient doses, this study confirms the effectiveness of DECT in PE imaging.
SU‐E‐I‐99: Estimation of Effective Charge Distribution by Dual‐Energy CT Reconstruction
Authors: Sakata D , Kida S , Nakano M , Masutani Y , Nakagawa K , Haga A 
Published: July 2014

Purpose:Computed Tomography (CT) is a method to produce slice image of specific volume from the scanned x‐ray projection images. The contrast of CT image is correlated with the attenuation coefficients of the x‐ray in the object. The attenuation coefficient is strongly dependent on the x‐ray energy and the effective charge of the material. The purpose of this presentation is to show the effective charge distribution predicted by CT images reconstructed with kilovoltage(kV) and megavoltage(MV) x‐ray energy.Methods:The attenuation coefficients of x‐ray can be characterized by cross section of photoionization and Compton scattering for the specific xray energy. In particular, the photoionization cross section is strongly correlated with the effective charge of the object. Hence we can calculate effective charge by solving the coupled equation between the attenuation coefficient and the theoretical cross section. For this study, we use the megavoltage (MV) and kilovoltage (kV) x‐rays of Elekta Synergy as the dual source x‐ray, and CT image of the Phantom Laboratory CatPhan is reconstructed by the filtered back projection (FBP) and iterative algorithm for cone‐beam CT (CBCT).Results:We report attenuation coefficients of each component of the CatPhan specified by each x‐ray source. Also the effective charge distribution is evaluated by the MV and kV dual x‐ray sources. The predicted effective charges are comparable with the nominal ones.Conclusion:We developed the MV and kV dual‐source CBCT reconstruction to yield the effective charge distribution. For more accuracy, it is critical to remove an effect of the scattering photon in the CBCT reconstruction algorithm. The finding will be fine reference of the effective charge of tissue and lead to the more realistic absorbed‐dose calculation.This work was partly supported by the JSPS Core‐to‐Core Program(No. 23003), and this work was partly supported by JSPS KAKENHI 24234567.
SU‐E‐J‐07: A Functional MR Protocol for the Pancreatic Tumor Delineation
Authors: Andreychenko A , Heerkens H , Meijer G , van Vulpen M , Lagendijk J , van den Berg C 
Published: July 2014

Purpose:Pancreatic cancer is one of the cancers with the poorest survival prognosis. At the time of diagnosis most of pancreatic cancers are unresectable and those patients can be treated by radiotherapy. Radiotherapy for pancreatic cancer is limited due to uncertainties in CT‐based delineations. MRI provides an excellent soft tissue contrast. Here, an MR protocol is developed to improve delineations for radiotherapy treatment of pancreatic cancer. In a later stage this protocol can also be used for on‐line visualization of the pancreas during MRI guided treatments.Methods:Nine pancreatic cancer patients were included. The MR protocol included T2 weighted(T2w), T1 weighted(T1w), diffusion weighted(DWI) and dynamic contrast enhanced(DCE) techniques. The tumor was delineated on T2w and T1w MRI by an experienced radiation oncologist. Healthy pancreas or pancreatitis (assigned by the oncologist based on T2w) areas were also delineated. Apparent diffusion coefficient(ADC), and area under the curve(AUC)/time to peak(TTP) maps were obtained from DWI and DCE scans, respectively.Results:A clear demarcation of tumor area was visible on b800 DWI images in 5 patients. ADC maps of those patients characterized tumor as an area with restricted water diffusion. Tumor delineations based on solely DCE were possible in 7 patients. In 6 of those patients AUC maps demonstrated tumor heterogeneity: a hypointense area with a hyperintense ring. TTP values clearly discriminated the tumor and the healthy pancreas but could not distinguish tumor and the pancreatitis accurately.Conclusion:MR imaging results in a more pronounced tumor contrast than contrast enhanced CT. The addition of quantitative, functional MRI provides valuable, additional information to the radiation oncologist on the spatial tumor extent by discriminating tumor from the healthy pancreas(TTP, DWI) and characterizing the tumor(ADC). Our findings indicate that tumor delineation in pancreatic cancer can greatly benefit from the addition of MRI and especially functional MR techniques.
SU‐E‐J‐08: A Hybrid Three Dimensional Registration Framework for Image‐Guided Accurate Radiotherapy System ARTS‐IGRT
Authors: Wu Q , Pei X , Cao R , Hu L , Wu Y 
Published: July 2014

Purpose:The purpose of this work was to develop a registration framework and method based on the software platform of ARTS‐IGRT and implement in C++ based on ITK libraries to register CT images and CBCT images. ARTS‐IGRT was a part of our self‐developed accurate radiation planning system ARTS.Methods:Mutual information (MI) registration treated each voxel equally. Actually, different voxels even having same intensity should be treated differently in the registration procedure. According to their importance values calculated from self‐information, a similarity measure was proposed which combined the spatial importance of a voxel with MI (S‐MI). For lung registration, Firstly, a global alignment method was adopted to minimize the margin error and achieve the alignment of these two images on the whole. The result obtained at the low resolution level was then interpolated to become the initial conditions for the higher resolution computation. Secondly, a new similarity measurement S‐MI was established to quantify how close the two input image volumes were to each other. Finally, Demons model was applied to compute the deformable map.Results:Registration tools were tested for head‐neck and lung images and the average region was 128*128*49. The rigid registration took approximately 2 min and converged 10% faster than traditional MI algorithm, the accuracy reached 1mm for head‐neck images. For lung images, the improved symmetric Demons registration process was completed in an average of 5 min using a 2.4GHz dual core CPU.Conclusion:A registration framework was developed to correct patient's setup according to register the planning CT volume data and the daily reconstructed 3D CBCT data. The experiments showed that the spatial MI algorithm can be adopted for head‐neck images. The improved Demons deformable registration was more suitable to lung images, and rigid alignment should be applied before deformable registration to get more accurate result.Supported by National Natural Science Foundation of China (NO.81101132) and Natural Science Foundation of Anhui Province (NO.11040606Q55)
SU‐E‐J‐13: A New Variable for Plan Quality Evaluation Based On Normal Tissue Sparing
Authors: Zhang Q , Lei Y , Zheng D , Morgan B , Driewer J , Zhang M , Li S , Zhou S , Zhen W , Thompson R , Lin C , Wahl A , Enke C 
Published: July 2014

Purpose:The dose dropping speed (DDS) in normal tissue was proposed to assess plan quality. It was tested in stereotactic radiosurgery (SRS) cases.Methods:The DDS was tested with a total 40 plans for 8 SRS cases. Dynamic conformal arc plans were generated for each case, with prescription dose to isodose levels (IDL) ranging from 50% to 90% with 10% increment to cover the PTV. Forty non‐overlapping rind structures of 1mm thickness were created layer by layer from each PTV surface. The average dose in each rind was calculated and fitted with a double exponential function (DEF) of the distance from the PTV surface, which models the steep and moderate portions of the average dose curve in normal tissue. The parameter charactering the steep portion of the average dose curve in the DEF quantifies the DDS in the normal tissue receiving high dose. Provided that the prescription dose covers the whole PTV, a greater DDS indicates better normal tissue sparing.Results:Among all plans, the DDS was found to be the smallest for prescription of 90% IDL and reached a higher plateau region for prescription to 60% or 70%. The ratio of the highest slope to that of 90% prescription was 1.68±0.35. Analyzed with ANOVA, the DDS difference between the plans with prescription to 60% or 70% IDLS and those with prescription to 90% IDL were found significant (p<0.01). This can be attributed to the field size and penumbra slope change with different prescription levels. The trend became less pronounced with increasing PTV size due to less change of field profile for larger field size.Conclusion:A method was proposed to estimate dose dropping speed as a measure of plan quality. Based on this measure, prescriptions to 60% and 70% IDLs were found to provide best normal tissue sparing.
SU‐E‐J‐17: A Study of Accelerator‐Induced Cerenkov Radiation as a Beam Diagnostic and Dosimetry Tool
Authors: Bateman F , Tosh R 
Published: July 2014

Purpose:To investigate accelerator‐induced Cerenkov radiation imaging as a possible beam diagnostic and medical dosimetry tool.Methods:Cerenkov emission produced by clinical accelerator beams in a water phantom was imaged using a camera system comprised of a high‐sensitivity thermoelectrically‐cooled CCD camera coupled to a large aperture (f/0.75) objective lens with 16:1 magnification. This large format lens allows a significant amount of the available Cerenkov light to be collected and focused onto the CCD camera to form the image. Preliminary images, obtained with 6 MV photon beams, used an unshielded camera mounted horizontally with the beam normal to the water surface, and confirmed the detection of Cerenkov radiation. Several improvements were subsequently made including the addition of radiation shielding around the camera, and altering of the beam and camera angles to give a more favorable geometry for Cerenkov light collection. A detailed study was then undertaken over a range of electron and photon beam energies and dose rates to investigate the possibility of using this technique for beam diagnostics and dosimetry.Results:A series of images were obtained at a fixed dose rate over a range of electron energies from 6 to 20 MeV. The location of maximum intensity was found to vary linearly with the energy of the beam. A linear relationship was also found between the light observed from a fixed point on the central axis and the dose rate for both photon and electron beams.Conclusion:We have found that the analysis of images of beam‐induced Cerenkov light in a water phantom has potential for use as a beam diagnostic and medical dosimetry tool. Our future goals include the calibration of the light output in terms of radiation dose and development of a tomographic system for 3D Cerenkov imaging in water phantoms and other media.
SU‐E‐J‐18: A Thermal Simulation Model and Validation for Percutaneous Cancer Ablation
Authors: Deshazer G , Dupuy D , Merck D 
Published: July 2014

Purpose:Image‐guided percutaneous ablation is an effective, inexpensive, and accessible treatment for liver, lung, and kidney cancers. However, because of its relatively high recurrence rate, percutaneous ablation is usually considered to be palliative only. We hypothesize that the high recurrence rate is due in part to poor margin control resulting from inaccurate treatment models in procedure planning. To address this shortcoming, we are developing a thermal simulation model for percutaneous cancer ablation from first principles.Methods:Our model uses finite element methods to solve Penne's Heat Equation and Maxwell's equations for electromagnetic energy transfer in matter over time. The simulation accounts for applicator geometry and materials as taken from actual clinical devices, and incorporates appropriate density, thermal conductivity properties, dielectric properties, power dissipation, and the relative water content for a homogeneous liver tissue domain.Results:The solution generated is a continuous 3D thermal profile over time. The simulated 60 degree Celsius isotherm at 60 watts for 10 minutes in homogenous liver tissue is accurate to within approximately 5% (i.e., an average 2mm variance from a 36mm expected width) of the vendor specification and within 12% (5mm) of our own ex vivo ablation procedures as measured by 4D CT and visual inspection of the coagulation zone. Simulations at other input settings give similar results within 5%–15% of expected and empirically observed results.Conclusion:This promising initial model forms the basis of ongoing work in principled thermal simulation for ablation planning. Our next goals are to incorporate heterogeneous tissue types and heat sinks in the solution domain and validate the resulting simulation against our ongoing clinical data collection.
SU‐E‐J‐19: Accuracy of Dual‐Energy CT‐Derived Relative Electron Density for Proton Therapy Dose Calculation
Authors: Mullins J , Bues M , Duan X , Kruse J , Herman M 
Published: July 2014

Purpose:To determine the suitability of dual‐energy CT (DECT) to calculate relative electron density (RED) of tissues for accurate proton therapy dose calculation.Methods:DECT images of RED tissue surrogates were acquired at 80 and 140 kVp. Samples (RED=0.19−2.41) were imaged in a water‐equivalent phantom in a variety of configurations. REDs were calculated using the DECT numbers and inputs of the high and low energy spectral weightings. DECT‐derived RED was compared between geometric configurations and for variations in the spectral inputs to assess the sensitivity of RED accuracy versus expected values.Results:RED accuracy was dependent on accurate spectral input influenced by phantom thickness and radius from the phantom center. Material samples located at the center of the phantom generally showed the best agreement to reference RED values, but only when attenuation of the surrounding phantom thickness was accounted for in the calculation spectra. Calculated RED changed by up to 10% for some materials when the sample was located at an 11 cm radius from the phantom center. Calculated REDs under the best conditions still differed from reference values by up to 5% in bone and 14% in lung.Conclusion:DECT has previously been used to differentiate tissue types based on RED and Z for binary tissue‐type segmentation. To improve upon the current standard of empirical conversion of CT number to RED for treatment planning dose calculation, DECT methods must be able to calculate RED to better than 3% accuracy throughout the image. The DECT method is sensitive to the accuracy of spectral inputs used for calculation, as well as to spatial position in the anatomy. Effort to address adjustments to the spectral calculation inputs based on position and phantom attenuation will be required before DECT‐determined RED can achieve a consistent level of accuracy for application in dose calculation.
SU‐E‐J‐22: Alternative Method for Evaluating the Need for Replanning in Patient's with Significant Anatomical Changes
Authors: Myers P , Tran D , Liu T , Rodriguez‐Rivera E 
Published: July 2014

Purpose:The use of IGRT is highlighting the issue of anatomical patient changes during treatment due to weight loss and/or tumor shrinkage. A means of quickly reviewing the need to replan is important to maximize efficiency and review the necessity of modifying treatment planning. The goal of this project is to use an alternative method of evaluation for replanning that does not involve extra patient scanning or specific deformable registration software.Methods:Five patients that had undergone daily CBCT imaging during treatment and were noted to have considerable changes in anatomy due to weight loss or tumor shrinkage were evaluated with two methods. First, CBCT external volumes were subtracted from original planning CT to obtain a “change‐in‐volume” contour. The density of this contour was overridden to that of air and original plan recalculated. Second, the original plan was recalculated on a new CT scan taken the same day as the CBCT for comparison. The contours remained unchanged from the original planning scan.Results:So far 1 patient has been evaluated using both methods. The DVH comparison shows similar results between each method for the target tissues (CTV and PTV) as well as critical structures (right parotid and spinal cord). Using the CBCT method mean doses for each structure examined were within 3.2% of those calculated with a new CT scan. The remaining four patients will be evaluated similarly after a new CT scan is obtained.Conclusion:By using the patient's daily CBCT scan from setup prior to treatment, a quick method for evaluating anatomical changes and the need to replan a patient during the course of treatment was demonstrated. This method prevents the need to rescan the patient initially and allows a quick visualization of possible dose differences caused by a significant change in body habitus.