bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐A‐18C‐08: Design of a Small Animal Contrast Enhanced Dual Energy CT
Authors: Martin R , Li B , Pan T 
Published: July 2014

Purpose:Dual energy CT has a variety of uses in a small animal setting including quantification and enhanced visualization of contrast agent. This study aims to determine the best energy combinations for contrast enhanced DECT on the XRAD 225Cx (Precision x‐ray), a small animal IGRT system with a nominal energy range of 20 – 225 kVp. Focus was placed on material density accuracy and low contrast detectability.Methods:Simulations of single energy scans of an object containing concentrations of iodine varying from 0.5 to 50 mg/ml were performed using the simulation package ImaSim. Energy spectra from 50 – 220 kVp were calculated using the same software. For approximate Poisson noise modeling, mAs were chosen such that 30% of the total 10cGy dose was assigned to the low energy scan. A calibration involving projections of objects containing different thicknesses of iodine (0–0.5 mm) and water (0–50 mm) was performed for each energy and fit to a cubic equation as the calibration curve for each energy pair.Results:Contrast to noise ratios of the iodine material images and accuracies in iodine density measurements were measured. Gradual improvements in each metric were seen with increasing high energy. Larger improvements in CNR were observed for decreasing the low energy. Errors in iodine density were generally close to 5% for concentrations of iodine above 3 mg/ml but increased to around 15% for 50 kVp, likely due to its proximity to the discontinuity caused by the k‐edge of iodine.Conclusion:Based on these simulations, the best energy combination for detecting low concentrations of iodine using a projection space calibration procedure is 50/200 kVp. However, if accuracy is most important 80/220 kVp is ideal, with 60/220 kVp being a good compromise to achieve both goals. Future work is necessary to verify these conclusions with physical data.
TH‐A‐9A‐01: Active Optical Flow Model: Predicting Voxel‐Level Dose Prediction in Spine SBRT
Authors: Liu J , Wu Q.J. , Yin F , Kirkpatrick J , Cabrera A , Ge Y 
Published: July 2014

Purpose:To predict voxel‐level dose distribution and enable effective evaluation of cord dose sparing in spine SBRT.Methods:We present an active optical flow model (AOFM) to statistically describe cord dose variations and train a predictive model to represent correlations between AOFM and PTV contours. Thirty clinically accepted spine SBRT plans are evenly divided into training and testing datasets. The development of predictive model consists of 1) collecting a sequence of dose maps including PTV and OAR (spinal cord) as well as a set of associated PTV contours adjacent to OAR from the training dataset, 2) classifying data into five groups based on PTV's locations relative to OAR, two “Top”s, “Left”, “Right”, and “Bottom”, 3) randomly selecting a dose map as the reference in each group and applying rigid registration and optical flow deformation to match all other maps to the reference, 4) building AOFM by importing optical flow vectors and dose values into the principal component analysis (PCA), 5) applying another PCA to features of PTV and OAR contours to generate an active shape model (ASM), and 6) computing a linear regression model of correlations between AOFM and ASM.When predicting dose distribution of a new case in the testing dataset, the PTV is first assigned to a group based on its contour characteristics. Contour features are then transformed into ASM's principal coordinates of the selected group. Finally, voxel‐level dose distribution is determined by mapping from the ASM space to the AOFM space using the predictive model.Results:The DVHs predicted by the AOFM‐based model and those in clinical plans are comparable in training and testing datasets. At 2% volume the dose difference between predicted and clinical plans is 4.2±4.4% and 3.3±3.5% in the training and testing datasets, respectively.Conclusion:The AOFM is effective in predicting voxel‐level dose distribution for spine SBRT.Partially supported by NIH/NCI under grant #R21CA161389 and a master research grant by Varian Medical System.
TH‐A‐9A‐03: Dosimetric Effect of Rotational Errors for Lung Stereotactic Body Radiotherapy
Authors: Lee J , Park J , Kim J , Kim H , Kim H , Ye S 
Published: July 2014

Purpose:To evaluate the dosimetric effects on target volume and organs at risk (OARs) due to roll rotational errors in treatment setup of stereotactic body radiation therapy (SBRT) for lung cancer.Methods:There were a total of 23 volumetric modulated arc therapy (VMAT) plans for lung SBRT examined in this retrospective study. Each CT image of VMAT plans was intentionally rotated by ±1°, ±2°, and ±3° to simulate roll rotational setup errors. The axis of rotation was set at the center of T‐spine. The target volume and OARs in the rotated CT images were re‐defined by deformable registration of original contours. The dose distributions on each set of rotated images were re‐calculated to cover the planning target volume (PTV) with the prescription dose before and after the couch translational correction. The dose‐volumetric changes of PTVs and spinal cords were analyzed.Results:The differences in D95% of PTVs by −3°, −2°, −1°, 1°, 2°, and 3° roll rotations before the couch translational correction were on average −11.3±11.4%, −5.46±7.24%, −1.11±1.38% −3.34±3.97%, −9.64±10.3%, and −16.3±14.7%, respectively. After the couch translational correction, those values were −0.195±0.544%, −0.159±0.391%, −0.188±0.262%, −0.310±0.270%, −0.407±0.331%, and −0.433±0.401%, respectively. The maximum dose difference of spinal cord among the 23 plans even after the couch translational correction was 25.9% at −3° rotation.Conclusions:Roll rotational setup errors in lung SBRT significantly influenced the coverage of target volume using VMAT technique. This could be in part compensated by the translational couch correction. However, in spite of the translational correction, the delivered doses to the spinal cord could be more than the calculated doses. Therefore if rotational setup errors exist during lung SBRT using VMAT technique, the rotational correction would rather be considered to prevent over‐irradiation of normal tissues than the translational correction.
TH‐C‐12A‐11: Target Correlation of a 3D Surface Surrogate for Left Breast Irradiation Using the Respiratory‐Gated Deep‐Inspiration Breath‐Hold Technique
Authors: Rong Y , Walston S 
Published: July 2014

Purpose:To evaluate the use of 3D optical surface imaging as a new surrogate for respiratory motion gated deep‐inspiration breath‐hold (DIBH) technique for left breast cancer patients.Methods:Patients with left‐sided breast cancer after lumpectomy or mastectomy were selected as candidates for DIBH technique for their external beam radiation therapy. Treatment plans were created on both free breathing (FB) and DIBH CTs to determine whether DIBH was beneficial in reducing heart doses. The Real‐time Position Management (RPM) system was used to acquire patient's breathing trace during DIBH CT acquisition and treatment delivery. The reference 3D surface models from FB and DIBH CTs were generated and transferred to the “AlignRT” system for patient positioning and real‐time treatment monitoring. MV Cine images were acquired for each beam as quality assurance for intra‐fractional position verification. The chest wall excursions measured on these images were used to define the actual target position during treatment, and to investigate the accuracy and reproducibility of RPM and AlignRT.Results:Reduction in heart dose can be achieved for left‐sided breast patients using DIBH. Results showed that RPM has poor correlation with target position, as determined by the MV Cine imaging. This indicates that RPM may not be an adequate surrogate in defining the breath‐hold level when used alone. Alternatively, the AlignRT surface imaging demonstrated a better correlation with the actual CW excursion during DIBH. Both the vertical and magnitude real‐time deltas (RTDs) reported by AlignRT can be used as the gating parameter, with a recommend threshold of ±3 mm and 5 mm, respectively.Conclusion:3D optical surface imaging serves as a superior target surrogate for the left breast treatment when compared to RPM. Working together with the realtime MV Cine imaging, they ensure accurate patient setup and dose delivery, while minimizing the imaging dose to patients.
TH‐E‐BRE‐01: A 3D Solver of Linear Boltzmann Transport Equation Based On a New Angular Discretization Method with Positivity for Photon Dose Calculation Benchmarked with Geant4
Authors: Hong X , Gao H 
Published: July 2014

Purpose:The Linear Boltzmann Transport Equation (LBTE) solved through statistical Monte Carlo (MC) method provides the accurate dose calculation in radiotherapy. This work is to investigate the alternative way for accurately solving LBTE using deterministic numerical method due to its possible advantage in computational speed from MC.Methods:Instead of using traditional spherical harmonics to approximate angular scattering kernel, our deterministic numerical method directly computes angular scattering weights, based on a new angular discretization method that utilizes linear finite element method on the local triangulation of unit angular sphere. As a Result, our angular discretization method has the unique advantage in positivity, i.e., to maintain all scattering weights nonnegative all the time, which is physically correct. Moreover, our method is local in angular space, and therefore handles the anisotropic scattering well, such as the forward‐peaking scattering. To be compatible with image‐guided radiotherapy, the spatial variables are discretized on the structured grid with the standard diamond scheme. After discretization, the improved sourceiteration method is utilized for solving the linear system without saving the linear system to memory. The accuracy of our 3D solver is validated using analytic solutions and benchmarked with Geant4, a popular MC solver.Results:The differences between Geant4 solutions and our solutions were less than 1.5% for various testing cases that mimic the practical cases. More details are available in the supporting document.Conclusion:We have developed a 3D LBTE solver based on a new angular discretization method that guarantees the positivity of scattering weights for physical correctness, and it has been benchmarked with Geant4 for photon dose calculation.
TH‐E‐BRE‐08: GPU‐Monte Carlo Based Fast IMRT Plan Optimization
Authors: Li Y , Tian Z , Shi F , Jiang S , Jia X 
Published: July 2014

Purpose:Intensity‐modulated radiation treatment (IMRT) plan optimization needs pre‐calculated beamlet dose distribution. Pencil‐beam or superposition/convolution type algorithms are typically used because of high computation speed. However, inaccurate beamlet dose distributions, particularly in cases with high levels of inhomogeneity, may mislead optimization, hindering the resulting plan quality. It is desire to use Monte Carlo (MC) methods for beamlet dose calculations. Yet, the long computational time from repeated dose calculations for a number of beamlets prevents this application. It is our objective to integrate a GPU‐based MC dose engine in lung IMRT optimization using a novel two‐steps workflow.Methods:A GPU‐based MC code gDPM is used. Each particle is tagged with an index of a beamlet where the source particle is from. Deposit dose are stored separately for beamlets based on the index. Due to limited GPU memory size, a pyramid space is allocated for each beamlet, and dose outside the space is neglected. A two‐steps optimization workflow is proposed for fast MC‐based optimization. At first step, rough beamlet dose calculations is conducted with only a small number of particles per beamlet. Plan optimization is followed to get an approximated fluence map. In the second step, more accurate beamlet doses are calculated, where sampled number of particles for a beamlet is proportional to the intensity determined previously. A second‐round optimization is conducted, yielding the final Result.Results:For a lung case with 5317 beamlets, 105 particles per beamlet in the first round, and 108 particles per beam in the second round are enough to get a good plan quality. The total simulation time is 96.4 sec.Conclusion:A fast GPU‐based MC dose calculation method along with a novel two‐step optimization workflow are developed. The high efficiency allows the use of MC for IMRT optimizations.
TH‐E‐BRE‐11: Adaptive‐Beamlet Based Finite Size Pencil Beam (AB‐FSPB) Dose Calculation Algorithm for Independent Verification of IMRT and VMAT
Authors: Park C , Arhjoul L , Yan G , Lu B , Li J , Liu C 
Published: July 2014

Purpose:In current IMRT and VMAT settings, the use of sophisticated dose calculation procedure is inevitable in order to account complex treatment field created by MLCs. As a consequence, independent volumetric dose verification procedure is time consuming which affect the efficiency of clinical workflow. In this study, the authors present an efficient Pencil Beam based dose calculation algorithm that minimizes the computational procedure while preserving the accuracy.Methods:The computational time of Finite Size Pencil Beam (FSPB) algorithm is proportional to the number of infinitesimal identical beamlets that constitute the arbitrary field shape. In AB‐FSPB, the dose distribution from each beamlet is mathematically modelled such that the sizes of beamlets to represent arbitrary field shape are no longer needed to be infinitesimal nor identical. In consequence, it is possible to represent arbitrary field shape with combinations of different sized and minimal number of beamlets.Results:On comparing FSPB with AB‐FSPB, the complexity of the algorithm has been reduced significantly. For 25 by 25 cm2 squared shaped field, 1 beamlet of 25 by 25 cm2 was sufficient to calculate dose in AB‐FSPB, whereas in conventional FSPB, minimum 2500 beamlets of 0.5 by 0.5 cm2 size were needed to calculate dose that was comparable to the Result computed from Treatment Planning System (TPS). The algorithm was also found to be GPU compatible to maximize its computational speed. On calculating 3D dose of IMRT (∼30 control points) and VMAT plan (∼90 control points) with grid size 2.0 mm (200 by 200 by 200), the dose could be computed within 3∼5 and 10∼15 seconds.Conclusion:Authors have developed an efficient Pencil Beam type dose calculation algorithm called AB‐FSPB. The fast computation nature along with GPU compatibility has shown performance better than conventional FSPB. This completely enables the implantation of AB‐FSPB in the clinical environment for independent volumetric dose verification.
TH‐E‐BRF‐06: Kinetic Modeling of Tumor Response to Fractionated Radiotherapy
Authors: Zhong H , Gordon J , Chetty I 
Published: July 2014

Purpose:Accurate calibration of radiobiological parameters is crucial to predicting radiation treatment response. Modeling differences may have a significant impact on calibrated parameters. In this study, we have integrated two existing models with kinetic differential equations to formulate a new tumor regression model for calibrating radiobiological parameters for individual patients.Methods:A system of differential equations that characterizes the birth‐and‐death process of tumor cells in radiation treatment was analytically solved. The solution of this system was used to construct an iterative model (Z‐model). The model consists of three parameters: tumor doubling time Td, half‐life of dying cells Tr and cell survival fraction SFD under dose D. The Jacobian determinant of this model was proposed as a constraint to optimize the three parameters for six head and neck cancer patients. The derived parameters were compared with those generated from the two existing models, Chvetsov model (C‐model) and Lim model (L‐model). The C‐model and L‐model were optimized with the parameter Td fixed.Results:With the Jacobian‐constrained Z‐model, the mean of the optimized cell survival fractions is 0.43±0.08, and the half‐life of dying cells averaged over the six patients is 17.5±3.2 days. The parameters Tr and SFD optimized with the Z‐model differ by 1.2% and 20.3% from those optimized with the Td‐fixed C‐model, and by 32.1% and 112.3% from those optimized with the Td‐fixed L‐model, respectively.Conclusion:The Z‐model was analytically constructed from the cellpopulation differential equations to describe changes in the number of different tumor cells during the course of fractionated radiation treatment. The Jacobian constraints were proposed to optimize the three radiobiological parameters. The developed modeling and optimization methods may help develop high‐quality treatment regimens for individual patients.
SU‐C‐16A‐06: Optimum Radiation Source for Radiation Therapy of Skin Cancer
Authors: Safigholi Habib , Meigooni A S. 
Published: July 2014

Purpose:Recently, different applicators are designed for treatment of the skin cancer such as scalp and legs, using Ir‐192 HDR Brachytherapy Sources (IR‐HDRS), Miniature Electronic Brachytherapy Sources (MEBXS), and External Electron Beam Radiation Therapy (EEBRT). Although, all of these methodologies may deliver the desired radiation dose to the skin, the dose to the underlying bone may become the limiting factor for selection of the optimum treatment technique. In this project the radiation dose delivered to the underlying bone has been evaluated as a function of the radiation source and thickness of the underlying bone.Methods:MC simulations were performed using MCNP5 code. In these simulations, the mono‐energetic and non‐divergent photon beams of 30 keV, 50 keV, and 70 keV for MEBXS, 380 keV photons for IR‐HDRS, and 6 MeV mono‐energetic electron beam for EEBRT were modeled. A 0.5 cm thick soft tissue (0.3 cm skin and 0.2 cm adipose) with underlying 0.5 cm cortical bone followed by 14 cm soft tissue are utilized for simulations.Results:Dose values to bone tissue as a function of beam energy and beam type, for a delivery of 5000 cGy dose to skin, were compared. These results indicate that for delivery of 5000 cGy dose to the skin surface with 30 keV, 50 keV, 70 keV of MEBXS, IR‐HDRS, and EEBRT techniques, bone will receive 31750 cGy, 27450 cGy, 18550 cGy, 4875 cGy, and 10450 cGy, respectively.Conclusion:The results of these investigations indicate that, for delivery of the same skin dose, average doses received by the underlying bone are 5.2 and 2.2 times larger with a 50 keV MEBXS and EEBRT techniques than IR‐HDRS, respectively.
SU‐C‐16A‐07: Sculpting Isodose Lines: Design of An Internally Shielded Tandem for Cervical Cancer Brachytherapy
Authors: Zhang M , Mo X , Yue N , Zou J 
Published: July 2014

Purpose:With the prescription method moving from point A to 3D volume based in cervical cancer HDR brachytherapy, the traditional pear‐shaped isodose lines are desired to be sculptured to conform to the irregular shaped target. The standard single channel tandem cannot generate asymmetric isodose lines. Most of the directionally shielded sources proposed in literature are challenging to manufacture and operate. In this study, we proposed a novel internally shielded tandem applicator design which gave users more freedom to manipulate isodose lines while planning.Methods:The proposed tandem design has one centrally located lead cylindrical rod of 8 mm in diameter serving as the internal shield. Multiple source channels with the diameter of 2 mm are evenly spaced and engraved on the central cylindrical rod. The overall diameter of the tandem with polymer encapsulation was kept to be 10 mm. Various number of channels and engraving depths have been tested in the design process. Geant4 Monte Carlo toolkit was used for dose calculation assuming a Varian VS2000 source was placed inside the applicator. A Monte Carlo based planning system has been developed in‐house to generate brachytherapy plans. Test plans by using this internally shielded tandem were generated for 3 clinical cases.Results:Water phantom results shown the dose distribution from a VS2000 source in the tandem was strongly distorted towards one direction due to the presence of shielding material. Conformal plans with asymmetric isodose distributions around the tandem can be generated by optimizing dwell times in different channels.Conclusion:An effective and easy‐to‐use internally shielded tandem was developed. It gave user the freedom to sculpt isodose lines to generate conformal plans for cervical cancer brachytherapy.
SU‐C‐19A‐05: Treatment Chairs for Modern Radiation Therapy Treatments
Authors: Court L , Fullen D , Tharp K , Palmer J , Ungchusri G , Reyes L , Tong T , Nguyen S , Phillips T , Balter P 
Published: July 2014

Purpose:Treating patients in a seated position has potential advantages including improved comfort, increased lung volume, and reduced respiratory motion. We compared chair designs for head and neck, thoracic and breast patients for use with either IGRT linacs or a proposed low‐cost fixed horizontal beam‐line machine.Methods:Three treatment chairs were designed and constructed. Two of the chairs are based on a massage‐chair, with the patient angled slightly forwards and knee rests used to minimize intra‐fraction slouch. The third chair design is more conventional; the patient is angled backwards, with indexed positioning devices and the ability to attach thermoplastic masks. Patient geometries, including PTV location and patient sizes, were extracted from 137 CTs of past patients were used to model the probability of collision between the patient and the linac for various seated positions. All chairs were designed around the weight limits for couches on our linacs. At the time of writing we have just received IRB approval for imaging studies to evaluate comfort, and intra‐ and interfraction reproducibility.Results:The geometric analysis showed that head and neck patients and thoracic patients could be treated without collision. However, there is very limited space between the patient and the treatment/imaging devices, so careful design of the chair is essential. The position of the treatment target and extended arm positioning means that this is a particular concern for thoracic and breast patients. This was demonstrated for one of the prototype chairs designed for breast treatment where the arm holders would collide with the kV detector. The extra clearance of a dedicated fixed‐beam linac would overcome these difficulties. Intra‐ and inter‐fraction reproducibility results will be presented at the meeting.Conclusion:To take advantage of the clinical advantages of seated treatments, appropriate treatment chairs are needed. A dedicate fixed‐beam linac may enable more options.This work was partially funded by Varian Medical Systems