bluuebunny/crossref_metadata_2025_split huggingface dataset:
TH‐EF‐BRD‐01: Fluence Map Optimization Using a Voxel‐Based Reduced‐Order Constrained Optimization Model
Authors: Nourzadeh H , Radke R , Jackson A 
Published: June 2015

Purpose:To develop a method for adaptively imposing dose constraints on individual voxels and structures in IMRT planning, such that a sequence of computationally tractable, low‐dimensional constrained optimization problems is solved that leads to plans satisfying dose‐volume and other clinical constraints.Methods:The previously proposed Reduced Order Constrained Optimization (ROCO) algorithm is applied to parameterize an IMRT problem by a small number of coefficients on learned principal components, instead of a large number of independent beamlet fluences. A sequence of constrained optimization problems is solved over the set of coefficients in which the importance of each voxel and structure is adaptively changed in the objective function. Instead of manually investigating good settings for these parameters, an adaptive gain scheduling rule based on control theory automatically adjusts the weights, quickly converging to a plan satisfying the clinical constraints. In particular, we apply a decentralized proportional‐integral controller that adjusts structure weights using dose‐volume constraint (DVC) violation feedback. We compare our method against a previous approach in which subsets of voxels were iteratively selected and hard‐constrained in an attempt to satisfy DVCs.Results:The technique was tested on five different non‐nodal prostate cases, each resulting in clinically acceptable plans in less than 2.5 minutes on average. The quality of plans is far superior to the alternate method, significantly reducing OARs doses while meeting PTV V95 goals.Conclusion:Compared to alternative optimization schemes in the full intensity space, the propose scheme offers fast convergence rate, demands significantly less memory resources and computational effort, which allows larger IMRT problems to be addressed.
TH‐EF‐BRD‐04: A Fast 4D IMRT/VMAT Planning Method Based On Segment Aperture Morphing
Authors: Klawikowski S , Tai A , Ates O , Ahunbay E , Li X 
Published: June 2015

Purpose:To investigate dosimetric advantages of a 4D IMRT/VMAT planning method employing a segment aperture morphing (SAM) algorithm accounting for respiration‐induced target motion and deformation. The minimal required number of calculated SAM phases was tested to minimize plan creation time.Methods:The new technique involves generating 4D step‐and‐shoot IMRT or VMAT plans based on 10‐phase 4DCT in the following steps: (1) optimizing a flattening‐filter‐free IMRT/VMAT plan based on the 50% phase CT dataset (2) warping contours from the 50%‐phase CT to the remaining phases via deformable image registration (DIR) and manual editing (3) morphing segment apertures of the 50%‐phase plan to each phase CT using SAM that adjusts each aperture shape based on the change of the beam's‐eye‐view of the target contour between the two phases (4) calculating the dose distribution for each phase with the morphed apertures and same MUs as in the 50%‐phase plan, and (5) generating the 4D plan by accumulating the dose from all nine SAM‐corrected phases and the original 50% optimized phase using DIR. 4D plans based on 10, 7, 5 and 3 SAM‐corrected phases were generated for representative lung and pancreatic cancer cases, and were compared using DVH analysis against the gold‐standard 4D plan where all 10 phases are individually planned and optimized. A SAM‐corrected 4D plan was also compared to a simpler phase‐by‐phase isocenter‐shifted plan to assess accounting for tumor deformation and translation opposed to only tumor translation.Results:Plan DVH quality for the 10‐phase and 7‐phase 4D SAM plans were comparable with the fully‐optimized 4D plans (PTV‐D95's within 3% of fully‐optimized plans). SAM based algorithms out‐performed simpler isocenter‐shifted‐only approaches (∼1.5% PTV‐D95 improvement). SAM‐based 4D planning greatly reduces planning time verses individually optimized phase planning techniques.Conclusion:SAM with DIR provides a fast and accurate way to create 4D IMRT/VMAT plans.
TH‐EF‐BRD‐05: A New Intensity Modulation Radiation Therapy (IMRT) Optimizer Solution with Robust Fluence Maps for MLC Segmentation
Authors: Nguyen D , O'Connor D , Yu V , Ruan D , Cao M , Low D , Sheng K 
Published: June 2015

Purpose:Converting theoretical fluence maps to deliverable MLC segments while maintaining plan quality has posed a significant challenge for highly complex IMRT plans involving many fields. Rather than simplifying individual fluence maps, we have formulated the problem as a global dose domain fluence map optimization with anisotropic total variation regularization (FMOATVR) problem and then solve the large scale optimization problem.Methods:The 4π planning platform was used to select and optimize 20 non‐coplanar beams for 2 GBM, 2 head & neck, and 2 lung patients with varying prescription doses, including H&N case #2 that had 3 prescription dose levels of 54 Gy, 59.4 Gy, and 69.96 Gy. The plans were re‐run using FMOATVR and the same 20 4π beams. The L2 norm of dose deviation from the ideal prescription with zero dose to OARs was used as the objective function, which was subjected to anisotropic total variation regularization to encourage piecewise smoothness in the fluence maps. The fluences were stratified into equal step sizes to create 300 MLC segments. The dose distributions were normalized so the prescription dose covered cover 95% of the PTV. H&N case #2 was normalized to cover the 59.4 Gy PTV, which was included in the statistics.Results:Compared to the directly stratified 4π plans (4π DS), the 4π FMOATVR method reduced the average mean and max dose to the OARs by 3.54% and 4.15%, respectively, of the prescription dose. Dose coverage was also improved, evidenced by an average D98 and D99 increase of 1.63% and 2.74% of the prescription dose, respectively. The average PTV homogeneity was increased from 0.833 to 0.905.Conclusion:The global dose domain fluence map optimization formula and its solver provides a straightforward yet potent method to attain high quality while remaining robust to MLC segmentation for complex IMRT.This work is supported in part by Varian Medical Systems, Inc.
TH‐EF‐BRD‐06: Rapid Direct Aperture Optimization Via Piecewise Linear Dose Calculation Based On the Dose Influence Matrix
Authors: Zeng X , Guo M , Gao H 
Published: June 2015

Purpose:Direct aperture optimization (DAO) considers the direct optimization of aperture leaf positions and weights, instead of a two‐step procedure for intensity modulated radiation therapy (IMRT), i.e. first fluence map optimization and then leaf sequencing algorithm. However, the use of the Monte Carlo (MC) method in DAO is often time‐consuming. This work aims to develop a rapid DAO algorithm.Methods:The proposed method is based on the dose influence matrix. That is the leaf position variable is a piecewise linear function of the dose influence matrix. Specifically, the piecewise linear dose calculation model with respect to left and right leaf positions of a aperture consists of three terms: (i) the total dose contribution from the bixels that are fully between the left and right leaf positions; (ii) the partial dose contribution from the leftmost bixel that the left leaf falls into; (iii) the partial dose contribution from the rightmost bixel that the right leaf falls into. As a Result, this model is piecewise linear with respect to the leaf positions.Then instead of MC, this piecewise linear dose calculation engine based on the dose influence matrix is incorporated into the simulated annealing algorithm for DAO. As a Result of rapid dose calculation based on the dose influence matrix, the speed of DAO is improved significantly.Results:The proposed algorithm was tested on the TG119 phantom from the MGH public dataset.Conclusion:Rapid DAO algorithm is developed with the dose calculation engine that replaces MC by the piecewise linear dose calculation based on the dose influence matrix.The authors were partially supported by the NSFC (#11405105), the 973 Program (#2015CB856000) and the Shanghai Pujiang Talent Program (#14PJ1404500).
TH‐EF‐BRD‐10: Spatiotemporal Dose Shaping to Achieve Uniform Fractionation in Healthy Tissues Along with Hypo‐Fractionation in Targets
Authors: Unkelbach J , Bussiere M , Shih H , Chapman P , Loeffler J 
Published: June 2015

Purpose:Fractionation decisions in radiotherapy face the tradeoff between increasing the number of fractions to spare normal tissues, and increasing the total dose to achieve the same effect in the target volume. In that regard, the ideal treatment would fractionate in normal tissues while simultaneously hypo‐fractionating in the target. Interestingly, this is possible to a limited degree by delivering distinct dose distributions in different fractions. The dose distributions have to be designed such that similar doses are delivered to normal tissues while delivering high single fraction doses to parts of the target. We demonstrate that this concept may lead to an improved therapeutic ratio for rotation therapy treatments using conventional photon beams.Methods:Fractionation effects are modeled via the biologically equivalent dose (BED) model. Treatment plan optimization is performed using objective functions evaluated for the cumulative BED delivered at the end of treatment. This allows for simultaneously optimizing multiple distinct treatment plans for different fractions.Results:The concept is demonstrated for large cerebral arteriovenous malformations (AVM) treated in two fractions. It is shown that the optimal treatment delivers a large dose to the center of the AVM in the first fraction. The second fraction delivers the missing dose to the rim of the target volume. The target is divided into center and rim in such a way that the dose received by normal brain adjacent to the AVM is approximately equal in both fractions.Conclusion:The BED in the target can be increased by hypo‐fractionating the central core. Since the fractionation effect is exploited in the normal tissue, this leads to an improved therapeutic ratio overall. The approach may potentially be beneficial for large AVMs or tumors embedded in a dose‐limiting normal tissue treated with stereotactic regimens.
TH‐EF‐BRB‐03: Enhancement of Image Contrast Along the Beam's‐Eye‐View (BEV) Direction Through Development of Imagers Based On Segmented Scintillators and Photon‐Counting Arrays
Authors: Antonuk L , El‐Mohri Y , Zhao Q , Liang A , Koniczek M 
Published: June 2015

Purpose:The contrast provided by conventional portal imagers is constrained by inefficient conversion of the incident radiation, and by the small diagnostic x‐ray component of the treatment beam. Toward improved visualization of the tumor region prior to treatment, as well as improved tumor tracking during treatment, progress is reported on the design of a pair of novel detectors that would address these constraints.Methods:A dual‐energy imager based on a segmented scintillator is being designed using a hybrid model to simulate radiation and optical transport. The simulations, which model operation with a megavoltage treatment beam and with a BEV imaging beam with a significant diagnostic component, employ parameters extracted from a previously developed prototype. Separately, the conceptual design of a second imager incorporating a 2D array of photon counting pixels is being explored through extrapolation of the design of the first prototype photon counting arrays fabricated using thin‐film processing, a process scalable to very large area detectors.Results:The simulations identified a segmented scintillator imager design that, when operated with a BEV imaging beam, provides spatial resolution and contrast comparable to that of gantry‐mounted kV imagers. When operated with a treatment beam, the design provides significantly improved DQE and contrast compared to conventional portal imagers. Extrapolation of initial photon counting array designs indicates that the circuitry necessary to provide energy‐windowing of the diagnostic portion of a therapy beam can be achieved at the pixel pitch associated with current treatment room imagers.Conclusion:These early studies demonstrate potential for improved contrast in projection and volumetric images obtained with the megavoltage beam prior to treatment, while also providing good performance when used with BEV imaging beams. In addition, these studies also support the possibility of improved capability for tumor tracking with such dual‐energy imagers as well as by photon counting array imagers.NIH grant R01‐EB000558
TH‐EF‐BRB‐08: An Efficient and Continuous Surface Reconstruction Method On Point Cloud Captured by a 3D Surface Imaging System
Authors: Liu W , Cheung Y , Sawant A , Ruan D 
Published: June 2015

Purpose:Surface photogrammetry‐based systems (e.g., VisionRT, C‐Rad) are gaining increasing acceptance for patient localization and motion monitoring in radiotherapy. The purpose of this work is to accurately and efficiently reconstruct a continuous surface from noisy point clouds captured by a VisionRT system with high‐speed‐image‐capture capability. In contrast to the conventional approach of explicit/discrete meshing‐type scheme that is often error‐prone, our method yields a continuous representation of the underlying patient surface, which is particularly advantageous for subsequent surface registration and motion tracking.Methods:We developed a level‐set based surface reconstruction method by optimizing a regularized fitting energy from the noisy point cloud from VisionRT. This approach offers additional robustness to noise and missing measurements caused by view occlusion. We applied an efficient narrowband evolving scheme and significantly reduced the time‐complexity by one order of magnitude. Validation was performed on surface data from a lung cancer patient during CT‐simulation by comparing the local geometry of our reconstructed surface against that of the skin surface from CT, within comparable ROIs in the chest area based on mean curvature distributions.Results:Our method successfully reconstructed a continuous and smooth surface, with the missing region reasonably filled. We obtained two similar mean curvature distributions from both reconstructed surface and CT surface, with empirical mean and standard deviation of (µ = −2.7E‐3mm−1, σ = 7.0E‐3mm−1) and (µ = −2.5E‐3mm−1, σ = 5.3E‐3 mm−1), respectively. The similarity of those two distributions demonstrated the ability of our method in preserving local geometry of the reconstructed surface.Conclusion:We have proposed an efficient and accurate surface reconstruction method on point cloud from VisionRT. The proposed method has generated a continuous representation of the underlying patient surface with good robustness against noise and missing measurement. It serves as an important first step for further development of motion tracking methods during radiotherapy.NIH 5R01CA169102‐02
TH‐EF‐BRA‐01: Patient‐Size Specific Analysis of CT Doses From Lung Cancer Screening
Authors: Fujii K , McMillan K , Bostani M , Cagnon C , McNitt‐Gray M 
Published: June 2015

Purpose:The US Centers for Medicare & Medicaid Services (CMS) recently issued its final decision to approve the use of low dose CT for lung cancer screening and described some dose index requirements. The aim of this study is to evaluate CT dose indices from lung cancer screening taking into account patient size.Methods:CT dose index data (CTDIvol, DLP) and patient size (height and weight) to calculate body mass index (BMI) were collected for lung cancer screening exams from Jan 1st to Dec 31th, 2014. All exams used Tube Current Modulation with identical Image Quality Reference parameter (Quality Reference mAs). X‐ray dose management software was used to mine the data. CTDIvol and DLP values were analyzed based on patient's BMI classification. For a subset of patients, the average water equivalent diameter was estimated as well as Size Specific Dose Estimate (SSDE). All results were compared to the Medicare requirements (CTDIvol ≤ 3.0 mGy for a standard sized patient; appropriate reductions for smaller patients and increases for larger patients).Results:The dose indices over 351 patients were (mean ± SD): CTDIvol of 2.1 ± 0.7 mGy (min‐max: 1.2 – 6.0 mGy); DLP of 75 ± 24 mGy*cm (min‐max: 38 – 202 mGy*cm). The CTDIvol values by patient size (BMI) were 1.4 ± 0.2 mGy for underweight (BMI<18.5), 1.7 ± 0.3 mGy for normal weight (BMI of 18.5–24.9), 2.2 ± 0.4 mGy for overweight (BMI of 25.0– 29.9), and 2.9 ± 0.8 mGy for obese (BMI≥30.0). Approximately 9% of total patients had CTDIvol > 3.0 mGy; for each of these cases, the BMI was at least 27.0.Conclusion:The scan protocol used resulted in CTDIvol values well within the Medicare requirements. Patients with larger BMI receive higher CTDIvol, but values > 3.0 mGy only occurred for overweight and obese patients.
TH‐EF‐BRA‐05: Investigation of Full Dose Reduction Potential of ASiRâ„¢ for Head CT Protocols in a Predominantly Pediatric Population
Authors: Mirro A , Brady S , Kaufman R 
Published: June 2015

Purpose:To ascertain and implement the maximum level of adaptive statistical iterative reconstruction (ASiR) that can be used to establish dose reduced pediatric head CT protocols.Methods:Noise power spectrum (NPS), modulation transfer function (MTF), and qualitative visual assessment were used as image quality metrics to calculate image quality based on filtered back projection (FBP) and ASiR reconstruction. The effect on image quality as a function of level of ASiR implementation and tube current reduction was analyzed by comparing image noise magnitude and frequency, and spatial resolution with similar measured image quality for FBP. Relative patient dose reduction was estimated using both CTDIvol and effective dose calculated using pediatric sized physical anthropomorphic phantoms. Dose reduced protocols were investigated for CT head examinations (i.e. brain, orbits, sinus, maxillary and temporal bones) by implementing ASiR and lowering CT tube current.Results:An analysis of the effects on noise texture from implementation of statistical iterative reconstruction determined that the level of ASiR that correlated closest with FBP for the GE soft reconstruction kernel (for both 100 and 120 kVp) was determined to be 30%, and for the GE standard reconstruction kernel at 100 kVp was 20% ASiR. However, implementation of 60% ASiR (GE soft reconstruction kernel) and 30% ASiR (GE standard reconstruction kernel) led to an average relative reduction in CTDIvol by 40% (range: 30%‐47%) and effective dose by 36% (range: 12%‐54%) while maintaining the same overall noise magnitude and improving the CNR of the image as compared to FBP. A coarser noise texture was visualized at 60% ASiR.Conclusion:The data in this study are provided to allow customized selection of ASiR implementation relating to acceptable tolerance for change in noise texture appearance in reconstructed images, and level of relative dose reduction for a pediatric population undergoing head CT examination.
TH‐EF‐BRA‐06: A Novel Method of ACR Dose Index Registry Report Interpretation: Population Dose Reduction for Thoracic CT Angiography
Authors: Zamora D , Robinson J , Kanal K 
Published: June 2015

Purpose:To identify a method of ACR Dose Index Registry (DIR) report analysis and interpretation that focuses dose reduction efforts on exams that most affect our patient population.Methods:In place of a direct interpretation of the DIR report, a proposed additional metric — the Total Exposure Variance (TEV) — was calculated for each of the most frequently performed institutional exams. TEV was defined as the product of exam frequency (N) and the difference between institutional and national median dose (CTDIvol or SSDE). TEV indicated total excess institution population dose beyond the equivalent national benchmark. TEV analysis focused investigation of two exams from the 2012 DIR report: 1) CT pulmonary angiography (CTPA), which had SSDE between the median and third quartile; and, 2) CT thoracic angiography (CTTA), optimized for the aorta, which had SSDE in the top quartile.Results:CT scan parameter changes were implemented lowering the quality reference mAs by 20% and limiting the automatic kV selection range to 100–120. DIR data from July–December 2012 were compared to same time period for 2013. CTPA showed a decrease of median CTDIvol and SSDE of 14% and 16%, respectively, representing a realized decrease in TEV of 1776 mGy‐persons. Data for CTTA showed a decrease of median CTDIvol and SSDE of 38% and 44%, respectively, representing a realized decrease in TEV of 1050 mGy‐persons. In both cases, the incremental and population dose metrics moved down toward national benchmarks.Conclusion:TEV analysis used DIR data to shift the paradigm toward reducing population dose instead of frequency‐independent interpretation of the report. The TEV metric highlighted exams that would have otherwise been overlooked with direct DIR report interpretation. Recent modifications to the DIR report contents may avail additional approaches to dose reduction.
TH‐EF‐BRA‐07: A Reference Organ Dose Database for Body CT Examination Based On AAPM 246
Authors: Tian X , Segars P , Andersson J , Pavlicek W , Samei E 
Published: June 2015

Purpose:This study aims to establish a reference organ dose database for clinical body CT based on detailed modeling of patient anatomy and irradiation condition.Methods:Clinical CT images of 40 adult patients (age range: 18–78 y.o., 22 male, 18 female) were included. Each patient received a chest and abdominopelvic CT examination at our institution. Whole‐body computer models were created from clinical CT data, which included most of the radiosensitive organs defined by ICRP Publication 103. A previously‐validated Monte Carlo program was used to simulate organ dose for each patient model. The scanner spectrum, geometry and material information of the bowtie filter, and the tube current modulation (TCM) profiles were explicitly modeled. Three examination conditions were modeled: (1) fixed tube current (2) TCM exams with modest modulation strength (alpha = 0.5), and (3) TCM exams with strong modulation strength (alpha = 1).The calculated organ dose values were provided as a reference database for dosimetry benchmarking for chest and abdominopelvic examinations.Results:Given the examination CTDIvol to be 7 mGy, organ dose for chest examination were in the range of 1.42 mGy to 14.4 mGy. For abdominopelvic examination, organ dose were in the range of 1.71 mGy to 10.5 mGy. Organ dose shows a gradual decrease with the increase of tube current modulation level. For chest scan, the average organ dose decreased 42.8% for the heart, and 25.0% for the lungs for strong modulation scans compared to no modulation. For abdominopelvic scan, the average organ dose decreased 33.8% for the stomach and 31.6% for the liver when implemented with strong TCM modulation compared to no modulation.Conclusion:A database of organ dose estimation is provided with information available for detailed modeling of the patient anatomy and scanner irradiation condition. Such database may be used as a reference standard in quantification and reporting of organ doses.Research fundings from GE, Siemens, and Carestream