bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐I‐75: Half‐Value Layer Thicknesses and Homogeneity Coefficients for Fluoroscopic X‐Ray Beam Spectra Incorporating Spectral Filtration
Authors: Wunderle K , Godley A , Shen Z , Rakowski J , Dong F 
Published: July 2016

Purpose:The purpose of this investigation is to quantify various first half‐value‐layers (HVLs), second HVLs and homogeneity coefficients (HCs) for a state‐of‐the‐art fluoroscope utilizing spectral (copper) filtration.Methods:A Radcal (Monrovia, Ca) AccuPro dosimeter with a 10×6‐6 calibrated ionization chamber was used to measure air kerma for radiographic x‐ray exposures made on a Siemens (Erlangen, Germany) Artis ZeeGo fluoroscope operated in the service mode. The ionization chamber was centered in the x‐ray beam at 72 cm from the focal spot with a source‐to‐image‐distance of 120 cm. The collimators were introduced to limit the x‐ray field to approximately 5 cm × 5 cm at the ionization chamber plane. Type‐1100 aluminum filters, in 0.5 mm increments, were used to determine the HVL. Two HVL calculation methods were used, log‐linear interpolation and Lambert‐W interpolation as described by Mathieu [Med Phys, 38(8), 4546 (2011)]. Multiple measurements were made at 60, 80, 100, 120 kVp at spectral filtration thicknesses of 0, 0.1, 0.3, 0.6 and 0.9 mm.Results:First HVL, second HVL, and HCs are presented for the fluoroscopic x‐ray beam spectra indicated above, with nearly identical results from the two interpolation methods. Accuracy of the set kVp was also determined and deviated less than 2%. First HVLs for fluoroscopic x‐ray beam spectra without spectral filtration determined in our study were 7%–16% greater than previously published data by Fetterly et al. [Med Phys, 28, 205 (2001)]. However, the FDA minimum HVL requirements changed since that publication, requiring larger HVLs as of 2006. Additionally, x‐ray tube and generator architecture have substantially changed over the last 15 years providing different beam spectra.Conclusion:X‐ray beam quality characteristics for state‐of‐the‐art fluoroscopes with spectral filtration have not been published. This study provides reference data which will be useful for defining beam qualities encountered on fluoroscopes using spectral filtration.
SU‐F‐I‐79: Validation of a Monte Carlo Radiographic Simulation
Authors: Gearhart A , Carver D , Stabin M 
Published: July 2016

Purpose:To validate a radiographic simulation in order to estimate patient dose due to clinically‐used radiography protocols.Methods:A Monte Carlo simulation was created to simulate a radiographic x‐ray beam using GEANT4. Initial validation was performed according to a portion of TG 195. Computational NURBS‐based phantoms were used simulate patients of varying ages and sizes. The deposited energy in the phantom is output by the simulation. The exposure in air from a clinically used radiography unit was measured at 100 cm for various tube potentials. 10 million photons were simulated with 1 cubic centimeter of air located 100 cm from the source, and the total absorbed dose was noted. The normalization factor was determined by taking a ratio of the measured dose in air to the simulated dose in air. Dose to individual voxels is calculated using the energy deposition map along with the voxelized and segmented phantom and the normalization factor. Finally, the effective dose is calculated using the ICRP methodology and tissue weighting factors.Results:This radiography simulation allows for the calculation and visualization of the energy deposition map within a voxelized phantom. The ratio of exposure, measured using an ionization chamber, to air in the simulation was determined. Since the simulation output is calibrated to match the exposure of a given clinical radiographic x‐ray tube, the dose map may be visualized. This will also allow for absorbed dose estimation in specific organs or tissues as well as a whole body effective dose estimation.Conclusion:This work indicates that our Monte Carlo simulation may be used to estimate the radiation dose from clinical radiographic protocols. This will allow for an estimate of radiographic dose from various examinations without the use of traditional methods such as thermoluminescent dosimeters and body phantoms.
SU‐F‐J‐02: Flexible Training of MR‐Guided Laser Ablation Models Via Global Optimization
Authors: Fahrenholtz SJ , Stafford RJ , Madankan R , Hazle JD , Fuentes D 
Published: July 2016

Purpose:MR‐guided laser ablation is currying interest in neurosurgery as a minimally invasive procedure. The procedure is planned via an assumed lesion overlaid on various anatomic and functional images. Computational models of heat transfer may further inform planning the intervention, reducing surgical morbidity and ensuring therapeutic effect. These models require physical parameter data, via less relevant literature values. Using commercialized laser ablation equipment combined with MR temperature imaging (MRTI) feedback, recent work has demonstrated the use of inverse problems as a means to gain the necessary information via retrospective analysis. Here, performance of a global inverse problem solution is explored that allows for simultaneous optimization of multiple objective functions.Methods:A steady state bioheat model is trained on MRTI patient datasets (n=20); the MRTI regions exceeding a 57°C threshold are considered lethally damaged. Optical and blood perfusion parameters are densely sampled, allowing for global optimization of the model. There are two objective functions to optimize with respect to damage prediction: Dice similarity coefficient (DSC) and Hausdorff distance (HD). DSC is an overlap metric; HD is the distance‐to‐agreement in physical distance. Predictive performance is simulated via leave‐one‐out cross‐validation (LOOCV) and is compared to the same model using naive literature values.Results:Post‐optimization and during LOOCV, mean and median DSC are 0.824 and 0.850 respectively; mean and median HD are 4.64mm and 4.03mm respectively. These compare favorably to the model using literature values. Mean and median DSC are 0.6685 and 0.6564 respectively; mean and median HD are 5.85mm and 5.58mm respectively. A two‐tailed paired Student's t‐test for the mean DSC reported p=0.0002. For mean HD, p=0.0064.Conclusion:Clinical MRTI feedback provides useful information for designing optimized laser ablation models. Global optimization facilitates simultaneous optimization of multiple objective functions. Trained models are considerably more accurate than naive literature based models as measured by DSC and HD.
SU‐F‐J‐14: Kilovoltage Cone‐Beam CT Dose Estimation of Varian On‐Board Imager Using GMctdospp Monte Carlo Framework
Authors: Kim S , Rangaraj D 
Published: July 2016

Purpose:Although cone‐beam CT (CBCT) imaging became popular in radiation oncology, its imaging dose estimation is still challenging. The goal of this study is to assess the kilovoltage CBCT doses using GMctdospp ‐ an EGSnrc based Monte Carlo (MC) framework.Methods:Two Varian OBI x‐ray tube models were implemented in the GMctpdospp framework of EGSnrc MC System. The x‐ray spectrum of 125 kVp CBCT beam was acquired from an EGSnrc/BEAMnrc simulation and validated with IPEM report 78. Then, the spectrum was utilized as an input spectrum in GMctdospp dose calculations. Both full and half bowtie pre‐filters of the OBI system were created by using egs_prism module. The x‐ray tube MC models were verified by comparing calculated dosimetric profiles (lateral and depth) to ion chamber measurements for a static x‐ray beam irradiation to a cuboid water phantom. An abdominal CBCT imaging doses was simulated in GMctdospp framework using a 5‐year‐old anthropomorphic phantom. The organ doses and effective dose (ED) from the framework were assessed and compared to the MOSFET measurements and convolution/superposition dose calculations.Results:The lateral and depth dose profiles in the water cuboid phantom were well matched within 6% except a few areas ‐ left shoulder of the half bowtie lateral profile and surface of water phantom. The organ doses and ED from the MC framework were found to be closer to MOSFET measurements and CS calculations within 2 cGy and 5 mSv respectively.Conclusion:This study implemented and validated the Varian OBI x‐ray tube models in the GMctdospp MC framework using a cuboid water phantom and CBCT imaging doses were also evaluated in a 5‐year‐old anthropomorphic phantom. In future study, various CBCT imaging protocols will be implemented and validated and consequently patient CT images will be used to estimate the CBCT imaging doses in patients.
SU‐F‐J‐15: The Use of CBCT for Dose Calculations in H/N Patients: Impact of Limited FOV
Authors: Rosen B , Lee C , Brock K 
Published: July 2016

Purpose:To investigate the impact of limited superior and inferior (SI) field‐of‐view (FOV) associated with on‐board kV CBCT images for dose calculation.Methods:First, a (10×10) cm2 continuous arc 6 MV treatment plan was calculated for fourteen virtual water phantoms of varying SI thicknesses (5 to 15 cm) to replicate the FOV effect. In addition, 70 Gy VMAT plans from two H/N patients were calculated on their corresponding planning CT (pCT) and first fraction CBCT image volumes. For the phantom, the mean dose difference (full vs. limited FOV phantom) was calculated for each axial plane for each size phantom to determine the error with distance from the SI boundary, as a function of dose at the FOV edge. For the clinical cases, the absolute difference between CBCT and pCT dose was calculated for each voxel within the CBCT FOV and evaluated relative to CBCT SI boundary.Results:Phantom calculations showed that mean error was less than 5% for all planes whenever the CBCT border received less than 35 Gy or, otherwise, in planes at least 1.5 cm inside the CBCT SI FOV. Maximum pCT‐calculated doses differences in the axial plane of the superior CBCT FOV border was 4 Gy for Patient 1 and 55 Gy for Patient 2, and the corresponding maximum error in the same planes were 2% and 24%, respectively. Maximum pCT‐calculated dose 1 cm inferior to the superior FOV border was 7 Gy and 72 Gy, with a corresponding error of 0.5% and 2.5%.Conclusion:CBCT images may be used as a surrogate for full CT images with the following limitations: low dose (<50% of prescription dose) at the FOV edge, or greater than 1.5 cm material thickness between the CBCT border and the axial plane of interest.This work was partially funded by NIH P01CA059827.
SU‐F‐J‐23: Field‐Of‐View Expansion in Cone‐Beam CT Reconstruction by Use of Prior Information
Authors: Haga A , Magome T , Nakano M , Kotoku J , Nakagawa K 
Published: July 2016

Purpose:Cone‐beam CT (CBCT) has become an integral part of online patient setup in an image‐guided radiation therapy (IGRT). In addition, the utility of CBCT for dose calculation has actively been investigated. However, the limited size of field‐of‐view (FOV) and resulted CBCT image with a lack of peripheral area of patient body prevents the reliability of dose calculation. In this study, we aim to develop an FOV expanded CBCT in IGRT system to allow the dose calculation.Methods:Three lung cancer patients were selected in this study. We collected the cone‐beam projection images in the CBCT‐based IGRT system (X‐ray volume imaging unit, ELEKTA), where FOV size of the provided CBCT with these projections was 410 × 410 mm2 (normal FOV). Using these projections, CBCT with a size of 728 × 728 mm2 was reconstructed by a posteriori estimation algorithm including a prior image constrained compressed sensing (PICCS). The treatment planning CT was used as a prior image. To assess the effectiveness of FOV expansion, a dose calculation was performed on the expanded CBCT image with region‐of‐interest (ROI) density mapping method, and it was compared with that of treatment planning CT as well as that of CBCT reconstructed by filtered back projection (FBP) algorithm.Results:A posteriori estimation algorithm with PICCS clearly visualized an area outside normal FOV, whereas the FBP algorithm yielded severe streak artifacts outside normal FOV due to under‐sampling. The dose calculation result using the expanded CBCT agreed with that using treatment planning CT very well; a maximum dose difference was 1.3% for gross tumor volumes.Conclusion:With a posteriori estimation algorithm, FOV in CBCT can be expanded. Dose comparison results suggested that the use of expanded CBCTs is acceptable for dose calculation in adaptive radiation therapy.This study has been supported by KAKENHI (15K08691).
SU‐F‐J‐34: Automatic Target‐Based Patient Positioning Framework for Image‐Guided Radiotherapy in Prostate Cancer Treatment
Authors: Sasahara M , Arimura H , Shibayama Y , Hirose T , Ohga S , Umezu Y , Honda H , Sasaki T 
Published: July 2016

Purpose:Current image‐guided radiotherapy (IGRT) procedure is bonebased patient positioning, followed by subjective manual correction using cone beam computed tomography (CBCT). This procedure might cause the misalignment of the patient positioning. Automatic target‐based patient positioning systems achieve the better reproducibility of patient setup. Our aim of this study was to develop an automatic target‐based patient positioning framework for IGRT with CBCT images in prostate cancer treatment.Methods:Seventy‐three CBCT images of 10 patients and 24 planning CT images with digital imaging and communications in medicine for radiotherapy (DICOM‐RT) structures were used for this study. Our proposed framework started from the generation of probabilistic atlases of bone and prostate from 24 planning CT images and prostate contours, which were made in the treatment planning. Next, the gray‐scale histograms of CBCT values within CTV regions in the planning CT images were obtained as the occurrence probability of the CBCT values. Then, CBCT images were registered to the atlases using a rigid registration with mutual information. Finally, prostate regions were estimated by applying the Bayesian inference to CBCT images with the probabilistic atlases and CBCT value occurrence probability. The proposed framework was evaluated by calculating the Euclidean distance of errors between two centroids of prostate regions determined by our method and ground truths of manual delineations by a radiation oncologist and a medical physicist on CBCT images for 10 patients.Results:The average Euclidean distance between the centroids of extracted prostate regions determined by our proposed method and ground truths was 4.4 mm. The average errors for each direction were 1.8 mm in anteroposterior direction, 0.6 mm in lateral direction and 2.1 mm in craniocaudal direction.Conclusion:Our proposed framework based on probabilistic atlases and Bayesian inference might be feasible to automatically determine prostate regions on CBCT images.
SU‐F‐J‐35: Moving Towards Isocentric Prone Breast Setup with Contralateral Leveling Tattoo and Couch Move Assistant (CMA)
Authors: Yang K , Downey C , Suter N , Gott L , Naughton L , Aufiero K , Day S , McGovern N , Brock J , Andreou K , Strasser J , Koprowski C , Raben A , Chen H , Mourtada F 
Published: July 2016

Purpose:Large setup variability has been observed for prone breast patients due to rotation error. To reduce this uncertainty, we propose a novel implementation of isocentric prone breast method on Elekta linac with couch move assistant (CMA) and on‐line KV CBCT.Methods:Daily CBCT is used to evaluate the prone breast patient positioning uncertainty of proposed isocentric technique against our routine manual clinical setup. Clinical setup involves a manual AP shift from the ipsilateral torso tattoos (2PT) to the treatment iso directly underneath and SSD and flash check. While the proposed isocentric prone breast method features an additional contralateral leveling tattoo positioned at mid‐level of torso during CT simulation to determine correct patient obliqueness, and an automatic couch shift using Elekta CMA to correct both known distance from 2PT to the iso and daily setup uncertainty. Summary statistics were calculated for a cohort of prone breast patients from our clinic (n=5), and will be updated as more patients get administrated.Results:Small field of view partial CBCT acquisition is optimized to achieve clearance and minimize nominal imaging dose to 0.6cGy per scan to a 16cm phantom. Routine clinical setup uncertainty is 0.3±0.2cm, 0.7±0.4cm and 0.4±0.3cm in S/I, L/R and A/P respectively. Using the isocentric prone breast method, the setup uncertainty could be reduced to 0±0.3cm, 0.3±0.4cm and 0.1±0.3cm if the average couch shift in the 1st week of treatment is applied by CMA to the rest of treatment days. The uncertainty could be further reduced to 0.3±0.1cm, 0±0.1cm and 0±0.2cm with additional contralateral leveling tattoo. The improvement in precision is found to be statistically significant (p<0.05) using unpaired student t‐tests.Conclusion:Contralateral leveling tattoo is essential to determine correct patient obliqueness. More consistent and accurate isocentric prone breast patient positioning is achievable on Elekta linac with CMA and CBCT.
SU‐F‐J‐42: Comparison of Varian TrueBeam Cone‐Beam CT and BrainLab ExacTrac X‐Ray for Cranial Radiotherapy
Authors: Li J , Shi W , Andrews D , Werner‐Wasik M , Lu B , Yu Y , Dicker A , Liu H 
Published: July 2016

Purpose:To compare online image registrations of TrueBeam cone‐beam CT (CBCT) and BrainLab ExacTrac x‐ray imaging systems for cranial radiotherapy.Method:Phantom and patient studies were performed on a Varian TrueBeam STx linear accelerator (Version 2.5), which is integrated with a BrainLab ExacTrac imaging system (Version 6.1.1). The phantom study was based on a Rando head phantom, which was designed to evaluate isocenter‐location dependence of the image registrations. Ten isocenters were selected at various locations in the phantom, which represented clinical treatment sites. CBCT and ExacTrac x‐ray images were taken when the phantom was located at each isocenter. The patient study included thirteen patients. CBCT and ExacTrac x‐ray images were taken at each patient's treatment position. Six‐dimensional image registrations were performed on CBCT and ExacTrac, and residual errors calculated from CBCT and ExacTrac were compared.Results:In the phantom study, the average residual‐error differences between CBCT and ExacTrac image registrations were: 0.16±0.10 mm, 0.35±0.20 mm, and 0.21±0.15 mm, in the vertical, longitudinal, and lateral directions, respectively. The average residual‐error differences in the rotation, roll, and pitch were: 0.36±0.11 degree, 0.14±0.10 degree, and 0.12±0.10 degree, respectively. In the patient study, the average residual‐error differences in the vertical, longitudinal, and lateral directions were: 0.13±0.13 mm, 0.37±0.21 mm, 0.22±0.17 mm, respectively. The average residual‐error differences in the rotation, roll, and pitch were: 0.30±0.10 degree, 0.18±0.11 degree, and 0.22±0.13 degree, respectively. Larger residual‐error differences (up to 0.79 mm) were observed in the longitudinal direction in the phantom and patient studies where isocenters were located in or close to frontal lobes, i.e., located superficially.Conclusion:Overall, the average residual‐error differences were within 0.4 mm in the translational directions and were within 0.4 degree in the rotational directions.
SU‐F‐J‐51: A Cone‐Based Scintillator Detector for IGRT QA for Scattered and Scanning Proton Therapy
Authors: Oesten H , Clasie B , Nelson B , Jee K 
Published: July 2016

Purpose:IGRT commissioning and QA are critical components for precise delivery of proton treatment beams to patients. In order to ensure high quality IGRT, a new cone‐based scintillator detector was evaluated for our QA activities for double‐scattered and scanning proton modalities. This allows a routine evaluation of the gantry‐angle dependent position offset between the radiation and imaging.Methods:The cone‐based scintillator detector (XRV‐124, Logos Systems, Int'l CA, USA) features a unique configuration of measuring stereotactic paths of proton and x‐ray beams in a single setup with arbitrary gantry angles. For the beams‐eye‐view (BEV) analysis of x‐ray crosshair images, a cylindrical representation of the cone image was newly developed. The calibration accuracy was evaluated using different CT resolutions for a range of 55 – 95mm in patient's cranial direction and ±9mm in the lateral direction. Energy‐dependent spot sizes (σ) of pencil beams were characterized and compared to measurements by the MatriXX detector (IBA, Germany). Iso‐centric deviations between radiation and x‐ray imaging were characterized as a function of gantry angle.Results:The position calibration of the detector was successfully verified with a reproducible positioning by x‐ray imaging. The measurements were reproducible within clinical tolerances (±1mm). The spot size vs. energy at zero gantry angle measured with the scintillating cone detector agreed with the MatriXX detector measurements within 17%.Conclusion:The new approach to investigate the accuracy of IGRT and pencil beam properties could successfully be implemented into the QA program. The system will improve efficiency in our QA activities for proton treatments.
SU‐F‐J‐59: Assessment of Dose Response Distribution in Individual Human Tumor
Authors: Yan D , Chen S , Krauss D , Chen P , Wilson G 
Published: July 2016

Purpose:To fulfill precision radiotherapy via adaptive dose painting by number, voxel‐by‐voxel dose response or radio‐sensitivity in individual human tumor needs to be determined in early treatment to guide treatment adaptation. In this study, multiple FDG PET images obtained pre‐ and weekly during the treatment course were utilized to determine the distribution/spectrum of dose response parameters in individual human tumors.Methods:FDG PET/CT images of 18 HN cancer patients were used in the study. Spatial parametric image of tumor metabolic ratio (dSUV) was created following voxel by voxel deformable image registration. Each voxel value in dSUV was a function of pre‐treatment baseline SUV and treatment delivered dose, and used as a surrogate of tumor survival fraction (SF). Regression fitting with break points was performed using the LQ‐model with tumor proliferation for the control and failure group of tumors separately. The distribution and spectrum of radiation sensitivity and growth in individual tumors were determined and evaluated.Results:Spectrum of tumor dose‐sensitivity and proliferation in the controlled group was broad with α in tumor survival LQ‐model from 0.17 to 0.8. It was proportional to the baseline SUV. Tlag was about 21∼25 days, and Tpot about 0.56∼1.67 days respectively. Commonly tumor voxels with high radio‐sensitivity or larger α had small Tlag and Tpot. For the failure group, the radio‐sensitivity α was low within 0.05 to 0.3, but did not show clear Tlag. In addition, tumor voxel radio‐sensitivity could be estimated during the early treatment weeks.Conclusion:Dose response distribution with respect to radio‐sensitivity and growth in individual human tumor can be determined using FDG PET imaging based tumor metabolic ratio measured in early treatment course. The discover is critical and provides a potential quantitative objective to implement tumor specific precision radiotherapy via adaptive dose painting by number.