bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐671: Effects of Collimator Material On Proton Minibeams
Authors: Lee E , Eagle J , Sandison G , Cao N , Stewart R , Marsh S , Meyer J 
Published: July 2016

Purpose:To investigate the dosimetric effects of collimator material on spatially modulated proton minibeams (pMBRT). Methods: pMBRT holds promise to exhibit shallow depth normal‐tissue sparing effects similar to synchrotron based microbeams while also retaining potential for uniform dose distributions for tumor targets. TOPAS Monte Carlo simulations were performed for a 5cm thick multislit collimator with 0.3mm slits and 1mm center‐to‐center spacing for a 50.5MeV proton minibeam while varying collimator material between brass, tungsten, and iron. The collimator was placed both “flush” at the water phantom surface and at 5cm distance to investigate the effects on surface dose, peak‐to‐valley‐dose‐ratio (PVDR) and neutron contribution.Results:For flush placement, the neutron dose at the phantom surface for the tungsten collimator was approximately 20% higher than for brass and iron. This was not reflected in the overall surface dose, which was comparable for all materials due to the relatively low neutron contribution of <0.1%. When the collimator was retracted, the overall neutron contribution was essentially identical for all three collimators. Surface dose dropped by ∼40% for all collimator materials with air gap compared to being flush with the phantom surface. This surface dose reduction was at the cost of increase in valley dose for all collimator materials due to increased angular divergence of the mini‐beams at the surface and their consequent geometric penumbra at depth. When the collimator was placed at distance from the phantom surface the PVDR decreased. The peak‐to‐entrance‐dose ratio was highest for the iron collimator with 5cm air gap. Conclusion: The dosimetric difference between the collimator materials is minimal despite the relatively higher neutron contribution at the phantom surface for the tungsten collimator when placed flush. The air gap between the collimator and phantom surface strongly influences all dosimetry parameters due to the influence of scatter on the narrow spatial modulation.
SU‐G‐BRA‐03: PCA Based Imaging Angle Optimization for 2D Cine MRI Based Radiotherapy Guidance
Authors: Chen T , Yue N , Jabbour S , Zhang M 
Published: July 2016

Purpose:To develop an imaging angle optimization methodology for orthogonal 2D cine MRI based radiotherapy guidance using Principal Component Analysis (PCA) of target motion retrieved from 4DCT.Methods:We retrospectively analyzed 4DCT of 6 patients with lung tumor. A radiation oncologist manually contoured the target volume at the maximal inhalation phase of the respiratory cycle. An object constrained deformable image registration (DIR) method has been developed to track the target motion along the respiration at ten phases. The motion of the center of the target mass has been analyzed using the PCA to find out the principal motion components that were uncorrelated with each other. Two orthogonal image planes for cineMRI have been determined using this method to minimize the through plane motion during MRI based radiotherapy guidance.Results:3D target respiratory motion for all 6 patients has been efficiently retrieved from 4DCT. In this process, the object constrained DIR demonstrated satisfactory accuracy and efficiency to enable the automatic motion tracking for clinical application. The average motion amplitude in the AP, lateral, and longitudinal directions were 3.6mm (min: 1.6mm, max: 5.6mm), 1.7mm (min: 0.6mm, max: 2.7mm), and 5.6mm (min: 1.8mm, max: 16.1mm), respectively. Based on PCA, the optimal orthogonal imaging planes were determined for cineMRI. The average angular difference between the PCA determined imaging planes and the traditional AP and lateral imaging planes were 47 and 31 degrees, respectively. After optimization, the average amplitude of through plane motion reduced from 3.6mm in AP images to 2.5mm (min:1.3mm, max:3.9mm); and from 1.7mm in lateral images to 0.6mm (min: 0.2mm, max:1.5mm), while the principal in plane motion amplitude increased from 5.6mm to 6.5mm (min: 2.8mm, max: 17mm).Conclusion:DIR and PCA can be used to optimize the orthogonal image planes of cineMRI to minimize the through plane motion during radiotherapy guidance.
SU‐G‐BRA‐09: Estimation of Motion Tracking Uncertainty for Real‐Time Adaptive Imaging
Authors: Yan H , Chen Z , Nath R , Liu W 
Published: July 2016

Purpose:kV fluoroscopic imaging combined with MV treatment beam imaging has been investigated for intrafractional motion monitoring and correction. It is, however, subject to additional kV imaging dose to normal tissue. To balance tracking accuracy and imaging dose, we previously proposed an adaptive imaging strategy to dynamically decide future imaging type and moments based on motion tracking uncertainty. kV imaging may be used continuously for maximal accuracy or only when the position uncertainty (probability of out of threshold) is high if a preset imaging dose limit is considered. In this work, we propose more accurate methods to estimate tracking uncertainty through analyzing acquired data in real‐time.Methods:We simulated motion tracking process based on a previously developed imaging framework (MV + initial seconds of kV imaging) using real‐time breathing data from 42 patients. Motion tracking errors for each time point were collected together with the time point's corresponding features, such as tumor motion speed and 2D tracking error of previous time points, etc. We tested three methods for error uncertainty estimation based on the features: conditional probability distribution, logistic regression modeling, and support vector machine (SVM) classification to detect errors exceeding a threshold.Results:For conditional probability distribution, polynomial regressions on three features (previous tracking error, prediction quality, and cosine of the angle between the trajectory and the treatment beam) showed strong correlation with the variation (uncertainty) of the mean 3D tracking error and its standard deviation: R‐square = 0.94 and 0.90, respectively. The logistic regression and SVM classification successfully identified about 95% of tracking errors exceeding 2.5mm threshold.Conclusion:The proposed methods can reliably estimate the motion tracking uncertainty in real‐time, which can be used to guide adaptive additional imaging to confirm the tumor is within the margin or initialize motion compensation if it is out of the margin.
SU‐G‐BRA‐12: Development of An Intra‐Fractional Motion Tracking and Dose Reconstruction System for Adaptive Stereotactic Body Radiation Therapy in High‐Risk Prostate Cancer
Authors: Rezaeian N Hassan , Chi Y , Tian Z , Jiang S , Hannan R , Jia X 
Published: July 2016

Purpose:A clinical trial on stereotactic body radiation therapy (SBRT) for high‐risk prostate cancer is undergoing at our institution. In addition to escalating dose to the prostate, we have increased dose to intra‐prostatic lesions. Intra‐fractional prostate motion deteriorates well planned radiation dose, especially for the small intra‐prostatic lesions. To solve this problem, we have developed a motion tracking and 4D dose‐reconstruction system to facilitate adaptive re‐planning.Methods:Patients in the clinical trial were treated with VMAT using four arcs and 10 FFF beam. KV triggered x‐ray projections were taken every 3 sec during delivery to acquire 2D projections of 3D anatomy at the direction orthogonal to the therapeutic beam. Each patient had three implanted prostate markers. Our developed system first determined 2D projection locations of these markers and then 3D prostate translation and rotation via 2D/3D registration of the markers. Using delivery log files, our GPU‐based Monte Carlo tool (goMC) reconstructed dose corresponding to each triggered image. The calculated 4D dose distributions were further aggregated to yield the delivered dose.Results:We first tested each module in our system. MC dose engine were commissioned to our treatment planning system with dose difference of <0.5%. For motion tracking, 1789 kV projections from 7 patients were acquired. The 2D marker location error was <1 mm. For 3D motion tracking, root mean square (RMS) errors along LR, AP, and CC directions were 0.26mm, 0.36mm, and 0.01mm respectively in simulation studies and 1.99mm, 1.37mm, and 0.22mm in phantom studies. We also tested the entire system workflow. Our system was able to reconstruct delivered dose.Conclusion:We have developed a functional intra‐fractional motion tracking and 4D dose re‐construction system to support our clinical trial on adaptive high‐risk prostate cancer SBRT. Comprehensive evaluations have shown the capability and accuracy of our system.
SU‐G‐206‐02: Impact of Focal Spot Sizes On CT Image Quality
Authors: Bache S , Rong J 
Published: July 2016

Purpose:To quantify a radiology team's assessment of image quality differences between two CT scanner models currently in clinical use, with emphasis on spatial resolution that could be impacted by focal spot size.Methods:Modulation Transfer Functions (MTF) measurements were performed by scanning the impulse source insert module of the Catphan 600 at 120/140 kVp with both large (LFS) and small (SFS) focal spots and reconstructed to 2.5mm and 5.0mm thicknesses on a GE Discovery CT750 HD and a LightSpeed VCT CT scanner. MTFs were calculated by summing the 2D PSF along one‐dimension to obtain line‐spread‐function (LSF), and calculating the Fourier Transform of the zero‐padded and background corrected LSF. Spatial resolution performance was evaluated by comparing MTF curves, 50% and 10% MTF cutoff, and total area under the MTF curve (AUC). In addition, images of the Catphan high‐contrast module and a Kagaku anthropomorphic body phantom were acquired from the HD scanner for visual comparisons.Results:For each scanner model, SFS was superior to LFS spatial resolution with respect to 50%/10% MTF cutoff and AUC. For the HD, 50%/10% cutoff was 4.29/7.22cm‐1 for the LFS and 4.43/7.45cm‐1 for the SFS. VCT outperformed HD, with 50%/10% cutoff of 4.40/7.29 cm‐1 for LFS and 4.62/7.47cm‐1 for SFS. Scanner model performance in order of decreasing AUC performance was VCT SFS (7.43), HD SFS (7.20), VCT LFS (7.09) and HD LFS (6.93). Visual evaluations of Kagaku phantom images confirmed that VCT outperformed HD.Conclusion:VCT outperformed HD and small focal spot is desired for either model over large focal spot in term of spatial resolution – in agreement with radiologist feedback of overall image quality. In‐depth evaluations of clinical impact and focal spot selection mechanisms is currently being assessed.
SU‐G‐206‐09: Consistent Low Contrast Detectability and Optimal Dose for Different Patient Sizes in Abdominal CT
Authors: Zhou Y , Nute J , Scott A , Lee C 
Published: July 2016

Purpose:To study optimal dose dictated by consistent low contrast detectability for various patient sizes in abdominal CT.Methods:Seven realistically shaped tissue‐equivalent abdomen phantoms (CIRS TE01–TE08) were utilized. Helical scans were performed on each phantom with GE 750 HD and Siemens mCT 64 at different dose levels. The images were reconstructed using comparable kernels (standard and Bf35 for GE and Siemens, respectively). The noise images, obtained using subtraction from adjacent slices, were partitioned into matrices of square cells matching different sizes of lesions (1.8 – 10 mm). The noise granularities were quantified by the standard deviation (σ) of the matrix cell pixel mean values distribution at each cell size. The minimum detectable contrast (MDC), defined as 3.29σ with 95% confidence of detectability, was obtained for each phantom at different doses. We proposed that the MDC is inversely proportional to the lesion size and to the square root of the size specific dose and the proportional factor is a function of phantom size. The MDC data was fitted against the lesion size and dose following the proposed model.Results:The simplified power law model was found to fit the minimum detectable contrast against the lesion and dose very well for various phantoms (R^2 > 0.983). The proportionality factor was found to fit the phantom equivalent diameter (L) to a Gaussian amplifier with R2 = 0.983 and to an exponential function with R^2 = 0.999, for GE HD750 and Siemens mCT 64, respectively. The parameters of the Gaussian amplifier varied with different scanners. To obtain the tube current‐rotation time product (mAs) from the size specific dose (D), the relationship of D per 100 mAs versus L at 120 kVp was also presented for each scanner.Conclusion:The relationship of low contrast detectability and optimal dose across different patient sizes was successfully obtained.
SU‐G‐206‐10: Low‐Contrast Detectability Vs. Dose for CT Images Reconstructed Using Filtered Backprojection and Iterative Reconstruction: Assessment with a Model Observer
Authors: Favazza C , Ferrero A , McMillan K , Bruesewitz M , Yu L , Leng S , Kofler J , McCollough C 
Published: July 2016

Purpose:To evaluate CT low‐contrast detectability at different dose levels in images reconstructed using filtered backprojection (FBP) and iterative reconstruction (IR).Methods:A validated channelized Hotelling observer (CHO) model was used to detect low contrast objects in images of a helical CT phantom (Model 061, CIRS) using an Aquilion Prime 160 scanner (Toshiba Medical Systems). Twenty‐one different objects of 7 diameters (2.4, 3.2, 4.6, 6.3, 9.5, and 10 mm) and 3 contrast levels (∼10, 15, and 25 HU) were evaluated. Images were acquired using 5 different tube current settings (45, 60, 90, 140, and 180 mA) and reconstructed using both FBP and IR (Adaptive Iterative Dose Reduction (AIDR) 3D). For each tube current, the phantom was scanned 100 times, yielding sets of 100 object‐present and object‐absent images at the same x‐y locations. All images were evaluated using the CHO and detectability indices (d’) for each object were calculated at all dose levels.Results:For the same tube current setting, images formed using IR yielded d’ values on average 8% higher than images reconstructed using FBP. When dose was reduced by more than 25% of the full dose, however, results showed reduced low‐contrast detectability in AIDR‐3D images compared to 100% dose, FBP images. With the vendordefault settings, dose is automatically reduced by 70‐75% when AIDR 3D reconstructions are selected, which our data indicate would significantly reduce low contrast detectability.Conclusion:At higher dose levels (minimal dose reduction), AIDR‐3D improved object detectability as compared to full‐dose FBP images. However, when dose was reduced by more than 25%, object detectability was substantially reduced for images reconstructed with AIDR‐3D compared to full‐dose FBP images.CH McCollough is supported by industry funding from Siemens Healthcare
SU‐G‐206‐12: The Correlation Between Table Height and Patient Size in CT: A Simple Way to Properly Position Patients
Authors: Szczykutowicz T , Janssen‐Saldivar E , Miller D , Malkus A 
Published: July 2016

Purpose:Proper patient positioning is essential in CT to ensure automatic exposure control functions properly, noise uniformity, and CT number uniformity. This work describes how table height can be used as a surrogate for proper patient positioning and motivates incorporating table height recommendations as a function of patient size into technologist training programs.Methods:Scan data were acquired from 551 adult and pediatric patients under IRB approval. The table height, mean anterior‐posterior patient dimension, and mean lateral patient dimension were calculated for each patient. Table height as a function of a patient size surrogate was then analyzed. The mathematical relationship between table height and a properly positioned cylinder was derived and used to fit the data. Patient scans showing proper positioning, and positioning both too high and too low in the gantry were analyzed by measuring the image noise within anterior and posterior regions of the liver.Results:The slope of our fits to patient data matched the mathematical model well, suggesting our technologists are on average properly positioning patients at isocenter. The predicted slope for table height versus anterior‐posterior width is 0.5; we measured 0.48±0.006. Patients with table heights more than 2 sigma from the mean table height for their size were shown to have noise non‐uniformities greater than 13 HU across the liver which demonstrates how knowing the patient size and table height can predict the image quality of the subsequent CT exam.Conclusion:Our results motivate training technologists to pay attention to the table height. Doing so could easily stop an adult receiving a pediatric positioning and vice versa. Additionally, our results can guide the construction of low end CT scanners lacking vertical table motion by defining the range of table heights used at our clinical practice for a particular patient age and size.Research support provided by GE Healthcare. TPS supplies CT protocols to GE Healthcare under a licensing agreement.
SU‐G‐IeP1‐12: Size Selective Arterial Cerebral Blood Volume Mapping Using Multiple Inversion Time Arterial Spin Labeling
Authors: Jung Y , Johnston M , Liu H , Whitlow C 
Published: July 2016

Purpose:To demonstrate the feasibility of a novel method for size specific arterial cerebral blood volume (aCBV) mapping using pseudo‐continuous arterial spin labeling (PCASL), with multiple TI.Methods:Multiple PCASL images were obtained from a subject with TI of [300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000, 3500, 4000] ms. Each TI pair was averaged six times. Two scans were performed: one without a flow crusher gradient and the other with a crusher gradient (10cm/s in three directions) to remove signals from large arteries. Scan times were 5min. without a crusher gradient and 5.5 min with a crusher gradient. Non‐linear fitting algorithm finds the minimum mean squared solution of per‐voxel based aCBV, cerebral blood flow, and arterial transit time, and fits the data into a hemodynamic model that represents superposition of blood volume and flow components within a single voxel.Results:aCBV maps with a crusher gradient represent signals from medium and small sized arteries, while those without a crusher gradient represent signals from all sized arteries, indicating that flow crusher gradients can be effectively employed to achieve size‐specific aCBV mapping. Regardless of flow crusher, the CBF and ATT maps are very similar in appearance.Conclusion:Quantitative size selective blood volume mapping controlled by a flow crusher is feasible without additional information because the ASL quantification process doesn't require an arterial input function measured from a large artery. The size specific blood volume mapping is not interfered by sSignals from large arteries do not interfere with size specific aCBV mapping in the applications of interest in for applications in which only medium or small arteries are of interest.
SU‐G‐IeP1‐14: The Relationship Between Voxel Based Morphometry and Fiber Tract Abnormalities by Correlation Analysis in Patients with Neurodegerative Disease
Authors: Juh R , Suh T , Han J , Kim C , Oh C 
Published: July 2016

Purpose:We evaluated the relationship between white matter (WM) tract disintegration and gray matter (GM) atrophy in patients with Alzheimer's disease (AD), mild cognitive impairment (MCI) and controls, using diffusion tensor imaging (DTI) and an optimized voxel‐based analysis.Methods:Two hundred thirty one individuals (61 controls, 116 MCI and 54 AD) were included. Voxel‐based WM tract statistics was used to obtain whole‐brain maps of WM bundles for FA. Voxel‐based morphometry (VBM) was conducted to detect regions of gray matter (GM) atrophy in the AD, MCI group relative to the control group. FA maps were processed to make voxel‐wise comparison of tract based analysis in whole brain between each the two groups. The relationship between locations of abnormalities in the WM and GM were examined.Results:Patients with AD showed significant GM atrophy in posterior cingulate gyrus (BA31, 32) to the precuneus, the middle temporal lobe (BA19), the superior frontal (BA9) to the anterior cingulate (BA 32), the medial frontal lobe (BA 11, BA25), the hippocampus, the parahippocampal gyrus (BA30/34) and the insula, and WM tract disintegrity of the uncinate fasciculus, posterior cingulate fasciculus and fornix compared with the control and MCI groups. These abnormalities in the AD group were caused by either structural changes in GM atrophy or neural dysfunction due to functional disconnections in the WM tract.Conclusion:The GM atrophy resulting from WM tract disintegration or GM atrophy itself may be the first step in the AD process, resulting in anatomically congruent correlations between WM disintegration and regional GM atrophy. Using tract based spatial statistics and voxel based analysis, both of which are useful in investigating GM and WM changes in individuals with neurodegenerative disorders.
SU‐G‐JeP1‐02: A New Intra‐Fractional Prostate Motion Tracking Method in Volumetric Modulated Arc Therapy (VMAT) Via 2D/3D Registration
Authors: Chi Y , Rezaeian N Hassan , Hannan R , Jia X 
Published: July 2016

Purpose:Intra‐fractional prostate motion leads uncertainty on delivered dose in radiotherapy and may cause significant dose deviation from the planned dose distribution. This is especially a concern in scenarios with a high dose per fraction and hence a long delivery time, e.g. stereotactic body radiotherapy. Knowledge about intra‐fractional prostate motion is valuable to address this problem, e.g. by reconstructing delivered dose and performing adaptation. This study proposes a new approach to determine intra‐fractional prostate motion in VMAT via 2D/3D maker registration.Methods:At our institution, each patient has three markers implanted in the prostate. During treatment delivery, kV triggered images were taken every three seconds to acquire 2D projection of 3D anatomy at the direction orthogonal to the therapeutic beam. Projected marker locations were identified on each projection image using template matching with geometric constraints. 3D prostate translation and rotation for each triggered image were obtained by solving an optimization problem, such that the calculated marker locations match the measured ones. Inter‐image motion smoothness was employed as a constraint. We tested this method in simulation studies with five realistic prostate motion trajectories acquired via Calypso and in real phantom experiments.Results:For the simulation case, the motion range for these patients was 0.5∼6.0 mm. Root mean square (RMS) error of calculated motion along left‐right (LR), anterior‐posterior (AP) and cranial‐caudal (CC) directions were 0.26mm, 0.36mm, and 0.016mm, respectively. The motion range in the phantom study along LR, AP, and CC directions were 15mm, 20mm and 10mm. The mean RMS errors along these directions were 1.99mm, 1.37mm and 0.22mm.Conclusion:A new prostate motion tracking algorithm based on kV triggered images has been developed and validated. Clinically acceptable accuracy has been achieved.